Piton de la Fournaise

Photo of this volcano
Google Earth icon
  Google Earth Placemark
  • Country
  • Volcanic Region
  • Primary Volcano Type
  • Last Known Eruption
  • 21.244°S
  • 55.708°E

  • 2632 m
    8633 ft

  • 233020
  • Latitude
  • Longitude

  • Summit
    Elevation

  • Volcano
    Number

18 June-24 June 2014

OVPDLF reported that an eruption began at Piton de la Fournaise at 0120 on 21 June 2014 following a period of elevated seismicity. This new activity marks the end of more than three years of quiescence.

During 7-20 June volcano-tectonic and rockfall-type earthquakes were recorded, with the largest number occurring on 17 June. The locations of these earthquakes were relatively consistent between 500 and 1,200 m a.s.l. within Dolomieu crater. There were neither significant gas emissions nor indicators of pre-eruptive deformation. On 19 June, a field campaign by the Observatory team confirmed the activity detected by the permanent monitoring network (geodetic, thermal, and gas).

At 0006 on 21 June the seismic crises escalated and continued for 74 minutes. Localized deformation began at 0020 and continued for ~3 hours. Tremor began at 0120 and incandescence was observed by the remote cameras at 0135. The eruption was entirely contained within the Enclos Fouqué area on the ESE side of the central cone. Aerial observations by helicopter revealed an active lava fountain from a fissure that was within view of the Piton Bert webcamera. The fountaining built a spatter rampart and two lava flows extended ~1.5 km from the fissure. One lava flow extended 250 m after passing the Langlois crater (~2 km SE of Dolomieu crater); the second lava flow passed that crater on the E and S edge and extended an additional 500 m.

Public access to the volcano was restricted on 21 June and Alert Level 1 (“probable or imminent eruption”) was announced.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)

Index of Weekly Reports


2014: June
2010: January | September | October | December
2009: January | October | November | December
2008: August | September | October | November | December
2007: January | February | March | April | May
2006: August | October | December
2005: February | October | November | December
2004: January | April | May | August | September
2003: May | June | August | October | December
2002: January | November | December
2001: March | April | June | July | October | November
2000: November

Weekly Reports


18 June-24 June 2014

OVPDLF reported that an eruption began at Piton de la Fournaise at 0120 on 21 June 2014 following a period of elevated seismicity. This new activity marks the end of more than three years of quiescence.

During 7-20 June volcano-tectonic and rockfall-type earthquakes were recorded, with the largest number occurring on 17 June. The locations of these earthquakes were relatively consistent between 500 and 1,200 m a.s.l. within Dolomieu crater. There were neither significant gas emissions nor indicators of pre-eruptive deformation. On 19 June, a field campaign by the Observatory team confirmed the activity detected by the permanent monitoring network (geodetic, thermal, and gas).

At 0006 on 21 June the seismic crises escalated and continued for 74 minutes. Localized deformation began at 0020 and continued for ~3 hours. Tremor began at 0120 and incandescence was observed by the remote cameras at 0135. The eruption was entirely contained within the Enclos Fouqué area on the ESE side of the central cone. Aerial observations by helicopter revealed an active lava fountain from a fissure that was within view of the Piton Bert webcamera. The fountaining built a spatter rampart and two lava flows extended ~1.5 km from the fissure. One lava flow extended 250 m after passing the Langlois crater (~2 km SE of Dolomieu crater); the second lava flow passed that crater on the E and S edge and extended an additional 500 m.

Public access to the volcano was restricted on 21 June and Alert Level 1 (“probable or imminent eruption”) was announced.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


8 December-14 December 2010

On 9 December, OVPDLF reported that a seismic crisis at Piton de la Fournaise was followed by inflation of the entire summit region. Many small landslides occurred in Dolomieu crater. Later that day lava flows from two fissures on the N flank of Piton de la Fournaise, about 1 km NW of Dolomieu crater rim, traveled about 1.5 km N and NW. The next day seismicity and deformation measurements indicated that eruption of lava had stopped.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


27 October-2 November 2010

OVPDLF reported that an eruption from Piton de la Fournaise that began on 14 October from a fissure near the Château Fort crater, about 1.5 km SE of the Dolomieu crater rim, continued during 27-30 October. On 27 October steam plumes rose from the main vent (Cone 3) and lava flows were active. A sudden increase in tremor intensity was detected. The next day material was ejected from Cone 3, along with gas and steam. A small lava lake was observed in the cone, and lava flows continued to be active on the field. Tremor slightly decreased, and then significantly decreased on 29-30 October. No further tremor was recorded on 31 October and OVPDLF stated that the eruption had stopped.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


20 October-26 October 2010

OVPDLF reported that an eruption from Piton de la Fournaise that began on 14 October from a fissure near the Château Fort crater, about 1.5 km SE of the Dolomieu crater rim, continued during 19-25 October. On 19 October, explosive and degassing activity from vents along the fissure increased, but was still below the intensity noted at the beginning of the eruption. During 20-21 October small lava fountains fed lava flows that traveled as far as 2 km E and SE. Decreased gas emissions were concentrated to the S and W of the fissure. During 22-24 October fountains and gas emissions originated from one vent, and lava traveled ESE. Gas emissions decreased significantly.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


13 October-19 October 2010

OVPDLF reported that an eruption from Piton de la Fournaise began on 14 October near the Château Fort crater, about 1.5 km SE of the Dolomieu crater rim, after a seismic crisis was detected a few hours before. Lava fountaining occurred from four vents along a fissure. The Alert level was raised to 2 ("eruption in progress in the Fouqué caldera"). By 16 October, lava had traveled 1.6 km ESE, and was confined inside the Fouqué caldera. Lava fountains were 10 m high during 16-17 October and rose from two vents. On 17 October only one vent fed the lava flow. Scientists noted a reduction in tremor, a decrease in the rate of the lava flow, and less intense explosive activity and degassing. On 18 October lava was again ejected from two vents. The next day a hornito formed in the second vent and lava was ejected 5-15 m above a third vent.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


6 October-12 October 2010

On 11 October, OVPDLF reported a steady increase in the number and magnitude of volcano-tectonic earthquakes from Piton de la Fournaise since 7 October. During 10-11 October the summit area inflated 3-7 cm and an increase in the number of landslides in the crater was detected. The Alert level remained at 1 ("probable or imminent eruption").

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


29 September-5 October 2010

OVPDLF reported that on 29 September seismicity from Piton de la Fournaise remained high. Earthquakes were located at the base of the volcano, and inflation was noted particularly in the E. A significant number of landslides were detected in the crater. The Alert level remained at 1 ("probable or imminent eruption").

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


22 September-28 September 2010

Starting on 14 August and continuing through 10 September, OVPDLF recorded a slow but steady increase in the number and magnitude of earthquakes from Piton de la Fournaise. Inflation of the summit area began in late August. A report on 13 September noted localized deformation W of Dolomieu crater and a small number of landslides in the crater. On 20 September a significant increase in earthquakes was recorded, although the average magnitude was low. The earthquakes were located at the base of Piton de la Fournaise, W and S of Dolomieu crater. A seismic crisis on 24 September was characterized by several tens of earthquakes located beneath Dolomieu crater, and occurred in conjunction with 3 cm of inflation. The Alert level was raised to 1 ("Probable or Imminent Eruption").

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


6 January-12 January 2010

OVPDLF reported that during 5-7 January Piton de la Fournaise continued to erupt from a vent along a fissure high up on the SW Dolomieu crater wall. The vent produced lava fountains and flows that pooled in the bottom of the crater. On 7 January the vent closed, but the previously erupted lava continued to flow for the next few days. On 12 January, seismicity decreased and only minor gas emissions persisted.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


30 December-5 January 2010

OVPDLF reported that a seismic crisis at Piton de la Fournaise on 29 December was characterized by numerous earthquakes in the area W and NW of Dolomieu crater (max M 3), at depths of 1.1-2.2 km below the summit. Deformation was also detected. On 31 December, OVPDLF reported decreased seismicity and fewer landslides within Dolomieu crater on 30 and 31 December. On 2 January, an eruption from a fissure near the top of the W crater rim, preceded by a seismic crisis, produced lava fountains a few tens of meters high and lava flows in Dolomieu crater. Large landslides in Bory crater (W) along with the fissure eruption generated ash and gas plumes that rose above Piton de la Fournaise. During 2-3 January, seismicity and the number of landslides decreased. As of 4 January, the lava flows covered about 80 percent of the crater floor. Lava fountaining was still visible.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


9 December-15 December 2009

OVPDLF reported that on 14 December an eruption from Piton de la Fournaise was preceded by a seismic crisis and summit deformation. Sub-parallel fissures along the rim of Dolomieu crater fed lava flows on the S slope. A third fissure that also produced lava flows opened on the E flank. The lava stopped flowing during the night, after a gradual decrease. On 15 December, gas was emitted from the S and SE fractures and low-intensity tremor was detected.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


4 November-10 November 2009

OVPDLF reported that on 5 November a vent inside the S part of Piton de la Fournaise's Dolomieu crater opened, following an intense seismic crisis. Within thirty minutes, a fissure on the upper SE flank propagated E and a second fissure opened on the E flank. Lava fountains 20 m high and 'a'a lava flows were emitted from both fissures. The Alert Level was raised to 2. Lava flows ceased by the morning of 6 November; the Alert level was lowered to 1 later that day.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


14 October-20 October 2009

On 14 October, OVPDLF reported a seismic crisis from Piton de la Fournaise, with seismicity indicating deformation on the N side of Dolomieu crater and rockfalls within the crater. During 15-17 October, deformation and rockfalls continued to be detected. On 18 October, another seismic crisis was noted along with deformation on the N and S sides of Dolomieu crater. Aerial observations on 19 October revealed a small new fumarole in the crater. Changes in the chemical composition of the gases were also noted. A greater number and duration of rockfalls than in previous days was detected on 20 October.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


7 October-13 October 2009

During 5-6 October, OVPDLF reported increased seismicity from Piton de la Fournaise. A seismic crisis on 7 October prompted OVPDLF to raise the Alert Level to 1. Earthquakes were centered between the Bory and Dolomieu craters, and deformation was detected on the N side of Dolomieu. Seismicity remained above background levels during 8-13 October.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


21 January-27 January 2009

OVPDLF reported that the eruption from Piton de la Fournaise that began on 14 December 2008 was continuing on 27 January. Two vents were active; lava flowed to the bottom of Dolomieu crater through lava tubes and caused the crust from the pooled area to rise. Some incandescence was noted at night and at dawn.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


24 December-30 December 2008

OVPDLF reported that during 22-28 December lava from Piton de la Fournaise continued to issue from an active vent in the N part of Dolomieu crater, beneath "La Soufrière" and about 200 m below the crater rim. Gas plumes often reduced visibility. On 24 December, a small cone formed at the vent and occasionally produced lava fountains. During 27-28 December ten active channels were visible on the inner flanks of the crater. On 29 December, no lava was visible at the cone and lava flows were not apparent. The crater was sometimes filled with bluish gas during 29-30 December.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


17 December-23 December 2008

OVPDLF reported that during 16-23 December lava from Piton de la Fournaise continued to issue from two fissures inside Dolomieu crater and pond at the bottom of the crater.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


10 December-16 December 2008

OVPDLF reported that a seismic crisis at Piton de la Fournaise on 14 December was characterized by hundreds of earthquakes, many greater than M 2.5. On 15 December, an eruption began from two fissures inside Dolomieu crater and produced low-velocity lava flows that ponded at the bottom, covering about 20 percent of the 21 September lava flow.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


26 November-2 December 2008

OVPDLF reported that on 28 November after a period of increased seismicity Piton de la Fournaise erupted from the same vent that produced lava flows on 21 September. Lava flows issued from a fissure about halfway up the W wall of Dolomieu crater and ponded at the bottom, covering about 50 percent of the 21 September lava flow. A small quantity of Pele's hair was deposited inside Bory crater.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


29 October-4 November 2008

OVPDLF reported that a seismic crisis at Piton de la Fournaise on 31 October was characterized by hundreds of earthquakes. The Alert Level was not changed.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


15 October-21 October 2008

OVPDLF reported that a seismic crisis at Piton de la Fournaise on 20 October was located beneath the summit at an elevation of 700 m a.s.l. The crisis was accompanied by weak deformation.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


1 October-7 October 2008

OVPDLF reported that the eruption from Piton de la Fournaise that started on 21 September from the inner W wall of Dolomieu crater ended on 2 October. The total volume of erupted lava was about 850,000 cubic meters based on analysis of aerial photographs.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


24 September-30 September 2008

OVPDLF reported that during 24-30 September, lava flows from Piton de la Fournaise continued to pond at the bottom of Dolomieu crater. The lava flows issued from a fissure about halfway up the W wall of the crater. Based on air photos acquired on 25 September, the lava flow was an estimated 180 m long by 100 m wide and about 30 m deep. The erupted volume was about 300,000 cubic meters. On 26 September, lava fountaining from the fissure was no longer visible, but bubbling lava in the cone was noted.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


17 September-23 September 2008

OVPDLF reported an eruption from Piton de la Fournaise on 21 September. Lava flows issued from a fissure about halfway up the W wall of Dolomieu crater and ponded at the bottom. A strong concentration of sulfur dioxide was detected near the edge of the crater. On 22 September, Pele's hair was found scattered around the summit area and the lava flow rate decreased. This marked the first eruptive activity in the Dolomieu crater since the major collapse in April 2007 that enlarged the crater to 800 by 1,100 m wide and 340 m deep.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


10 September-16 September 2008

OVPDLF reported that small episodes of tremor from Piton de la Fournaise were recorded on 12 September. Field observations confirmed an increase in degassing from the SW part of Dolomieu crater and the presence of hydrogen sulfide. A seismic crisis was detected during 15-16 September. Numerous landslides followed the crisis, but may have also been associated with heavy rains. The Alert Level was not changed.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


3 September-9 September 2008

OVPDLF reported that a seismic crisis at Piton de la Fournaise during 8-9 September was characterized by hundreds of earthquakes. The Alert Level was not changed.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


27 August-2 September 2008

OVPDLF reported an increase of seismic activity beneath the summit of Piton de la Fournaise on 31 August. Deformation was also detected at the top of Dolomieu and, coupled with the increase in seismicity, prompted OVPDLF to raise the Alert level to 1. Public access to the summit was prohibited. On 2 September, the Alert Level was lowered because seismicity had decreased.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


13 August-19 August 2008

A small seismic crisis beneath the summit of Piton de la Fournaise lasted a little more than two and a half hours on 15 August. Deformation was also detected at the top of Dolomieu and, coupled with the increase in seismicity, prompted OVPDLF to raise the Alert level to 1. Public access to the summit was prohibited. On 18 August, the Alert Level was lowered because seismicity had decreased and deformation was no longer detected.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


6 August-12 August 2008

OVPDLF reported that a small seismic crisis beneath the summit of Piton de la Fournaise lasted about 10 minutes on 4 August. The strongest earthquake was a M 1.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


2 May-8 May 2007

OVPDLF reported that the eruption of Piton de la Fournaise ceased on 1 May. During 2-7 May, seismicity continued at and below the summit, and also indicated a large number of landslides from Dolomieu crater walls.

On 3 May, OVPDLF reported that in total, lava flows up to 30-40 m thick covered an estimated four square kilometers. The total estimated erupted volume was 120 million cubic meters, making this event one of the largest known historical eruptions of Piton de la Fournaise. Recent more accurate measurements indicated that Dolomieu crater collapsed to a depth of 350-360 m.

Sources: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF); Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


25 April-1 May 2007

OVPDLF reported that the eruption of Piton de la Fournaise continued during 25-30 April. Lava flows on the Brûlé set fire to vegetation on 25 April. Tremor remained very low in intensity.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


18 April-24 April 2007

OVPDLF reported that the eruption of Piton de la Fournaise from the S-part of the Grand Brûlé continued during 18-24 April. Tremor in this area remained very low throughout the reporting period. On 22 April, a large plume was visible from where lava flows met the sea. On 23 April, abundant lava flows in Grand Brûlé traveled in lava tubes. A collapsed lava-tube ceiling resulted in the formation of a hornito.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


11 April-17 April 2007

OVPDLF reported that the eruption of Piton de la Fournaise from the S-part of Grand Brûlé continued during 11-17 April. On 12 and 13 April, strong seismicity was followed by emissions; a gray plume from the summit of Dolomieu crater drifted NW. Also on 13 April, lava fountaining increased and resulted in several broad lava flows moving towards the sea. On 14 April, projected material reached 100-200 m above the point of emission.

Sources: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF); Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


4 April-10 April 2007

OVPDLF reported that on 30 March at 2300, a 9-hour eruption from the SE flank of Piton de la Fournaise produced a small lava flow. On 2 April, a fissure that opened on the S-part of Grand Brûlé also produced a lava flow that reached the sea later that day. The flow velocity was estimated at 100 cubic meters per second, a value not seen at Réunion Island within the last 20 or 30 years. Lava fountaining to 100 m was observed at the point of emission during 4-6 April. On 6 April, very liquid and fast-moving lava reached a higher velocity than on 2 April in the main channel and a'a' flows covered a broad area. Explosions and fragmentation of rock were observed at the point were the lava flows met the sea. Fine-grained particles and Pele's Hair were observed 10-20 km away and millimeter-sized grains of basalt were found within 5 km. Intense seismic activity was observed beneath the summit.

Based on aerial photographs on 7 April, an area of 1000 x 700 m of Dolomieu crater collapsed to an estimated depth of 300 m on the N side and 10 m on the NW edge; the estimated collapse volume was 50 million cubic meters. On 7 and 8 April, seismicity and the intensity of lava fountaining decreased. On 10 April, tremor decreased in frequency and two lava flows were observed, one reaching the sea.

Sources: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF); Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


28 March-3 April 2007

OVPDLF reported that on 2 April lava fountains about 50 m high erupted from a fissure at Piton de la Fournaise. The NW-SE-trending fissure was located SW of Dolomieu crater and was about 1 km long.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


14 February-20 February 2007

OVPDLF reported that on 18 February a small "seismic crisis" at Piton de la Fournaise began at 1611 and lasted only a few minutes. About 20 minutes later, based on seismic interpretation, an eruption at the summit began and ended the next day at 0155. A crack across Dolomieu crater was seen during an aerial observation on 18 February.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


3 January-9 January 2007

OVPDLF reported that the eruption of Piton de la Fournaise that began on 30 August 2006 ceased on 1 January

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


13 December-19 December 2006

OVPDLF reported that the eruption of Piton de la Fournaise that began on 30 August continued during 13-19 December. Lava flows covered the entire Dolomieu crater floor to a thickness of 10-30 m and spilled over the E rim of the crater, producing flows 100-200 m in length. A lava tube formed from a 27 November overflow of the Dolomieu crater drained lava on the E flank that traveled 2.5 km, S of crater Jean.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


11 October-17 October 2006

The eruption of Piton de la Fournaise that began on 30 August continued within the Dolomieu Crater. A new cone about 20-25 m high was formed in the SE part of Dolomieu and lava flows up to 10 m thick filled up 75% of the crater floor. The E part of the crater was filled up to the rim where lava flowed over and down the flank for hundreds of meters. On 9 October, a new crater formed about 100 m SW of the first one.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


30 August-5 September 2006

A small "seismic crisis" at Piton de la Fournaise began at 1000 on 30 August. A summit eruption started from the SSE edge of Dolomieu Crater at 1135 and scientists witnessed the opening of a fissure on the crater floor. A large portion of the crater floor was covered with lava by the afternoon. A second fissure opened just outside of the crater and produced a lava flow on the E flank. On 31 August, seismicity remained high and a new cone had formed in Dolomieu Crater.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


21 December-27 December 2005

Following summit inflation that had been measured at Piton de la Fournaise since the last eruption on 29 November, a seismic crisis began beneath Dolomieu Crater on 26 December at 1444. During the next 2 hours, seismicity shifted to the NE in the direction of "Nez Coupe de Sainte Rose." A first fissure opened at 1715 at the NE base of Piton de la Fournaise. At 2200 eruptive fissures opened in the caldera wall ~500 m E of "Nez Coupe de Sainte Rose," and a lava flow traveled into the "Plaine des Osmondes." By the 28th, eruptive activity was almost constant and an aa lava flow slowly traveled in the "Grandes Brule" and had reached to within ~3 km of the national road.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


23 November-29 November 2005

OVPDLF reported that immediately after the end of the last eruption at the Dolomieu crater of Piton de la Fournaise that began on 5 October 2005, the permanent Global Positioning System (GPS) network and extensometer network at the volcano continued to show strong surface deformation, which was a precursor for a new eruptive event. On 29 November at 0559 a seismic crisis began at the volcano and at 0625 tremor indicated the beginning of an eruption. A vent opened in the western part of Dolomieu crater and another vent opened on the volcano's N flank. Very little projected volcanic material was visible. A rapid and large lava flow traveled down the N flank in the direction of Piton Kapor. Inclement weather prohibited further observations. The Toulouse VAAC reported that ash from the eruption was not visible on satellite imagery.

Sources: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF); Toulouse Volcanic Ash Advisory Centre (VAAC)


5 October-11 October 2005

OVPDLF reported that an eruption started at Piton de la Fournaise on 4 October at 1426 after 4 months of almost continuous inflation and increased seismicity at the volcano. The eruption was preceded by a 56-minute-long seismic crisis and strong summit inflation. The low-intensity eruption occurred at Dolomieu crater and produced pahoehoe lava flows that covered a small area of the western part of the crater.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


23 February-1 March 2005

Contrary to reports that volcanic activity had ceased at Piton de la Fournaise on 19 February, the eruption continued through at least 25 February. After a period of low activity around the 19th, eruption tremor increased to high levels again on 21 February. Two eruption sites were active: the principal vent at 1,600-m elevation above the Plaine des Osmondes, and a vent at about 1,200-m elevation in the Plaine des Osmondes. The principal vent released a volcanic plume and several pahoehoe lava flows, but no lava fountains were visible. The second vent also released a very fluid pahoehoe lava flow. The lava flows covered a large area within the Plaine des Osmondes, and smaller lava flows traveled to about 600-m elevation in the Grand Brûlé.

On 24 February, shallow seismicity began beneath Dolomieu crater. It increased over time and by the 26th several hundreds of seismic events up to M 3 occurred. According to OVPDLF, these events may have indicated the possibility of a new pit crater forming within Dolomieu crater. On the 24th, visible signs of volcanic activity stopped within the Plaine des Osmondes, while eruption tremor slowly increased.

On the evening of 25 February, a lava flow from Plaine des Osmondes traveled down the Grandes Pentes, cutting the national road on its way to the sea. The lava flow covered a distance of ~5 km in about 2 hours. At the same time, seismicity on the North East rift zone above "Bois Blanc" appeared and a new vent opened within the "Trou de Sable" on the northern border of the "enclose" at 450-m elevation. This lava flow stopped about 100 m from the national road.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


16 February-22 February 2005

A new period of heightened seismic activity began at Piton de la Fournaise on 17 February around 1300, consisting of about 100 seismic events within 90 minutes. After that, the number of events decreased, but recommenced at 1638 with several hundreds of events. Strong deformation was recorded at the same time by tiltmeters and the extensometer network. Eruption tremor began around 2035, becoming strong at 2050. The eruption site seemed to be situated close to Nez Coupé de Sainte Rose (on the N side of the volcano), and lava flows were observed in the Grand Brûlé area. According to a news report, the eruption ended on 19 February.

Sources: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF); European Volcanological Society (SVE)


29 September-5 October 2004

The main recent eruption phase at Piton de la Fournaise began on 13 August 2004 and stopped on 2 September. It was followed by two minor phases from the main vent on the volcano's E flank; these, in turn, ceased on 3 October around 0300.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


1 September-7 September 2004

According to the Toulouse VAAC, a new eruptive episode began at Piton de la Fournaise on 4 September from a vent at sea level, near the town of St. Philippe on Réunion Island's SE side. Ash fell near the volcano's summit. A lava flow entering the sea produced a steam-and-ash plume that rose ~2.1 km a.s.l. Emissions ceased the morning of 7 September.

Source: Toulouse Volcanic Ash Advisory Centre (VAAC)


25 August-31 August 2004

According to the Société Volcanologique Européenne website, the eruption that began at Piton de la Founaise on 13 August continued through 31 August. The main lava flow entered the sea, building a large lava bench.

Source: Société Volcanologique Européenne


18 August-24 August 2004

Based on a news article, Société Volcanologique Européenne reported that the eruption that began at Piton de la Fournaise on 13 August continued through 20 August. Lava flowed N of Piton Madore.

Source: Société Volcanologique Européenne


11 August-17 August 2004

An eruption began at Piton de la Fournaise on 13 August after an increase in seismicity during 9-11 August. On the 13th, fissures that opened on the upper part of the Dolomieu crater emitted 2- to 3-km-long lava flows that traveled toward the sea.

Source: Société Volcanologique Européenne


4 August-10 August 2004

Seismicity and ground deformation that began to increase at Piton de la Fournaise in late June continued through 9 August. On the 9th, the seismic network recorded 50-70 low-intensity earthquakes. OVPDLF reported that this activity may be a precursor to an eruption in the next few days to weeks.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


19 May-25 May 2004

The eruptive episode that began at Piton de la Fournaise on 2 May stopped on 18 May. This followed 2 days of high eruptive activity when numerous pahoehoe lava flows and Pele's hair were produced. Around 1550 on the 18th the amount of eruption tremor decreased, completely stopping at 1615 and signaling the eruption's end.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


12 May-18 May 2004

The eruption that began at Piton de la Fournaise on 2 May continued through 15 May. After 2 days of low activity, eruption tremor increased by about a factor of 3 on the morning of 15 May. Lava flows followed the S border of Enclos Fouqué caldera and flowed down the Grandes Pentes area.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


28 April-4 May 2004

A new seismic event began at Piton de la Fournaise on 2 May at 1903, following one month of relatively high seismic activity at the volcano (with 10-30 earthquakes per day and two minor seismic crises) and continuous inflation at the summit. At 1936, eruption tremor began. The high intensity of tremor near Bory crater indicated that an eruption probably started within or very close to the crater. The Toulouse VAAC warned aircraft to be cautious in the airspace near the volcano.

Sources: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF); Toulouse Volcanic Ash Advisory Centre (VAAC)


7 January-13 January 2004

On 7 January at 0930 a seismic event started beneath Piton de la Fournaise and significant surface deformation was recorded. This event was different from past seismic events because it lasted for ~40 hours, while the hypocenters migrated to the NE. On 9 January eruption tremor started near Nez Coupé de Sainte Rose. A 300-m-long fissure, cutting the 1931 crater, produced a small ~2-km-long lava flow. The eruption stopped on 10 January around 1200.

Sources: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF); Agence France-Presse (AFP)


10 December-16 December 2003

As of 16 December, significant seismicity continued at Piton de la Fournaise. Hikers were only permitted limited access to the volcano due to the possibility of further volcanic activity.

Sources: Fournaise.info; Clicanoo - Le Journal de l'Ile de la Reunion


3 December-9 December 2003

Following around an hour of seismicity an eruption began on 7 December at 1535 in Piton de la Fournaise's Dolomieu crater. Lava fountaining to tens of meters was observed from two fractures on the SE crater floor. Two new fractures were also observed on the S crater rim that did not produce lava. The eruption decreased rapidly over the night of 7-8 December. By 8 December at ~1400 small incandescent lava flows and rock fall on the S crater wall were observed. By the night of 8 December the eruption ceased but strong degassing and fluctuating seismicity continued. New lava covered ~40% of the floor of Dolomieu crater. The eruption was preceded by a seismic swarm on 6 November that was followed by ~30 cm of steady uplift and 10-20 earthquakes recorded per day.

Sources: Fournaise.info; Clicanoo - Le Journal de l'Ile de la Reunion; Clicanoo - Le Journal de l'Ile de la Reunion


1 October-7 October 2003

A seismic swarm began at Piton de la Fournaise on 30 September at 2225 about 2 km beneath the SW area of Dolomieu crater. At 2330 eruption tremor began beneath the volcano's SSW flank. Then, a 400-m-long fissure opened at an elevation of ~2,350 m. Eruption tremor peaked on 1 October at 0100, began to decline at 0200, and ceased at 1300.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


27 August-2 September 2003

An eruption that began at Piton de la Fournaise on 22 August, stopped suddenly on 27 August at 2152. During the last 36 hours of activity, there was an increase in tremor intensity and lava emission. Afterwards, numerous long-period earthquakes were recorded.

Sources: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF); News.com.au - News Limited


20 August-26 August 2003

Following 5 months of slow inflation at Piton de la Fournaise and a series of eruptions during May to July, a new period of heightened seismicity began beneath Dolomieu crater on 23 August at 1848. The first fissure opened in Bory crater around 2120, and the second fissure opened at 2210 on the N flank at about 2,450 m altitude. Both fissures were active for short periods of time. The final fissure opened at 2330 around 2,200 m altitude on the N flank. A lava flow traveled into Plaine des Osmondes.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


25 June-1 July 2003

After ceasing for a few days, eruptive activity recommenced at Piton de la Fournaise on 21 June around 2330. Tremor was sometimes recorded at Dolomieu crater and lava flows were emitted from the crater. Volcanism continued through at least 28 June.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


11 June-17 June 2003

The second phase of an eruption that began on 30 May in the Dolomieu crater of Piton de la Fournaise ended on 6 June. Numerous seismic events were recorded during the following days until the morning of 12 June. On 13 June at 0308 eruption tremor again began within Dolomieu crater, marking the beginning of the third phase of the eruption. Eruptive activity resumed in the same area as the previous two phases. By 15 June no tremor was recorded, possibly marking the end of the third phase.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


4 June-10 June 2003

Tremor resumed at Piton de la Fournaise on 2 June, one day after the 30 May eruption ceased. An eruption began midday on 4 June, with lava emitted from the same place as the 30 May eruption and lava fountains rising ~15 m above the ground surface. By 5 June lava had traveled N inside Dolomieu crater, then E reaching ~500 m in length and 300 m in width. Tremor ceased on 8 June, marking the end of the eruption.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


28 May-3 June 2003

An eruption began at Piton de la Fournaise on 30 May around 1155 at Dolomieu crater in the area where the December 2002 collapse occurred. The eruption was preceded by a slight increase in seismicity on 28 May, which included a small seismic swarm. Another swarm took place on the morning of 30 May, and at 1155 tremor began beneath Dolomieu crater. Then the eruption began, producing a lava flow that reached a length of ~400 m and a width of 250 m in the western part of Dolomieu crater. In addition, lava fountaining was observed until ~1400, after which most surface activity ceased. By 1 June at 1000 no tremor was recorded, marking the end of the eruption.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


18 December-24 December 2002

OVPDLF reported on 19 December that after effusive activity stopped on 3 December very strong seismicity was recorded with more than 1,000 earthquakes occurring per day. The earthquakes were located a few hundred meters below Dolomieu crater. OVPDLF stated that crater collapse is possible.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


4 December-10 December 2002

Lava emissions from Piton de la Fournaise that had begun on 16 November ended on 3 December. Permanent tremor decreased significantly that day, although seismic events beneath the summit continued at a rate of one a minute. Sesimicity continued to decline over the next 2 days. Poor weather conditions prevented helicopter observations during 3-5 December. Inspection on 6 December revealed some areas of collapse between Bory and Dolomieu craters and white fumes that were released from a new cone named Guanyin. There was no evidence of surface activity coincident with larger seismic events that occurred while scientists from OVPDLF were on the edge of Dolomieu crater.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


27 November-3 December 2002

The eruption that began at Piton de la Fournaise on 16 November continued during 29 November to 3 December. On 29 November eruptive tremor increased by a factor of two, with 89 events recorded that day. On the 30th, 329 seismic events were recorded that were all located about 1 km a.s.l. beneath Dolomieu crater. A lava flow in the Grand Brûlé area approached the national road, crossing it around 2300. By about 0500 on 1 December the lava flow had reached the sea. At this time almost constant seismicity occurred at Piton de la Fournaise, with more than 1,500 earthquakes up to M 2.8 recorded. Eruption tremor was stable. Numerous long-period earthquakes were also recorded, indicating the presence of magma beneath the summit. On the morning of 2 December seismicity increased by about a factor of about three, and decreased the next day.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


20 November-26 November 2002

According to OVPDLF, the eruption that began at Piton de la Fournaise on 16 November continued through at least 26 November. During 20-26 November, visual observations were largely hampered by inclement weather. Eruptive tremor was constant on the 20th and 21st, and fluctuated on the 22nd. Tremor showed short-term variations during 23-26 November. Lava flows traveled in lava tubes between the active cone and 1,200 m elevation and traveled on the land surface at elevations between about 1,200 and 500 m.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


13 November-19 November 2002

After 3 months of high seismicity at Piton de la Fournaise and three small seismic crises, a strong seismic crisis with several hundreds of earthquakes started on 15 November at 2336. The earthquakes were accompanied by large deformation at the summit of up to 300 microradians. An eruption began on the 16th at 0433 with the appearance of eruption tremor on the volcano's E flank around 1,900 m-elevation. Fissures opened on the volcano's E flank between elevations of 1,900 and 1,600 m and lava flowed down the E flank. A small cone formed on one of the most active fissures around 1,600 m elevation.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


16 January-22 January 2002

After 12 days of activity the eruption that began at Piton de la Fournaise on 5 January ended on 16 January. The eruption's end was marked by a sudden, large decrease in lava emission at 1610 and the termination of eruption tremor at 1910. After the eruption ended a large number of long-period earthquakes were recorded below the summit and Plaine des Osmondes, indicating the continued presence of magma beneath the NE rift zone.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


9 January-15 January 2002

The eruption that began at Piton de la Fournaise on 5 January, continued through 15 January. There was a decrease in tremor during 7-11 January, with as few as 8 small earthquakes recorded per day at about 1-km depth. On 12 January tremor increased by a factor of two in comparison to the previous day and earthquakes were recorded about 4 km beneath the Plaine des Osmondes, near the N caldera wall. During the evening of 12 January, a new fissure opened at the base of the rampart in the lower part of the Plaine des Osmondes. Lava flowed from the fissure down into the Grand Brûlé close to the northern rampart. On 14 January lava flowed across the National Highway on its way to the ocean, entering it at 1540. By 15 January tremor was stable and about 100 earthquakes were recorded over a 24-hour period on the N side of the volcano. At 0600 a swarm of low-frequency earthquakes began near Bois-Blanc, a village on the island's E coast, NE of Plaine des Osmondes.

Sources: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF); Clicanoo - Le Journal de l'Ile de la Reunion


2 January-8 January 2002

Following several months of precursory activity an eruption began at Piton de la Fournaise on 5 January at 2300. Increased seismicity was recorded about a week before the start of the eruption; there were 17, 49, 62, and 70 earthquakes recorded on 26, 27, 29, and 30 December, respectively. The earthquakes were mainly located N of Dolomieu Crater at depths of 0.5-1.5 km with a maximum magnitude of 2.2. Inflation was recorded on 28 December and extensometers at Magnes and Châeau Fort recorded 0.28-mm-wide cracks on 31 December. The eruption that began on 5 January consisted of fire fountaining and lava flowing from four cracks that opened in the NE part of l'Enclos Fouqué caldera. By 6 January only two cracks remained active and lava flows reached ~1,100 m elevation. On 7 and 8 January tremor strongly decreased, but other seismicity persisted.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


7 November-13 November 2001

Increased seismicity and deformation at Piton de la Fournaise occurred for about 6 weeks prior to 12 November. On 5 November a seismic crisis occurred when 129 earthquakes were recorded that day. The earthquake's hypocenters were located 0.6-2 km under Bory crater. As of 12 November, approximately 30-50 earthquakes occurred per day, and slight swelling had been recorded at the summit.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


10 October-16 October 2001

Relatively high seismic activity originally detected in early September continued through 16 October, with about 16 earthquakes detected per day for approximately 3 weeks. The summit tiltmeter showed that slight inflation occurred, and extensometer stations at the N and S bases confirmed inflation by slight but constant fissure openings. Extensometer variations were about 3 to 4 times smaller than observed for previous eruptions. The volcano was at Alert Level 1.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


3 October-9 October 2001

OVPDLF reported that beginning in early September an increase in seismic activity was detected at Piton de la Fournaise, with ~10 seismic events per day. Beginning in early October seismic activity further increased with up to 20 events per day. Slight tilt variations detected S of Dolomieu Crater occurred simultaneously with the opening of fissures at two stations on the N and S flanks. The opening of the fissures indicated slight inflation at the summit. Piton de la Fournaise last erupted during June and July 2001.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


4 July-10 July 2001

The eruption that started on 11 June stopped on 7 July after 1 week of increased tremor. On 3 July tremor and the intensity of local earthquakes increased. The earthquakes had magnitudes less than 3 and were located under Dolomieu crater at a depth near sea level. On 6 and 7 July two aa lava flows in the Grand Brûlé area crossed the national highway. On 7 July the end of the eruption was marked by the disappearance of the tremor and a dramatic decrease in the intensity of local earthquakes.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


27 June-3 July 2001

Since 22 June constant tremor occurred that was associated with the eruption that began on 11 June. On 1 July an increase in tremor that occurred for about one hour was accompanied by strong degassing at a cone and a large amount lava emission. On 29 June new lava flows were observed in the Grand Brûlé area travelling to the N. By 2 July several dozen small flows were visible.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


20 June-26 June 2001

Tremor associated with the eruption that began on 11 June at Piton de la Fournaise continued under the volcano's E flank. Lava fountains were visible at two vents; at one vent strong degassing occurred, while at the other vent a boiling lava lake occasionally overflowed, sending lava flows towards the NE.

Sources: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF); Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


13 June-19 June 2001

Tremor associated with an eruption that began on 11 June had weakened by 16 June. The same day a fissure located on the E flank at the S base of crater Signal de l'Enclos at 1,800 m altitude was intensely active. In an area near the active fissure a cone began to form and lava fountains rose up to 30 m above the surface.

Sources: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF); Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


6 June-12 June 2001

Continuous extensometer and inclinometer variations have occurred since the beginning of April, and increased seismic activity has been recorded since the end of May. A short seismic crisis with 126 recorded events started at Piton de la Fournaise on 11 June 2001 at 1327. At 1350 extensometer variations indicated that a new eruption had started on the ESE flank, in the same area as the previous eruption on 27 March 2001. En echelon fissures started at about 2,500 elevation on the S flank, 200 m below the Dolomieu summit caldera. More fissures were located between 2,000 and 1,800 m elevation on the E flank at the southern base of crater Signal de l'Enclos and N of the Ducrot crater. Several lava flows descended the Grand Brûlé but their progression was very slow; at 1700 the front of the lava flow was still located at an elevation of 1,450 m. On the morning of 12 June, only the lower fissure at 1,800 m elevation was still active. It was ~200 m long, with several lava fountains 20-30 m high. The lava flow followed the northern border of the 27 March eruption and reached about 400 m elevation in the Grand Brûlé.

Sources: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF); Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


4 April-10 April 2001

The OVPDLF reported that the eruption that began at 1329 on 27 March ended on 4 April. During the eruption a ~ 2-km-long system of ESE-trending en-echelon fissures formed in an area 50 m below the S rim of the Dolomieu summit crater. The upper fissure was active for a few hours. The main eruption was focused on the ESE flank of the volcano, only 200 m N of the preceding October 2000 eruption. Aa flows approximately 5.5 and 2 km long traveled down the SE flank of the volcano. After one week of activity the eruption stopped following about 100 gas piston events at 0700 on 4 April.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


28 March-3 April 2001

The OVPDLF reported that after high seismic activity began at the end of January a final crisis started at Piton de la Fournaise at 1255 on 27 March. At 1320 an eruption began on the ESE flank of the volcano, with five "en-echelon" fissures. The final fissure is located at ~580 m in elevation and 200 m N of Morgabim crater, which was formed during the October 2000 eruption.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


21 March-27 March 2001

The OVPDLF reported that an eruption began in Dolomieu Crater at 1130 on 27 March. Additional details are not yet available, but inspection of photographs (http://www.ipreunion.com/) shows a fissure eruption, fountaining, and lava flows.

Sources: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF); Imaz Press Reunion


14 March-20 March 2001

The OVPDLF reported that instrumental measurements suggest that Piton de la Fournaise may be entering a phase of heightened activity. Periods of increased seismic activity were recorded in late January with up to 13 earthquakes per day, in late February to early March with up to 126 earthquakes per day, and from 10 March until at least 15 March with up to 20 earthquakes per day. Inflation was detected at the volcano's summit from mid-January to early February, and from the end of February to early March. Since mid-January a continuous opening of fissures was recorded at the N and S bases of the volcano, indicating inflation of the summit area. Similar variations in activity were observed before eruptions on the E and S flanks of the volcano in 1999 and 2000.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


15 November-21 November 2000

The OVPDLF reported that high amplitude tremor that occurred for about a week abruptly stopped at 1845 on 13 November, probably marking the end of the eruption. However, due to the recent seismic activity the volcano is being closely observed for signs of future eruptions.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


8 November-14 November 2000

According to OVPDLF, the eruption that began on 12 October at Piton de la Fournaise continued through 13 November. A new cone named "Piton Morgabim" developed in the beginning of November and on 8 November a 10- to 15-km-diameter lava lake formed, which had intense degassing and heavy lava fountaining. During the course of the eruption, 4.5-km-long lava flows formed E of the volcano in the "Grand Brûlé" area, and ~2-km-long lava flows issued from "Piton Morgabim."

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF)


Index of Monthly Reports

Reports are organized chronologically and indexed below by Month/Year (Publication Volume:Number), and include a one-line summary. Click on the index link or scroll down to read the reports.

10/1972 (CSLP 71-72) Four eruptive episodes since 18 June

11/1972 (CSLP 71-72) New vent with scoria cone observed 28 October

01/1973 (CSLP 71-72) Eruption observed from passing ship on 10 November 1972

11/1975 (SEAN 01:02) Eruption begins on 4 November after 31-month repose

11/1976 (SEAN 01:14) Lava flow during 2-3 November from fissure N of Dolomieu Crater

04/1977 (SEAN 02:04) Summary of first flank activity since 1800

05/1977 (SEAN 02:05) Lava extrusion ends, but one flow moved through a village

08/1977 (SEAN 02:08) Photographs of a lava flow and a damaged church

10/1977 (SEAN 02:10) New eruption emits lava flow towards uninhabited area

11/1977 (SEAN 02:11) Two fissures open in late October and emit lava flows

05/1979 (SEAN 04:05) Small lava eruption, lasting less than 1 day

07/1979 (SEAN 04:07) Small lava flows from two radial fissures

01/1981 (SEAN 06:01) Fissure eruption follows inflation and seismicity

02/1981 (SEAN 06:02) Voluminous lava effusion from new fissures

03/1981 (SEAN 06:03) Lava from new vents

04/1981 (SEAN 06:04) Lava flows, bombs, and ash from fissure vents

05/1981 (SEAN 06:05) Earthquake swarm; 1981 flows mapped

07/1983 (SEAN 08:07) 12-hour earthquake swarm

11/1983 (SEAN 08:11) Summit crater fissure eruption

12/1983 (SEAN 08:12) Lava emission continues; volcanic tremor

01/1984 (SEAN 09:01) Second phase of lava emission

02/1984 (SEAN 09:02) Tremor declines, then eruption ends

05/1985 (SEAN 10:05) Eruption with premonitory seismicity

06/1985 (SEAN 10:06) Fissure eruption follows seismicity and deformation

07/1985 (SEAN 10:07) Intrusion E of the summit; lava production resumes a month later

08/1985 (SEAN 10:08) Fissure activity resumes after 5-day hiatus

09/1985 (SEAN 10:09) Fissure eruption follows inflation and earthquake swarm

10/1985 (SEAN 10:10) Deflation after lava production ends

11/1985 (SEAN 10:11) Earthquake swarm then fissure eruption

12/1985 (SEAN 10:12) Inflation, earthquake swarm, then summit crater fissure eruption

01/1986 (SEAN 11:01) Summit lava production continues

02/1986 (SEAN 11:02) Eruptive episode ends

03/1986 (SEAN 11:03) First eruption outside caldera since 1977; evacuations; pit crater formed

04/1986 (SEAN 11:04) Collapse in summit zone

06/1986 (SEAN 11:06) Brief eruption from March pit crater

07/1986 (SEAN 11:07) Small pit crater eruption follows seismicity

11/1986 (SEAN 11:11) Ash eruption; lava from fissure

12/1986 (SEAN 11:12) Lava from fissure fills pit crater

05/1987 (SEAN 12:05) Seismicity, tilt, and summit intrusion

08/1987 (SEAN 12:08) Lava flows from summit crater

11/1987 (SEAN 12:11) New fissure eruptions

12/1987 (SEAN 12:12) Lava flows from fissures and tubes

01/1988 (SEAN 13:01) Strong seismicity then fissure eruption

02/1988 (SEAN 13:02) Lava production, tremor, and deformation

05/1988 (SEAN 13:05) Intrusion, then lava from fissure vents

07/1988 (SEAN 13:07) Minor lava production; deflation stops

09/1988 (SEAN 13:09) Deformation precedes fissure eruption

11/1988 (SEAN 13:11) New fissure eruption follows seismicity and deformation

12/1988 (SEAN 13:12) Fissure eruption in N part of caldera

01/1990 (BGVN 15:01) Nineteen hours of lava fountaining from central crater fissure after 3 months of seismicity

02/1990 (BGVN 15:02) Lava fountains and flows from summit-area fissure, with seismicity and deformation

04/1990 (BGVN 15:04) Lava production from summit caldera follows five days of increased seismicity

05/1990 (BGVN 15:05) Dike injection, then eruption from fissure vents near S caldera wall

07/1991 (BGVN 16:07) Brief lava production follows seismicity, deformation, and magnetic changes

09/1992 (BGVN 17:09) Summit fissure eruption follows 7 months of seismicity

12/1996 (BGVN 21:12) November intrusion signaled by radon and geophysical measurements

02/1998 (BGVN 23:02) First eruption in over 5 years begins 9 March

03/1998 (BGVN 23:03) Geophysical portrayal of the March fissure eruptions

06/1998 (BGVN 23:06) April-June lava flows on Plaines des Osmondes and beyond

07/1998 (BGVN 23:07) New lava flow traverses 12 km across the E flank

09/1998 (BGVN 23:09) Activity ends with fissure eruptions outside the caldera

07/1999 (BGVN 24:07) A fissure eruption begins 19 July

09/1999 (BGVN 24:09) September-October eruption generates lava fountains and flows

01/2000 (BGVN 25:01) A new eruption in February 2000 begins venting lava flows

07/2000 (BGVN 25:07) Eruptions in February, March, June, and July 2000

12/2000 (BGVN 25:12) 12 October-13 November eruption near July eruption site

05/2001 (BGVN 26:05) Eruptions during late March 2001 and on 11 June 2001

07/2001 (BGVN 26:07) 11 June-7 July eruption; two lava flows block highway

12/2001 (BGVN 26:12) Erupting fissures on 5-16 January 2002 in l'Enclos Fouqué caldera

11/2002 (BGVN 27:11) Fissure eruption 16 November-3 December sent lava to the sea

02/2003 (BGVN 28:02) Infrared data from November-December 2002 eruption

05/2003 (BGVN 28:05) Eruption on 30 May generates lava flows within Dolomieu crater

06/2003 (BGVN 28:06) Lava flows in Dolomieu crater; eruption ends 7 July

08/2003 (BGVN 28:08) Lava eruption from three fissures during 22-27 August

09/2003 (BGVN 28:09) Seismic crisis and a new SSW-flank fissure on 30 September

03/2004 (BGVN 29:03) December 2003 lavas spread across 40% of Dolomieu crater floor

05/2004 (BGVN 29:05) Elevated April seismicity followed by eruptive fissures and lava flows

12/2004 (BGVN 29:12) August-October eruption sends lava flows to the sea; pillow lavas

11/2005 (BGVN 30:11) Eruption on 5 October follows four months of heightened activity

06/2006 (BGVN 31:06) Eruption on 20 July 2006 after months of seismicity

01/2007 (BGVN 32:01) Extruding lava flows during 28 July-14 August 2006

12/2007 (BGVN 32:12) Caldera collapse in April 2007; large E-flank lava flows

02/2009 (BGVN 34:02) Quiet after April 2007 eruption; new eruption in September 2008

03/2010 (BGVN 35:03) Seismicity and eruptions January 2009 and November 2009-January 2010

03/2012 (BGVN 37:03) Increased seismicity and eruption during late 2010


Contents of Monthly Reports

All information contained in these reports is preliminary and subject to change.

All times are local (= UTC + 4 hours)

10/1972 (CSLP 71-72) Four eruptive episodes since 18 June

Card 1472 (25 October 1972) Four eruptive episodes since 18 June

The following information was received by letter on 24 October 1972.

"Piton de la Fournaise . . . has been erupting since 18 June 1972. The first observed activity was a slow aa flow of basalt, which was pouring from a fissure 0.5 m wide on the southern slope of the Fournaise. This activity lasted three days. No cinder nor spatter cones were built either at the upper end of the fracture or on the lava flows. This was due either to a possible gas-poor magma body or to a degassing located at the main crater (Cratère Brûlant = Scorching Center) of the Fournaise. But such a degassing was not actually observed.

"A first lull succeeded, which lasted for six weeks. The second phase started on 31 July and lasted two weeks. It was located at an altitude about 1,400 m above sea level, at a distance about 3 km NE from Cratère Brûlant. A cinder and spatter cone was built and lava flows ran on either side of the prehistoric cone Piton de Crac. They reached points about 3 km E from this Crac cone. (Three visitors lost their lives after 48 hours in the cold mists on the very rugged lava fields, locally named laves en gratons, or gratons.) The second lull lasted 3.5 weeks, from 13 August to 6 September. The third phase started on 6 September due N and 2 km away from Cratère Brûlant. It lasted for 4.5 weeks, until 8 October. A cinder cone was built and flows of basalt reached a length over 2.5 km.

"The third lull lasted less than one week and the present fourth phase started on 12 October at an altitude about 1,800 m above sea level SSE from Cratère Brûlant, about 2.5 km from its southern rim. On 17 October, when the CNRS-CEA (Commissariat à la Energie Atomique) team for volcanological research reached the place, a steep cinder cone some 20 m high had been erected. It contained a strongly fountaining lava pool, observed from helicopter, the level of which varies daily by several meters. In a three-day lapse of time, a welded rim of spatter 5-7 m high was built around the crater (on the top of the cinder cone). Lava flows are oozing from E and S foot of the cone and extend E over a surface about 1 km2.

"Four scientists (P. Lemercier and P. Raffini with the Abragam-Salvi differential magnetomer, and F. LeGuern and R. Cabot, with a modified Barnes radiometer, thermocouples, and gas-sampling and analysis outfit) are staying on the spot for about one week."

Information Contact: H. Tazieff, Directeur de Recherches au Centre Nationale de Recherches Scientifiques (CNRS), Paris, France.

11/1972 (CSLP 71-72) New vent with scoria cone observed 28 October

Card 1480 (06 November 1972) New vent with scoria cone observed 28 October

The following information was received by letter on 6 November. "Prof. Montaggioni, who flew over the volcano on 28 October 1972, reports that a new vent with subsequent scoria cone and eastwardly directed aa flow appeared at an altitude approximately 1,820 m above sea level on 26 or 27 October, 1 km due S from the fourth phase crater. The fourth phase vent was still active, with an important plume and red-hot lava lumps observable from the air."

Information Contact: H. Tazieff, Directeur de Recherches au Centre Nationale de Recherches Scientifiques (CNRS), Paris, France.

01/1973 (CSLP 71-72) Eruption observed from passing ship on 10 November 1972

Card 1535 (16 January 1973) Eruption observed from passing ship on 10 November 1972

The following report is from the logbook of the MV Flintshire, on a voyage from Penang to London. "10 November 1972 at 1800 GMT in 20°50'S, 57°22'E on course 244° at 21 knots. A reddish light was observed on the starboard bow. Examination of this, and later events, proved it to emanate from the southern end of Réunion Island at a distance of approximately 90 miles. At 30 miles distance, the red light resolved itself into what appeared to be a volcanic eruption, having two centers of activity a short distance apart, although at roughly similar heights (about 6,000-7,000 feet) and a hot lava flow from the western of the two centers. smoke could be seen rising but appeared to be drifting northwards. No violent activity was observed, the whole having the appearance of a gigantic bonfire. Visibility deteriorated after 2100 with the approach of a cold front." (Messrs. R. I.. Blackburne, Senior 2nd Officer and M. F. Tomlinson, 2nd Officer)

Information Contacts: Capt. M.G. Thomas, MV Flintshire; C.W.A. Browitt, Institute of Geological Sciences, Geophysical Laboratories, 6 South Oswald Road, Edinburgh 9, Scotland.

11/1975 (SEAN 01:02) Eruption begins on 4 November after 31-month repose

After a 31-month repose, the volcano began erupting on 4 November at the S end of Brulant Crater, 2,300 m above sea level. A 400-m-long fissure opened, trending NW-SE, and five cinder cones formed along its length. On 5 November one cone, 50 m high, was still active at the SE end of the fissure. A 10-m-wide lava lake formed. During the following 10 days 180,000 m3 of aphyric basalt aa was emitted. By 14 November the eruption was decreasing, the crater was degassing, and the lava flows were reported as small.

Further Reference. Krafft, M., and Gerente, A., 1977, L'Activite du Piton de la Fournaise entre Novembre 1975 et Avril 1976 (Ile de la Réunion, Ocean Indien): C.R. Acad. Sci. Paris, serie D, v. 284, p. 2091-2094.

Information Contact: L. Montaggioni, Univ. de la Réunion.

11/1976 (SEAN 01:14) Lava flow during 2-3 November from fissure N of Dolomieu Crater

An effusive eruption began at 1300 on 2 November from a 300-m-long fissure N of Dolomieu Crater. The eruption ended at 0400 the next day after producing a lava flow 1 km long. No casualties or damage were reported. Piton de la Fournaise had been dormant since the end of five months of activity on 6 April 1976 [Bulletin of Volcanic Eruptions (BVE), no. 16].

Information Contact: M. Krafft, Ensisheim.

04/1977 (SEAN 02:04) Summary of first flank activity since 1800

A new eruption of Piton de la Fournaise included its first flank activity since 1800. The following is a summary of events.

[24] March: Four fissures opened at 2,000 m altitude on the SE flank of the main crater (Dolomieu) and emitted lava for half a day.

4 April: Felt tremors began.

5 April: At 1700 a 500-m fissure opened at 1,900 m altitude in the NE quarter of the caldera (figure 1 and table 1) and extruded lava until the morning of 7 April.

Figure 1. Map of the fissures and lava flows at Piton de la Fournaise, 5-16 April 1977. The number beside each flow represents the date (in April) on which extrusion began. Vents 8, 9A, and 9B form a continuous fissure, and flows 8 and 9B overlap for most of their lengths. Courtesy of Maurice Krafft.

Table 1. April 1977 lava flows at Piton de la Fournaise and their durations of extrusion. Flow numbers are from figure 1. Dates are separated from start and stop times by colons.

    LAVA EXTRUSION DURING APRIL 1977
    Flow   Start              Stop

     5     05 April : 1700    07 April : 1200
     8     08 April : 1900    09 April : 1000
           12 April : 1400    12 April : 2400
     9A    09 April : 0700    09 April : 1200
     9B    09 April : 0930    10 April : 1000
           13 April : 0100    16 April : 1200
    11A    11 April : 1200    11 April : 1800
    11B    11 April : 1630    11 April : 2100

8 April: At 1900 an explosion was heard and a fissure opened at 1,300 m altitude on the N flank, producing lava fountains, gas, and a lava flow. The flow ceased 500 m from the village of Boisblanc during the night of 9 April.

9 April: A new fissure formed at 0700 near the 8 April fissure, extruding a lava flow that reached 700 m altitude. At 1100 another fissure opened (3 km N of the two previous ones) at 600 m altitude, from which a 50-m-wide flow moved during the night through the village of Sainte Rose, destroying 12 houses (figure 2). It widened to 250 m and reached the sea between 0230 and 0300 on 10 April.

Figure 2. Map of lava flows from Piton de la Fournaise through the village of Piton Ste. Rose, April 1977. Courtesy of Maurice Krafft.

11 April: A new fissure opened 500 m N of Sainte Rose but emitted only gas. During the afternoon, lava flowed towards the sea from the caldera (L'Enclos) [see 2:5].

12 April: Earlier flows stopped, but new activity, lasting from afternoon until about midnight, began at 1,500 m altitude above Boisblanc, near the 8-9 April eruption sites.

13 April: Lava again flowed from the NE quarter of the caldera during the morning [but see 2:5]. Lava extrusion resumed at 0100 from the fissure that had opened 9 April above Sainte Rose. The new flow reached the village at 1830, destroyed 21 houses and a church (figures 3 and 4), and entered the sea at 2200. About 1,000 people were evacuated, but no casualties were reported.

Figure 3. Oblique airphoto of Piton de la Fournaise looking SW. Flow 9B (of 9 April 1977) can be seen reaching the sea at right, and the caldera is at left. Photo by Maurice Krafft.
Figure 4. Destruction, by the lava flow at left from Piton de la Fournaise, of the church of Piton Ste. Rose, April 1977. Photo by Maurice Krafft.

Information Contacts: M. Krafft, Ensisheim; P. de Saint Ours, St. Maurice.

05/1977 (SEAN 02:05) Lava extrusion ends, but one flow moved through a village

The eruption ended about noon on 16 April with the cessation of lava extrusion from the fissure above Piton Sainte Rose (figure 1). Maurice Krafft reports that the lava described last month as flowing towards the sea on 11 April was a small flow (11 B on figure 1) originating from a fissure in the caldera wall (Rempart de Bois Blanc) and that the extrusion of a flow from the NE quarter of the caldera on 13 April is "very contested now."

Further References. Bout, P., 1979, Observations sur les Coulees de Basalte (Oceanites) des eruptions des 9-17 Avril 1977 de Piton Sainte-Rose (Réunion): 4ème Colloque de Geomorphologie Volcaniques: Problemes du Volcanisme Explosif: Clermont-Ferrand, Univ., Fac. Lett. Inst. Geogr., v. 57, p. 47-52.

Kieffer, G., Tricot, B., and Vincent, P.M., 1977, Une eruption inhabituelle (Avril 1977) du Piton de la Fournaise (Ile de la Réunion): Ses Enseignements Volcanologiques et Structuraux: C.R. Acad. Sci. Paris, serie D, v. 285, p. 957-960.

Information Contact: M. Krafft, Ensisheim.

08/1977 (SEAN 02:08) Photographs of a lava flow and a damaged church

[No report accompanied the photographs originally in this issue, so they have been placed in the preceeding report of the April 1977 activity.]

Information Contacts: M. Krafft, Ensisheim, France.

10/1977 (SEAN 02:10) New eruption emits lava flow towards uninhabited area

An eruption at Piton de la Fournaise began 24 October 1977. Lava flowed toward an uninhabited area at the reported initial velocity of 1 km/hour.

Information Contact: UPI.

11/1977 (SEAN 02:11) Two fissures open in late October and emit lava flows

Two fissures opened during the morning of 24 October on the E slope of Dolomieu Crater, within the caldera. The first fissure opened at 2,180 m altitude at 0830, and emitted an aa lava flow, which stopped the next day after traveling to 500 m altitude. The second fissure opened one hour after the first at 1,920 m altitude. Moderate explosive activity from this fissure built a single tephra cone until 26 October, when a second, immediately adjacent cone began to grow. Activity from the two cones remained fairly constant until lava fountaining began on 1 November. Fountains initially rose 200 m above the cones, but gradually declined until 10 November, when new lava covered 4 km2. Fountaining re-intensified 10-13 November, and was succeeded on 14 November by effusion of basaltic lava flows, with velocities reaching 60 km/hour. No casualties or damage occurred. The eruption ended at 1250 on 17 November.

Further Reference. Kieffer, G., and Vincent, P.M., 1978, The October-November 1977 Eruption of Piton de la Fournaise (Réunion Island): A terminal eruption without terminal crater: C.R. Acad. Sci. Paris, serie D, v. 286, p. 1767-1770.

Information Contact: M. Krafft, Cernay.

05/1979 (SEAN 04:05) Small lava eruption, lasting less than 1 day

A small eruption began during the evening of 28 May and ended about noon the next day. A 100-m-long fissure opened ~1.5 km SE of Cratère Dolomieu, extruding a lava flow 150 m in length (figure 5). Three spatter cones formed on the fissure.

Figure 5. Map of the caldera of Piton de la Fournaise from Krafft and Gerente (1977). The approximate site of the May 1979 activity is indicated by an X.

Information Contact: M. Krafft, Cernay.

Reference. Krafft, M., and Gerente, A., 1977, L'activité du Piton de la Fournaise entre Octobre 1972 et Mai 1973: C.R. Acad. Sci. Paris, Serie D, v. 284, p. 607-610.

07/1979 (SEAN 04:07) Small lava flows from two radial fissures

A small eruption began when two radial fissures opened almost simultaneously on the N and S flanks of Cratère Dolomieu (the central crater) at about 1845 on 13 July. A line of three small fountains, each 50 m high, formed along the N flank fissure and aa lava flowed 400 m downslope. N flank activity ended at about 2200. Ten spatter cones were generated by the 0.5-km-long S-flank fissure and a second aa flow traveled 1.5 km before the eruption stopped at 1130 on 14 July.

Information Contact: M. Krafft, Cernay.

01/1981 (SEAN 06:01) Fissure eruption follows inflation and seismicity

A summit area eruption began on 3 February after 12 days of local earthquakes and 17 cm of summit inflation. After a fairly sudden onset of seismicity 23 January, about forty M 2 events were recorded daily by the newly established Observatoire Volcanologique du Piton de la Fournaise. The day before the start of the eruption, 73 earthquakes were recorded, with foci ~1 km beneath Cratère Bory, the smaller of the two summit craters. Seismicity intensified in the hour prior to the first eruptive activity on 3 February. About 250 small discrete events were followed by 5 minutes of harmonic tremor. At 2030 a small fissure opened in Cratère Bory. A minor lava flow was extruded during 2 hours of activity along this fissure and a 6-m-high hornito formed at the vent. During the second hour of the eruption, a small amount of aa lava flowed from a vent 200 m below the rim separating the larger Cratère Dolomieu from Bory. This lava covered about 3/4 of a small crater ruin (Enclos Velain) between Bory and Dolomieu. After about 2 hours, two or three small fissures opened on the NE side of Cratère Dolomieu, each extruding a lava flow 100 m long.

The next morning at about 0400, a 300-m-long N-S-trending fissure formed lower on the NE side of Dolomieu. Three spatter vents were active initially, but within an hour fountaining (15-30 m high) was limited to the lower portion of the fissure. Lava flowed downslope through channels and tubes onto the caldera floor.

As of early 6 February, lava fountaining as much as 70 m high was continuing from a 30-m-long segment of the lower end of the fissure. The activity had built a small, elongated cone with three vents. The lava flow, composed of aphyric basalt, was 1.5-2 km in length and covered several thousand square meters of the caldera floor (figure 6). Seismicity beneath Cratère Bory had stopped a few hours after the eruption began, but small events were occurring 6 February beneath Nez Coupé de Ste. Rose, on the caldera's N rim.

Figure 6. Map showing the eruption fissures and lava flows from the three phases of the 3 February-5 May 1981 eruption of Piton de la Fournaise. Map prepared by F.X. Lalanne, Observatoire Volcanologique de la Réunion.

This eruption produced more lava than the two most recent eruptions, 28-29 May and 13-14 July 1979. However, the 1981 volume is of the same order of magnitude as has been extruded in most of its numerous lava flow eruptions from the summit area in the past 50 years.

Information Contacts: L. Stieltjes, BRGM, Réunion; Volcano Observatory of Réunion; M. Krafft, Cernay.

02/1981 (SEAN 06:02) Voluminous lava effusion from new fissures

Lava extrusion that began 3 February from the N side of the updomed summit region that surrounds Bory and Dolomieu craters continued until 25 February. After about 13 hours of seismicity, fissures opened on the SW side of the summit area and began to eject lava. The eruption was continuing as of 3 March.

Activity N of the summit, 3-25 February. During the first few days of the eruption, lava was extruded from a series of radial fissures in the N summit region. By 6 February, lava fountaining was confined to a spatter cone at 2350 m altitude at the lower end of a fissure that opened 4 February. Lava flows emerged from one or two vents 300 m down slope from the active spatter cone and moved 1.3 km to the E. Fountaining was most intense 10 February (30 m high) and 18 February (100 m high). About 19 February, a small lava lake formed inside the active cone. Lava fountains rose a few m above the lake surface. A 2-m-diameter vent high on the cone emitted blue and yellow flames 3-4 m high. The spatter cone partially collapsed 20 February. Lava overflowing the collapsed area formed a front 100 m wide.

Fountaining and extrusion of lava flows began a rapid decline on 23 February and stopped on the 25th. Several million cubic meters of lava were extruded 3-25 February.

Activity SW of the summit beginning 26 February. Seismographs at Réunion's volcano observatory began to record a series of small (about M 1) local earthquakes around midnight of the night of 25-26 February. Earthquakes became increasingly frequent that morning and by 1230 were occurring once every 15 seconds under the summit's Bory Crater. Harmonic tremor started at 1300 and the beginning of eruptive activity was observed at 1306. Two minutes later, a large, black cloud rose to 2 km height. Two en-echelon radial fissures, trending N74°E, opened on the SW side of the updomed summit region. The upper fissure, 200-300 m long, extended from 2,400 to 2,250 m altitude. The lower fissure, offset 100 m from the base of the upper fissure, extended 100 m farther downslope. Lava fountains rose to 15 m height from the entire length of the upper fissure, while fountains from the lower fissure were 50-60 m high. After half an hour, lava from the two fissures had merged into a single aa flow 2 km long that spread onto the caldera floor and moved toward the S caldera wall. Mid-afternoon outflow rates from the two fissures were ~300 m3/s (~1 x 106 m3/hour), much higher than at any time during the N summit region activity earlier in the month. The lava was an aphyric basalt, as was the 3-25 February material. By about 1800, lava fountaining along the upper fissure was concentrated at its lower end, where a cone was growing. Seismicity ended within a few hours of the start of eruptive activity on 26 February, a pattern similar to that observed at the beginning of the eruption 3 February.

Lava fountaining along the entire lower fissure continued until 0200 on 27 February, then was limited to the middle of this fissure, where a cone formed. The rate of lava outflow declined to 60 m3/s by the morning of the 27th and 10 m3/s the following day. Fountaining from the upper fissure stopped 28 February but continued from the lower fissure, building a 15 m-high spatter cone. Two other spatter cones formed along the lower fissure 1 March, with activity concentrating at one of these, also 15 m high, on 2 March. The rate of lava production remained at 10 m3/s as of 2 March [but see 6:4], feeding a slow-moving lava flow that was incandescent for the upper 1.5 km of its length.

Further References. Bachelery, P., Blum, P.A., Cheminée, J.L., et al., 1982, Eruption at le Piton de la Fournaise Volcano on 3 February 1981; Nature, v. 297, p. 395-397.

Blum, P., Gaulon, R., Lalanne, F., and Ruegg, J., 1981, Sur l'Evidence de precurseurs de l'eruption du Volcan Piton de la Fournaise a la Réunion (Fevrier 1981): C. R. Acad. Sci. Paris, v. 292, serie II, p. 1449-1455.

Information Contacts: M. Krafft, Cernay; L. Stieltjes, BRGM, Réunion; Volcano Observatory of Réunion.

03/1981 (SEAN 06:03) Lava from new vents

The activity SW of the summit that began 26 February continued until 25-26 March. A new eruption on 1 April was preceded by a swarm of local earthquakes, starting at 1923. The seismographs at Réunion's volcano observatory registered 72 discrete events in the next few hours, before the onset of harmonic tremor and the start of an eruption at 2141. Observatory personnel reported that lava extruded from a vent in the north-central area of the caldera, 3 km ENE of the summit, flowed toward the N caldera wall, reaching it during the night. By the early afternoon of 2 April, the flow front was 1 km W of the coast highway [but see 6:4], but the lava's rate of advance had slowed considerably.

Information Contacts: J. LeMouel and J-L. Cheminée, IPG, Paris.

04/1981 (SEAN 06:04) Lava flows, bombs, and ash from fissure vents

As lava extrusion N of the summit was ending, seismic activity resumed on 25 February. By 0400 on the 26th, 50 events had been recorded, 20 with magnitudes greater than 1. Seismographs registered an additional 521 local earthquakes, 111 of M 2 or greater, between 0400 and 1304. Harmonic tremor began as two en-echelon fissures, trending 215°, opened ~800 m SW of Cratère Bory at 1304. Aphyric basalt flows had reached 2 km in length by the next morning when lava was pouring from the fissures at a rate of 600 m3/s (2 x 106 m3/hour). By 1 March, the outflow rate had declined to about 20 x 106 m3/s and a 400-m-long segment of the flow was moving through a lava tube. Lava fountains reached an average height of 20-40 m. Blue and green flames were nearly always visible over the fissures. Three vents remained active 2 March, but by 4 March fountaining continued from only one vent, reaching an average height of ~20 m. By the 4th, lava had reached the break in slope above the caldera wall and most of the flow travelled through tubes. The flow reached the S caldera wall, at 1,900-2,000 m altitude, on 7 March.

Seismicity, which had remained quiet since 26 February, resumed on the morning of 7 March when 500 events were recorded, all with magnitudes <1.0. On 9 March, 700 more events, again with magnitudes <1.0, were recorded between 0819 and 1651 from a seismic station on the N side of the caldera. Between the 13th at 1000 and the 15th at 2344, the same station recorded 50 more events, 22 of which had magnitudes of 1 or more.

The lava flows spread laterally as the rate of outflow slackened 16-21 March. Lava reached 1800 m altitude and the flow front was ~5 km from the vents. The activity declined progressively, ending completely 25-26 March. A levelling network W of the summit was reoccupied 11 March, indicating that a net inflation of 11 microradians had occurred since the last survey on 13 February.

After about 2 hours of local seismicity, a 1-km-long fissure trending 060° opened on 1 April at 2141, between 1,900 and 1,600 m altitude about 2 km NE of the updomed summit crater area (figure 6). Olivine basalt lava flowed rapidly downslope 1 and 2 April, stopping at 480 m altitude ~2.3 km W of the coast highway. On 3 April, effusive activity was limited to two vents along the fissure at 1,650 and 1,600 m altitude. Intense explosive activity ejected lava fragments to an average height of 50 m, building two cones, while numerous flows (as many as a dozen at once, 200-300 m in length) moved as much as 1 km toward the N caldera wall. Activity at the upper vent stopped 6 April. Many phreatomagmatic explosions occurred 7 April, of which two were observed between 1200 and 1700. A large quantity of cauliflower bombs and ash were ejected.

Poor weather prevented observations for the next 13 days. By 22-24 April, when weather had cleared, tephra ejections were reaching an average altitude of only 30 m. Lava flowed from the ends of tubes, forming numerous small tongues of aa and pahoehoe tens of m in length. A 2 km by 300 m field of lava had formed by the 24th.

On 3 and 4 May the explosive activity ceased as effusive activity weakened. Only three aa flows persisted in the lava field, one 300 m long, the other two only 10 m in length. By the night of 4-5 May, all eruptive activity appeared to have ended.

Heavy rains stopped some of the seismometers from working, but the 1-2 instruments that remained functional recorded no seismicity after the premonitory swarm on 1 April. No significant changes in tilt were measured.

Information Contacts: J. LeMouel and J-L. Cheminée, IPG, Paris; M. Krafft, Cernay.

05/1981 (SEAN 06:05) Earthquake swarm; 1981 flows mapped

An earthquake swarm beneath the N caldera rim began suddenly on 18 May at 1000. By 2200, 800 small events had been recorded, but no eruption followed.

Information Contacts: J-L. Cheminée, IPG, Paris; M. Krafft, Cernay.

07/1983 (SEAN 08:07) 12-hour earthquake swarm

A 12-hour earthquake swarm occurred 15 July at Piton de la Fournaise, the first seismic crisis there since shortly after the 3 February-5 May 1981 eruption, which produced 10 x 106 m3 of lava during three active phases. Since then, background seismicity had been less than 0.5 events/day. The 21 events between 0830 and 2015 on 15 July occurred in the central area at shallow depth but were poorly located because they were recorded on only 1-3 stations, have emergent onsets, and poorly-defined phases. Event durations ranged from 15 to 150 seconds. The seismic crisis prompted the resurvey of deformation networks, but no significant changes were measured.

The Observatoire Volcanologique du Piton de la Fournaise noted that for the past 50 years the mean eruption frequency has been one every 12-14 months. The 27 months since the last eruption is one of the longer repose intervals during that period.

Information Contact: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF), Réunion.

11/1983 (SEAN 08:11) Summit crater fissure eruption

The following quoted reports are from the OVPDLF. "Eruptive activity started 4 December at 0900, preceded by an increase in seismicity that began 20 November [corrected from 2 November]. From 20 November, the seismic events clustered at depths of about 1.5-5 km beneath the summit area. The maximum number of earthquakes was recorded 1 and 2 December, with 10 events (M <1) per day. The strain release was not very large. A seismic swarm began 4 December at 0642. About 300 events were recorded by 0859, when harmonic tremor began, and a few minutes later the eruption was seen. The initial eruption fissure was situated on the SSW flank of the central cone (Cratère Dolomieu). Activity at two segments of this fissure stopped during the evening. A second fissure zone opened at 1027 and stopped erupting about 1400; a third fissure opened at 1319 and ceased erupting about 0700 the next morning. The amount of lava extruded 4 December was estimated at 1 x 106 m3. The initial fissure was the most productive. Only weak deformation was measured before and during the eruption."

Information Contacts: J. Lenat and F. Lalanne, OVPDLF; Univ. de la Réunion; J. LeMouel and J-L. Cheminée, IPG, Paris.

12/1983 (SEAN 08:12) Lava emission continues; volcanic tremor

"The eruption was continuing as of 5 January, but the effusive and explosive activity and tremor amplitude had decreased. A rough estimate of the total magma output through 5 January was 10 x 106 m3, about double the volume that had reached the surface by 14 December (figure 7).

Figure 7. Map showing the 1983 lava flows (shaded) and eruption fissures at Piton de la Fournaise as of 14 December. Older craters and fissures are dated and the 1972 lava flow is outlined with dots. Activity stopped on 4 December 1983 at about 1400 along fissure zone 2 and about 0700 the next day along fissure 3. Courtesy of OVPDLF.

"A resurvey of the deformation networks during the days following the onset of the eruption has shown that ground deformation has taken place in the summit area. Tilt and distance measurements indicate an inflation centered S of the summit craters with a shallow focus. Records from a continuously recording strainmeter in the summit area indicate that the major part of the ground deformation happened within 1/2-3/4 hour (figure 8). [Rapid deformation started about two hours before the eruption and just after the beginning of the seismic swarm associated with the intrusion toward the surface (figure 9)]. No other significant ground deformation has been observed during the course of the eruption through 21 December.

Figure8. Extension in mm, detected at Piton de la Fournaise on 4 December 1983 between midnight and 1400 by a continuously recording strainmeter in the summit area. Courtesy of OVPDLF.
Figure 9. Pre-eruption seismic cross-section through the summit of Piton de la Fournaise, with hypocenters and magnitudes between 20 November and the onset of the pre-eruption swarm of 4 December 1983. The three initial swarm events are also shown. Courtesy of OVPDLF.

"Since the beginning of the eruption, the only recorded seismic activity has been volcanic tremor with amplitude that varied with time."

Information Contacts: J. Lenat, A. Bonneville, P. Tarits, and H. Delorme, OVPDLF; P. Bachelery and J. Bougeres, Univ. de la Réunion.

01/1984 (SEAN 09:01) Second phase of lava emission

"A second eruptive phase began on 18 January at 0454, preceded by inflation of the summit area that began in early January. A seismic swarm of about 50 low-energy events occurred between 0313 and 0454 on 18 January when harmonic tremor began. The eruptive fissure of the first phase, which began on 4 December, was still active (but with virtually no explosive activity and a low level of effusive activity) when the second phase began, but apparently ceased during the day on 18 January.

"Two new eruptive fissures formed ~400 m NNW of the main first phase fissure. Activity at the upper one rapidly decreased, and stopped at 0200 on 19 January. The other, ~200 m long, sustained lava fountaining more than 80 m high 18-19 January. The fountains produced a large amount of Pele's hair that was transported SW by wind and deposited on inhabited areas, causing a potential hazard for livestock grazing in the area. Emergency measures were taken by local authorities; fortunately, heavy rains and wind 19-23 January washed away most of the tephra that remained on the grass.

"During 18 January, the lava discharge was vigorous (up to 100 m3/s). At 1200 the flow extended 4 km from the vents. Inflation, possibly related to the emplacement of an intrusion, was measured on 18 January, showing the same pattern as after the start of the first phase on 4 December.

"On 24 January, the eruption was localized at two vents that were building two cinder cones. On 27 January, only one of the vents was still active. Eruptive activity was continuing as of 8 February."

Information Contacts: J. Lenat, A. Bonneville, C. Hemond, F. Lalanne, and P. Tarits, OVPDLF, Réunion; P. Bachelery and J. Bougeres, Univ. de la Réunion.

02/1984 (SEAN 09:02) Tremor declines, then eruption ends

"The eruption ended 18 February. During the previous days tremor amplitude had become irregular with periodic bursts. In the last 12 hours of the eruption, the tremor was intermittent, with bursts occurring less and less frequently. The sporadic tremor progressively died away during the afternoon of 18 February and an observation from the rim of the previously active vent brought confirmation that lava was no longer present at the bottom of the crater although it was still red hot."

Further References. Bachelery, P., 1984, L'Eruption du Piton de la Fournaise (Réunion) 12-83/02-84: Bull du Lab de Geog Phys, Univ. de la Réunion, no. 1, sommaire, p. 2-14.

Lenat, J.F., Bachelery, P., Bonneville, A., Tarrilo, P., Cheminée, J.L., and Delorme, H., The December 4, 1983 to February 18, 1984 eruption of Piton de la Fournaise (La Réunion, Indian Ocean): Description and Interpretation: JVGR, in press.

Information Contact: J. Lenat, OVPDLF.

05/1985 (SEAN 10:05) Eruption with premonitory seismicity

"Since the last eruption, seismicity and deformation measured at the four summit stations had remained at very low levels (0-5 earthquakes and 1-7 µrad of tilt per month). The pattern of tilt vectors implied a progressive deflation of the area that had undergone large deformation during the last eruption.

"Beginning on 15 May, several small earthquakes (M <1) were recorded at depths of 1.5-2.5 km beneath the summit. Simultaneously, the summit dry tilt stations began to show an inflationary pattern. The number of seismic events progressively increased. Seismic activity peaked on 8 June with 13 events, and decreased to a low level on the 13th. No significant migration of the earthquakes was observed. Inflation appeared to have been almost continuous except during two episodes when deformation slowed (3 June) or reversed (8 June) corresponding to the periods of largest seismic energy release.

"This activity differed from the 1983 pre-eruptive crisis. The late 1983-early 1984 eruption was preceded by two weeks of seismic activity (48 events) with no associated deformation. The most recent activity lasted for at least four weeks. The earthquakes are located in the same area as before, but summit tilt stations show inflation of 15-40 µrads."

Information Contacts: J. Lenat, OVPDLF; M. Kasser, Inst. Geographique National (IGN), Paris; A. Nercessian, IPG, Paris; R. Vie le Sage, Délégation aux Risques Majeurs (DRM), Paris; P. Bachelery, Univ. de la Réunion; A. Bonneville, Univ. du Languedoc; G. Boudon, Obs. Volc. de la Mt. Pelée; M. Halbwaks, Univ. de Chambéry.

06/1985 (SEAN 10:06) Fissure eruption follows seismicity and deformation

"An eruption began on 14 June at 1604 on the SW flank of the central cone (figure 10), just as in the July 1979, February 1981, December 1983, and January 1984 eruptions. The main eruptive fissure, oriented 230°, was ~1 km long and composed of four main en-echelon fractures. A small fissure oriented 330° was located NW of the summit. The NW fissure and the upper part of the SW fissure were active for 2-6 hours after the beginning of the eruption. Activity stopped on the lower part of the SW fissure on 15 June at about 1600. Flows were emitted all along the fissure, the longest extending ~2 km from it. No calculation of emitted volume has yet been made, but a crude approximation is 1 x 106 m3.

Figure 10. Sketch map of the central and south parts of the Piton de la Fournaise caldera, showing lava flows from the 1983-84 and 1985 eruptions, and vents from earlier eruptions. Courtesy of OVPDLF.

"This eruption was preceded by a 30-day pre-eruptive seismic crisis and by a 40-minute intrusive seismic swarm. Seismicity had been at background levels since the end of the 1983-84 eruption. The pre-eruptive seismic crisis began on 15 May and the number of recorded earthquakes has increased since then (figure 11). All were located beneath the summit at a mean depth of 1.5-2.5 km. The duration of the pre-eruptive seismic crisis and the number of events have been greater than for the December 1983 eruption, but the location of events has been the same.

Figure 11. Chronology of the 1985 pre-eruption seismic crisis at Piton de la Fournaise. Each box represents one earthquake. Box heights represent earthquake durations. Courtesy of OVPDLF.

"Since the end of the 1983-84 eruption, the deformation has been small, which could be interpreted as a relaxation of the area that had undergone large displacements during the two intrusive crises related to the 4 December 1983 and 18 January 1984 outbreaks. A pattern of inflation of the central area has been measured since May 1985. This inflation developed during the pre-eruptive crisis and was in the range of 20-50 µrads at the dry-tilt stations located near the summit. Inflation was not seen at the stations more than 2-3 km from the summit.

"Figure 12 shows the chronology of seismicity 14-15 June and detailed plots of the 40-minute intrusive period. As the intrusion approached the surface, local surface movements occurred, as shown by strainmeters across an open fissure and by the tiltmeter ~200 m from the eruptive fissure.

Figure 12. Seismicity at Piton de la Fournaise, 14-15 June 1985. Top, relative amplitude of harmonic tremor at BOR station, ~200 m from the fissure, 14-15 June; center, cumulative duration of seismic activity (in seconds) during 5-minute intervals, 14 June between 1200 and 1700 hours; bottom, tiltmeter and strainmeter data at BOR station, 14 June, 1200-1700. Arrows at top and center mark the start of the eruption, as does the right-hand vertical dashed line in the tilt/strain section of the figure. Courtesy of OVPDLF.

"The lava of the 14-15 June eruption is a transitional aphyric basalt with a composition (table 2) similar to that of the 1983-84 basalt. This supports the hypothesis that the shallow magma chamber could not have been replenished before this eruption.

Table 2. Composition of two samples of the 14-15 June 1985 basalt from Piton de la Fournaise. Courtesy of OVPDLF.

    Element    Sample A    Sample B

    SiO2        49.50       49.20
    Al2O3       14.60       14.60
    Fe2O3        4.14        4.89
    FeO          7.53        6.18
    MgO          7.10        7.10
    CaO         11.60       11.60
    Na2O         2.50        2.50
    K2O          0.80        0.80
    TiO2         2.90        2.90
    MnO          0.18        0.18
    Total      100.85      100.58

Information Contacts: J. Lenat, OVPDLF; P. Bachelery, Univ. de la Réunion; A. Bonneville, Univ. du Languedoc; G. Boudon, Obs. Volc. de la Mt. Pelée; M. Halbwachs, Univ. de Chambéry; M. Kasser, IGN, Paris; A. Nercessian, IPGP, Paris; R. Vie le Sage, DRM, Paris.

07/1985 (SEAN 10:07) Intrusion E of the summit; lava production resumes a month later

"After the 24-hour eruption of 14-15 June, seismicity and deformation had returned to low levels. Sustained seismic activity began suddenly on 9 July. The intrusive seismic crisis, similar to the ones that have preceded all the outbreaks in the central area since 1981, continued until about 2250. The earthquakes were located between 1 and 2.5 km beneath the summit. The intrusion failed to reach the surface. The deformation pattern shown by the summit dry-tilt stations seems to indicate that the intrusion was emplaced E of the summit area.

"After declining for about 1 hour, the seismic activity resumed with a new swarm of earthquakes that were mostly centered 3-6 km WNW of the summit area at depths of 1-4 km. This crisis peaked on 10 July with more than 1,200 events, and progressively decreased during the following days. From 13 July to the end of the month the rate of seismicity decreased from 5-10 events/day to ~1 event/day.

"This second swarm is the first to be observed outside of the central area since the Observatory was established in 1980. It is also by far the largest recorded seismic crisis at Piton de la Fournaise. A large number of epicenters are also found along the 'Grandes Pentes' line which is the inland boundary of the 'Grand Brule' slump structure that is thought to result from the instability of the free flank of the volcano.

"On 5 August at 2250 a new intrusive seismic swarm began at shallow depth beneath the summit area and more than 200 events were recorded in less than 3 hours. An eruption started at 2340 N of the summit at the base of the central cone (E of Cratère Magne). Deformation related to this eruption affected the summit area and the descent to the Plaine des Osmondes, corresponding to a major inflation on both sides of a N-15°E fissure. From the beginning of the eruption until 9 August, 4 x 106 m3 of aphyric basalt have been emitted at a rate of 10-15 m3/s. Temperatures of 1,100-1,120°C have been recorded. The eruption was continuing as of 11 August."

Information Contacts: J. Lenat, H. Delorme and J. Delarue, OVPDLF; A. Hirn and J. Delattre, IPG, Paris; P. Bachelery, Univ. de la Réunion.

08/1985 (SEAN 10:08) Fissure activity resumes after 5-day hiatus

"The eruptive episode that began on 5 August ended 1 September. The major part of the aphyric basalt lava flow was emitted during the first 10 days. The lava front stayed at the bottom of the Grandes Pentes inside the Plaine des Osmondes (near the N caldera wall, figure 13). During the last week, small amounts of pahoehoe were emitted from tunnels at the foot of Cratère Faujas, about halfway between the central cone and the N caldera wall. Seismic tremor lasted for 10 days at a very low level.

Figure 13. Sketch map of the summit caldera region of Piton de la Fournaise after Blum and others (1981).

"Deformation related to the opening of the 5 August fissure affected the summit and the flank of the Plaine des Osmondes. No significant deformation was recorded during August, but minor summit deflation was noted around the fissure zone.

Information Contacts: H. Delorme and J. Delarue, OVPDLF; P. Bachelery, Univ. de la Réunion.

09/1985 (SEAN 10:09) Fissure eruption follows inflation and earthquake swarm

A very short seismic crisis began on 6 September at 1408. As for the June and August eruptive episodes, seismic events were centered under Dolomieu and Soufrière, at 1 km depth (10:5-8). After 30 shallow summit seismic events, three eruptive fissures opened at 1520. The first fissure (near Soufrière) was 50 m long and continued erupting for 2 hours. The second, 250 m long, opened inside the Dolomieu summit crater and erupted until 0500 the next morning. The third, E-oriented and 500 m long, opened on the E flank of Dolomieu (figure 14). [As of 7 September at 1400, the eruption was continuing from this fissure and the lava flow along the Grandes Pentes had reached 1,000 m altitude (10:08)].

Figure 14. Provisional map of the 1985 eruptive fissures and lava flows, as of 30 September. Courtesy of OVPDLF and the Université de la Réunion.

Eruptive activity was then limited to Dolomieu's E flank fissure at 2,200 m altitude. A major cone (Thierry crater) has formed, emitting lava that advanced to an altitude of 550 m, following 1977 flows. After a few days, active flow fronts reached only 1,700 m altitude, ~2 km from Thierry crater. The upper part of the fissure system was then reactivated 15-17 September, emitting a small amount of scoria and a small lava flow. Since 20 September, lava flows have been emitted through a tube at 1,900 m altitude. The volume of the lava was estimated to be 14-17 x 106 m3 of 30 September. The lavas are basalts with variable amounts of olivine phenocrysts. Major degassing took place, rich in sulfur compounds.

Before the 6 September eruption, a small summit inflation was recorded. Geodetic and leveling measurements show that horizontal and vertical deformation related to the new fissures reached 40 cm, coinciding with inflation of the E zone of Dolomieu. Deformation has been recorded in the whole W side of the Enclos caldera. During the eruption, no significant movement was recorded, except on the E coast.

Information Contacts: H. Delorme and J. Delarue, OVPDLF; P. Bachelery, Univ. de la Réunion.

10/1985 (SEAN 10:10) Deflation after lava production ends

"The eruption ended during the second week of October. After major lava extrusion in September, lava flows were emitted at low rates through a tube at 1800 m altitude [but 1900 in 10:9]. The total volume of lava for the September episode is estimated to be 17-20 x 106 m3. Degassing was very important, and eruptive cones were covered with sulfur deposits.

"Since the beginning of the month, a major deflation was detected on the E coast. This may correspond to the end of the inflation that began on 10 July (10:07). In mid-October, at the end of the eruption, this deflation was recorded both at the summit station and in the caldera. After some sporadic tremors, seismic activity associated with this eruption ended on 16 October."

Information Contacts: H. Delorme and J. Delarue, OVPDLF, Réunion; P. Bachelery, Univ. de la Réunion.

11/1985 (SEAN 10:11) Earthquake swarm then fissure eruption

"Seismic activity was very low during all of November and was at shallow depth (1-2 km) under the summit. Small deformation was measured only on the summit stations. Continuously-recording tiltmeters indicated progressive deformation on Bory Crater since 28 November.

"During the night of 1-2 December, a very short seismic crisis occurred. For 17 minutes, very shallow low-magnitude events occurred under Dolomieu crater at depths of 0.5-1.5 km. A 1.5-km fissure opened from the top of Bory crater down to the S flank of the central cone. This eruption lasted only 28 hours, from 2 December at 0215 to 3 December at 0600. The amount of basaltic lava emitted was very small.

"A major inflation pattern was recorded only on the summit stations. No deformation was found in the rest of the geodimeter net."

Information Contacts: H. Delorme and J. Delarue, OVPDLF; P. Bachelery, Univ. de la Réunion.

12/1985 (SEAN 10:12) Inflation, earthquake swarm, then summit crater fissure eruption

"After the very short (28-hour) eruption on 2 December, seismic activity was limited to very small shallow events in the summit zone for a few days.

"Since 25 December some deeper events have occurred under the summit zone (1-3 km depth). On the 28th two strong events (20 s) were recorded on the whole seismic network (11 stations) followed by a few events on the 29th. During the evening of the 28th very small events were noticed at the summit station, followed by a very short crisis (1836-50) and opening of fractures inside Dolomieu crater (1854-57). Aphyric basalt began to cover a large part of the crater floor (figure 15).

Figure 15. Map of the summit craters of Piton de la Fournaise as of 2 January 1986. Active fissures and lava flows produced since the beginning of the eruptive episode on 28 December 1985 are shown. Courtesy of OVPDLF.

"The opening of the fractures was sudden and rocks, cinder, and lava were ejected to heights of as much as 250 m. Lava fountains were 100-150 m high for one day, than activity was limited to one main cone (1 January). On 9 January, the main cone was still active, emitting important volumes of gases, mainly SO2. Lava temperatures were between 1,140° and 1,150°C. Some pahoehoe was observed in tubes.

"After the 2 December eruption, deformation indicated no relaxation of the summit area. From 6-27 December, a progressive deformation was recorded (30 µrad) on the Bory permanent tiltmeter. Tilt stations around the summit indicated a small summit inflation. The summit area and the S and W flanks of Bory were affected by deformation. Nothing has been detected anywhere else in the Enclos."

Information Contacts: H. Delorme and J. Delarue, OVPDLF; P. Bachelery, Univ. de la Réunion.

01/1986 (SEAN 11:01) Summit lava production continues

"The eruptive episode that began on 29 December inside the central (Dolomieu) crater (10:12) was still in progress on 31 January. The main cone, in the SW part of the crater (figure 16), reached a height of 40 m. Explosive activity was less important than during the first few days of the eruption. The vent emitted lava fountains to 20-50 m above the crater rim during the first weeks of January; afterward, fountains were limited to 15 m height. More than 95% of the crater floor has been covered by the new lava flow; maximum thickness was 20-25 m in the NE part of the crater. The total volume of the emitted lavas was ~7 x 106 m3 as of 30 January. All the lavas are aphyric basalts.

Figure 16. Map of the summit craters of Piton de la Fournaise as of 23 January 1986. Courtesy of the OVPDLF.

"Tilt stations around the summit craters indicated a general deflation (15-70 µrads) after the beginning of the eruption. No significant movement was recorded between 8 and 22 January. The plume was still very rich in SO2, and numerous fumaroles were found at the base of the main cone on top of the lava tubes.

"The seismic station close to Bory Crater (just W of Dolomieu Crater) was saturated during the whole month. The Soufrière station (300 m NNW of Dolomieu Crater) received significant signals from the tremor. This tremor has begun to decrease since 20 January on all stations except Bory. Major tremors affected the walls of the Dolomieu Crater, causing collapse and forming numerous cracks on the S rim and the rim between Bory and Dolomieu".

Reference. Blum, P., Gaulon, R., Lalanne, F., and Ruegg, J., 1981, Sur l'evidence de precurseurs de l'eruption du Piton de la Fournaise a la Réunion (Fevrier 1981): Comptes Rendus Acad. Sci. Paris, v. 292, serie II, p. 1449-1455.

Information Contacts: H. DeLorme and J-F. DeLarue, OVPDLF; P. Bachelery, Univ de la Réunion.

02/1986 (SEAN 11:02) Eruptive episode ends

The eruptive episode . . . ended on 7 February. Aphyric basalt lavas covered 95% of the floor of Dolomieu Crater. The volume of lava emitted is estimated to be 7 x 106 m3. Deflation was observed on the summit levelling stations in mid-February. A short seismic crisis occurred on 11-12 February; events were located E of the summit at 3 km depth. Since then seismic activity has returned to a very low level. Volcanic activity in 1985 is summarized in table 1. The total amount of lava emitted [in 1985] is estimated to be 33 x 106 m3.

Table 3. Summary of 1985 eruptive episodes at Piton de la Fournaise.

    Eruptive episodes in 1985

    Start Date     14 Jun   05 Aug    06 Sep    02 Dec    29 Dec
    Duration       24 hrs   4 weeks   6 weeks   28 hrs    6 weeks
    Lava volume       1        7         17       <=1         7
    (106 m3)

Information Contacts: H. DeLorme and J-F. DeLarue, OVPDLF; P. Bachelery, Univ de la Réunion.

03/1986 (SEAN 11:03) First eruption outside caldera since 1977; evacuations; pit crater formed

Eruptive activity resumed 19 March, after less than 6 weeks of quiet. This sixth episode of the eruption . . . included the first lava production outside the Enclos Caldera since 1977.

Pre-eruption seismicity and deformation. The first half of March was characterized by weak seismicity. On the l7th, intermediate-depth events began, centered 3 km below the summit. During the night and the next day, 7 events were recorded, all at the same depth, E of the summit zone. A seismic crisis began suddenly at 2246 and lasted 30 minutes without an eruption. All of the events were shallow and centered under the summit crater. A tiltmeter on the SW flank of Bory Crater and an extensiometer inside the crater recorded a sudden movement at 2245-2255 related to this intrusion. A 300-µrad inflation of the E portion of Dolomieu Crater was measured by the two tilt stations E of the summit area. Geodetic measurements between the Enclos Caldera and the summit showed a NW displacement of the E wall of Dolomieu. No movement was recorded within the caldera.

SE caldera eruption, 18-19 March. Significant seismic activity during the night of 18-19 March followed the intrusion and preceded fracturing that began in the S part of the caldera at 0500. An eruption began at 0640 in the SE part of the caldera (at the bottom of Nez Coupe du Tremblet; figure 17), producing lava fountains and a small flow from the 120°-trending fissure. The volume of lava erupted was low, and this phase ended at 1520. The seismic crisis, however, continued during the effusive activity with both deep (3-5 km) and summit events.

Figure 17. Map of Piton de la Fournaise showing the March 1986 eruption fissures, lava flows, and summit pit crater. Courtesy of P. Bachélery.

Upper flank eruption, 20-22 March. On 20 March at 0020 a weak tremor was recorded in the S part (near the Nez Coupe du Tremblet station), and outside the caldera. Observation of glowing lava was possible only during pre-dawn hours because of poor weather conditions and dense vegetation. Tremor increased during the night, and another 120°-trending fissure, 600 m long, opened outside the caldera at 1,000 m altitude (just above Piton Takamaka; figure 17). At 0900, authorities evacuated 250 inhabitants. Two lava flows issued from the fissure, cutting the main circum-island road (RN 2) in the afternoon (at 1500 and 1700) of the 20th. One moved N of Piton Takamaka and reached the sea the next day. The second flow passed S of Piton Takamaka, stopping 200 m from the sea. Significant seismic activity continued in the summit area during the flank eruption. Lava destroyed 8 houses, leaving 51 people homeless. The lavas are olivine basalts with a small amount of 1-4 mm olivine phenocrysts. Effusive and seismic activity continued at a high level through 21-22 March.

Lower flank eruption, 23-29 March.Seismicity increased on the 23rd at 0000, with numerous shallow seismic events in the summit area. More than 30 magnitude 1.5-2.7 shocks were recorded during the night. At 0900 a fissure opened in the circum-island road S of the volcano at < 100 m altitude (near Pointe de la Table) initially emitting only water vapor. At about 1600, the fissure apparently began to extend downslope into thick forest. At 1700, very viscous lava emerged from three vents (in the forest) at an altitude of 30 m. A levelling network established around the fissures showed the progressive emplacement of a shallow dike. A new tilt station 1 km away from the fissures did not record any movement.

The opening of the main fissures across the road reached 105 cm on 23 March (70 cm during the first 5 hours). After the onset of lava production, the width of the main fissure decreased by 9 cm, but widening resumed, reaching 129 cm on the 27th and 167 cm on the 31st. Right-lateral movement accompanying the opening of the fissures was measured at 41.5 cm the first day and 49.7 cm by the 31st.

During the night of 23-24 March, more vigorous activity took place between Pointe de la Table and the circum-island road. Predominantly pahoehoe lava emerged from lava tubes and cascaded into the sea at two points near Pointe de la Table. On the 24th seismicity decreased and was limited to the summit zone. Effusive activity stopped on the upper flank fissure (near Piton Takamaka) that had begun to erupt on 20 March, but significant degassing continued. Activity from the lower flank fissures was strongest on 24 March at about 1400. Outflow rates on the 24th exceeded 7 m3/s and lava temperature was 1,160°C. By the time lava production stopped on 29 March at 0100, 3-4 x 106 m3 of lava had built a very flat 30-hectare platform along the shore that contained many lava tubes. The lava front in the sea was ~1.5 km wide, and its maximum seaward extension was 150-200 m. The volume of degassed magma was ~5 x 106 m3. This flow was less olivine-rich than the Takamaka lava.

Summit eruption and pit crater formation, 29 March-5 April. On 28 March at 1000 a new seismic crisis began, with tremor on the dome at 1110-1120. The seismic crisis was limited to the summit area and lava emission stopped outside the Enclos caldera. No deformation had affected the summit area during the 20-28 March period, but on the 29th at 1030-1600, the tiltmeter on the SW flank of Bory crater recorded progressive summit deflation of 23 µrads. Seismicity changed at midday to tremor-like activity. At 2238 a phreatic explosion began in Dolomieu crater and minor fountaining occurred from a fissure in its SE sector. By early the next morning collapse had formed a pit crater 100 m in diameter and 80-100 m deep. Degassed lava emerged from just below one edge, perhaps from a sill or still-molten 29 December lava [see 11:4], forming a 5-m-wide cascade that drained back into the bottom of the newly formed pit crater.

A general deflation of 35-350 µrads of the summit area, centered on the SE part of Dolomieu Crater, occurred on the 30th. This deflation was not detected by the Enclos tilt stations. The summit lava flow stopped around 5 April.

Magnetic data. Beginning in mid-l985, a permanent magnetic network has been maintained on the volcano. Four stations telemetered to the observatory: Bory Crater (BOR), the N flank of the dome (PMC), the W part of the Enclos Caldera (CSR), and the observatory (PDC), with a 1-minute sampling frequency of the earth's magnetic field. The time variations of the simultaneous differences are studied with CSR as the reference station. Several days before the first seismic crisis (17 March), a slow decrease in the differences appeared, ~2 nanoteslas (nT)/10 days. Early in the seismic crisis of 17 March, a sharp decrease in the differences was observed (~3.5 nT and 2 nT for CSR and BOR). Similar variations were observed on the 29th when the seismic crisis preceded pit crater formation. By 3 April, after the eruptive episode, variations were no longer observed.

Further Reference. Delorme, H., Bachelery, P., Blum, P.A., Cheminée, J.-L., Delarue, J., Delmond, J., Hirn, A., Lepine, J., Vincent, P., and Zlotnicki, J., 1989, March 1986 eruptive episodes at Piton de la Fournaise volcano (Réunion Island): JVGR, V. 36, p. 199-208.

Information Contacts: H. DeLorme, J-F. DeLarue, J. Delmond, J. Hoarau, A. Hirn, J. Lepine, J. Zlotnicki, C. Robin (IGN), Hakenholtz (EDF), Maison (TAAF), and DuPont (ONF), OVPDLF, Réunion Island; P. Bachelery, Univ de la Réunion; P. Vincent and A. Bonneville, Univ de Clermont; J-L. Le Mouel, J-L. Cheminée, P. Blum, and G. Brandeis, IPGP; M. Krafft, Cernay, France.

04/1986 (SEAN 11:04) Collapse in summit zone

After the eruptive episode of late March-early April, seismic events were due primarily to collapse in the summit zone, especially inside Dolomieu Crater and in the walls of its newly formed pit crater. Some deeper events were recorded in the SE part of the Enclos Caldera at depths of 2 km below sea level. The lava that had cascaded into the pit crater 29 March-5 April was originally extruded during the 29 December eruption. Summit tilt stations indicated a continuation of low deflation. The SE flank fissures (~8 km from Dolomieu Crater, near Piton Takamaka) continued to emit vapor for a few days. Fumaroles, some emitting SO2, covered the floor of Dolomieu Crater. Reoccupation of the radial leveling profile (3 km long, from the Enclos Caldera rim to the summit) did not show significant movement since October 1985.

Information Contacts: H. DeLorme and J-F. DeLarue, OVPDLF; P. Bachelery, Univ de la Réunion; J-L. Le Mouel, J-L. Cheminée, A. Hirn, P.A. Blum, and J. Zlotnicki, IPGP.

06/1986 (SEAN 11:06) Brief eruption from March pit crater

A brief eruption occurred on 13 July between 1510 and 2110 [but see 11:7] from the bottom of the pit crater formed in March . . . . No activity had been reported since the end of the March-April eruptive episode . . . .

Information Contacts: J-L. Le Mouel and J-L. Cheminee, IPGP.

07/1986 (SEAN 11:07) Small pit crater eruption follows seismicity

"During June and July, seismic activity was semi-continuous. Shallow events, always located under the summit craters, were frequent (1-5/day). Some deep events (3-5 km) under the E part of the caldera were also noted but were less frequent. Since the end of May, some rare deeper events have been recorded, but were located less precisely.

"A small eruption occurred during the night of 13-14 July (between 1810 and 0010) after only two very shallow seismic events (at 1710, 500 m under the summit, M 1.1-1.5). A very minor amount of lava was emitted inside the 29 March pit crater. Small fountains produced 10-15,000 m3 of lava. Access to the lava is still prevented by continuous wall collapse of the 85-m-deep pit crater.

"Since the beginning of June, small tilt variations have been observed (maximum 24 µrads). The permanent tiltmeter network (Bory station on the summit and Chapelle in the caldera) recorded neither progressive nor irregular variations during the 10 previous days. After the eruption, seismic activity remained at a low level."

Information Contacts: H. Delorme and J-F. Delarue, OVPDLF; J-L. Le Mouel, J-.L. Cheminee, A. Hirn, P. Blum, and J. Zlotnicki, IPGP; J. Lenat, Centre des Recherches Volcanologiques and Observatoire de Physique du Globe de Clermont Ferrand.

11/1986 (SEAN 11:11) Ash eruption; lava from fissure

Ash and small quantities of lava were emitted from summit area vents in November and early December. Eruptive episodes were preceded by shallow fracturing from 18 September to about mid-November in the NE part of Dolomieu cone. Fracturing was indicated by weak seismicity detected only by summit stations. Tiltmeters recorded a slow, minor deflation. In early November, fracturing increased and was centered 700 m under the middle of Dolomieu. Geodetic measurements indicated that the E part of Dolomieu was sliding down to the ENE, accompanied by opening of the crater's N part. On 12 November, a very short, intense, seismic crisis (from 1150 to 1248) was followed by continuous tremor and a day-long ash eruption in the 29 March pit-crater. The crater floor rose nearly 40 m as 30,000-40,000 m3 of ash were emitted. Seismic instruments indicated that shallow fracturing continued after the eruption. Weak seismicity continued until 17 November.

Tremor in the S part of the (Enclos) caldera began on 15 November and lasted for almost two days. Beginning on 17 November, depth, frequency, and magnitudes of seismic events increased. Magnitudes were greater than 1.0 and hypocenters were at 1,500 m depth beneath the E part of Dolomieu Crater.

From 19 to 20 November a shallow seismic crisis shook the summit area and for the next six days 10-12 events/day were recorded. During the night of 25-26 November, M 2.0-2.5 events occurred ~3,500 m below Dolomieu Crater. The next evening (1530-1604), after 12 hours without seismicity or significant deformation, a 30-minute fracturing episode near the pit-crater (accompanied by tilt) marked the emplacement of magma. At 1604 an E-W fracture opened 200 m below the rim on the E flank, producing only a small amount of lava. After 30 hours of tremor, seismic activity remained weak, similar to the September-October shallow fracturing.

From 2 to 6 December a shallow seismic crisis occurred in the summit area, At 0700 on 6 December, a fissure eruption accompanied by tremor began in the bottom of Dolomieu Crater, where two vents and a fissure were observed. As of 15 December the eruption continued, as one vent emitted small quantities of lava and violent degassing events occurred from spatter cones. Intense seismicity was still being recorded at summit stations.

Information Contacts: H. Delorme, B. Gillet, and J. Delmond, OVPDLF; P. Bachelery, Univ de la Réunion; J-L. Le Mouel, J-L. Cheminee, A. Hirn, P. Blum, and J. Zlotnicki, IPGP.

12/1986 (SEAN 11:12) Lava from fissure fills pit crater

The eruptive activity on 26 November was followed by an increase in seismicity on 2 December, mainly centered below the summit crater (Dolomieu) at 700-1,500 m depth. The number of seismic events increased on 6 December at 0635, and half an hour later a N-S fracture opened in the W part of Dolomieu Crater, N of the 29 December 1985 cone. A second phase began 1 hour later (at 0803) inside the 29 March pit crater. Lava emanating from the fracture and a new cone in the SE part of Dolomieu filled the pit crater, already partially filled by 13 July and 12 November lava. Lava emission continued at a low rate but ceased from the initial fracture on 8 December. During December, almost 1.0 x 106 m3 of aphyric basalt was extruded onto the crater floor. The lava covered 2/3 of the floor with an average thickness of 1-2 m. Significant degassing accompanied the activity.

On 6 January, activity decreased in the four cones within Dolomieu and hornitos formed in the SE part of Dolomieu at the site of the lava-filled pit crater. The same day, a new eruptive phase began at the summit craters. Weak seismic events, barely detectable through the tremor, were recorded at summit stations beginning at 0855/0900. Seismicity was associated with strong deformation of the NE part of the summit of the Fournaise structure. At 1211, after eight summit events, a 700-m-long fracture opened on the slopes of the Osmondes Valley, NE of the summit, W of Piton de Crac, and very close to the April-May 1981 eruptive fissure. Lava flows and degassing were still being observed as of 15 January and the lava front had descended to 500 m altitude in the Grande Pentes region.

Information Contacts: H. Delorme and B. Gillet, OVPDLF; P. Bachelery, Univ de la Réunion; A. Hirn, J-L. Le Mouel, J-L. Cheminee, P. Blum, and J. Zlotnicki, IPGP.

05/1987 (SEAN 12:05) Seismicity, tilt, and summit intrusion

Low but constant seismicity was recorded from mid-April to early May, particularly in the N part of the volcano (12 April) and near the summit. Later in May, seismicity increased, and events remained shallow, below the two summit craters. Rare, deeper events were recorded in the E summit area. Progressive inflation had begun in April. Dry-tilt indicated an average inflation of 70 µrads around Bory Crater. Permanent inclinometers confirmed the dry-tilt data. Around 23 April inclinometers indicated that inflation had stabilized but a permanent magnetic station (6) showed a significant decrease, especially in the 7 x 11 km summit caldera. On 2 June at 1957 an intrusion occurred in the summit area accompanied by a seismic swarm lasting over 30 minutes. When seismicity ceased at 2030 no eruption had occurred.

Information Contacts: H. Delorme and B. Gillet, OVPDLF; P. Bachelery, Univ de la Réunion; A. Hirn, J-L. Le Mouel, J-L. Cheminee, P. Blum, and J. Zlotnicki, IPGP.

08/1987 (SEAN 12:08) Lava flows from summit crater

Seismicity beneath the summit continued after the 2 June intrusion. Minor inflation was recorded through 6 June. The volcano then remained stable until a new intrusion developed below the E summit zone at 0411 on 9 June. Seismicity ceased at 0500 but no eruption occurred. Hypocenters were concentrated along a N-S axis, 1-1.5 km under Dolomieu.

On 10 June, 50 µrads of inflation in the upper summit zone were recorded. At 1510 that day an eruption began in the S part of the crater along a 50-m N-S fissure. Lava broke out the next day in the E part of the crater (figure 18). About 106 m3 of aphyric basalt were extruded by 28 June. During this phase, two inflation pulses were recorded by the permanent tiltmeter network, on 18 and 22-26 June. After 28 June, moderate seismicity and slight deformation were recorded. Significant inflation was observed on 19 July from 0450 to 0630 during a new intrusion crisis, mainly in the NE part of Dolomieu. Seismicity shifted from N to S at about 0535. An eruption then occurred at two sites. The main eruption was 1 km S of the summit craters, close to Chateau-Fort (1948 eruption site), lasted ~32 hours, and produced slightly more than 106 m3 of aphyric basalt. Poor weather conditions prevented clear observation of the less-active site 1.5 km NNE of the summit. Deformation changes have not been significant since the eruptions, but weak summit-area seismicity began 15 August and was continuing in the first week of September.

Figure 18. Map of the summit area of Piton de la Fournaise showing 1987 lava flows. Courtesy of P. Bachélery.

Information Contacts: H. Delorme and B. Gillet, OVPDLF; P. Bachelery, Univ de la Réunion; J-L. Cheminee, A. Hirn, J. LePine, P. Blum, and J. Zlotnicki, IPGP.

11/1987 (SEAN 12:11) New fissure eruptions

An increase in seismicity began 3 November, associated with weak inflation NE of Dolomieu summit crater. An eruptive phase followed on 6 November at 2111, on the N flank of the cone. After a discernable decrease in tremor and continuing seismic activity, a second eruptive phase was registered at 2147. Activity lasted until about 2330. During these two phases, a series of three fractures had opened ~1 km N of Dolomieu. The main aa flow had stopped advancing by the time a new fissure opened at 0040 on 7 November, 1 km NE of the earlier fissures. About 1.6 x 106 m3 of aphyric basalt had been extruded by the end of all activity at 0600 on 8 November.

On 29 November an earthquake swarm of ~20 events was recorded. An eruption began the next day when a new fissure opened at 0805 in Enclos Caldera S of the central cone. A second fissure opened at 0932. On 1 December, there was moderate activity during a single event and weak tremor.

Information Contacts: P. Bachélery, Univ de la Réunion; OVPDLF (translated from a report in LAVE Bulletin no. 11).

12/1987 (SEAN 12:12) Lava flows from fissures and tubes

The small eruptive episodes of 6-7 November 1987 . . . produced <1 x 106 m3 of aphyric basalt. For the rest of the month, seismicity remained strong and at shallow depth below the NE part of the summit cone. A progressive increase in the number of these low-magnitude events during the second half of the month was accompanied by slight deformation in the E summit zone.

On 29 November, a very shallow seismic crisis began, accompanied by much fracturing. From 0630 the next day, seismic events were well-localized in the NE part of Dolomieu summit crater. The seismic record from the summit network was saturated between 0720 and 0750, when most of the deformation was recorded by the tilt network. At 0803, after a slight displacement of the seismicity and deformation, the first fissure opened at the S base of the central cone (2,240 m elevation). At 0932, three new fissures 100-200 m long and oriented N10°W, opened in the S part of the caldera, near the 1972 vents. Lava came mainly from the S-most fissure at 1,920 m elevation. Magnetic observations correlated well with the crisis.

Between 20 and 24 December, tremor completely ceased for 5-30-minute periods. Slight inflation (3-20 µrads) of the S flanks of the summit cone preceded new tremor, and explosions and deflation followed. On the 24th a more significant inflation of 25 µrads remained and there were no variations in tremor. Field observations were very well correlated with the tremor variations. After seven days of low-amplitude tremor, eruptive activity ended on 1 January at 1400. The accumulated inflation remained in the S part of the cone.

From 30 November to 24 December, ~6-8 x 106 m3 of aphyric basalt was carried through tubes and emitted in the S part of Enclos Caldera. Flows reached the S wall of the caldera.

Information Contacts: H. Delorme, D. Vandamme, and P. Nerbusson, OVPDLF; P. Bachelery, Univ de la Réunion; J-L. Cheminee, J. Dubois, A. Hirn, J. LePine, J. Zlotnicki, and P. Blum, IPGP.

01/1988 (SEAN 13:01) Strong seismicity then fissure eruption

A total of ~7 x 106 m3 of aphyric basalt was extruded in the 30 November-1 January fissure eruption. Throughout January seismicity was low and limited to rare events under the summit area. Deformation was insignificant. Strong seismicity began again on 4 February, when two deep events occurred E of the central cone. A brief but intense seismic crisis followed on 7 February between 2032 and 2220. Three events of M 2 were registered. An eruption phase began at 2240, as lava flows emerged from three fissures that opened in the S part of Enclos Caldera, close to the recent vents (S of Chateau-Fort Crater) and in the same region as the 1972 vents.

Information Contacts: H. Delorme, D. Vandamme, and P. Nerbusson, OVPDLF; P. Bachelery, Univ de la Réunion; J-L. Cheminee, J. Dubois, A. Hirn, J. LePine, J. Zlotnicki, and P. Blum, IPGP.

02/1988 (SEAN 13:02) Lava production, tremor, and deformation

The fissure eruption continued through early March, but the rate of lava production was very low. From 7 to 15 February, sizeable lava fountains were erupted, then lava flows were observed, accompanied by limited deflation of the S flank of the central cone. Since 15 February, strong variations in tremor have been well-correlated with fluctuations in the south-lateral tilt stations (Bory), as during the 30 November-1 January eruption. No simultaneous discrete seismic events were recorded. As of 14 March, tremor continued to be recorded at a very low level. No eruptive activity was visible other than a sulfur-rich plume from the new 20-m-high cone.

Information Contacts: H. Delorme, D. Vandamme, and P. Nerbusson, OVPDLF; P. Bachelery, Univ de la Réunion; J. Dubois, J-L. Cheminee, A. Hirn, P. Blum, and J. Zlotnicki, IPGP.

05/1988 (SEAN 13:05) Intrusion, then lava from fissure vents

The fissure eruption . . . stopped on 2 April. A well-documented intrusion preceded a large N-flank fissure eruption that began on 18 May and was continuing on 10 June.

Seismicity was weak and shallow during April. Around 15 April, after weak summit inflation recorded on the permanent telemetered tilt network (5-minute frequency), rapid but limited inflation was noted in the E summit area, accompanied by magnetic variations. On 20 April at 0700, there was a 30-minute seismic crisis (in the NE part of the summit at 1,500-1,200 m altitude) that was not followed by an eruption. Inflation was confirmed during the following days, but stopped.

After three weeks of minor shallow seismicity without significant variations in deformation, two shallow M 1.2 events were recorded on 17 May, again in the NE part of the central cone. A brief, shallow (100-1,500 m altitude) seismic crisis began the next morning at 0403. Magnitudes did not exceed 2.0. Deformation began 6 minutes later, at 0409, recorded by three tilt stations and one strainmeter (Soufrière). Inflation of the upper part of the central cone, in the SE sector of Dolomieu Crater, could be correlated with the onset of a shallow intrusion (500-700 m altitude). At 0420, inflation was increasing and was displaced to higher altitude (around 500-700 m). Between 0420 and 0425, inflation stabilized in the SE part of the crater then suddenly was displaced rapidly to the N out of Dolomieu Crater. Summit deflation was recorded by three tilt stations (figure 19), and compression was measured across the fissure monitored by the Soufrière strainmeter, confirming the migration of the deformation and anticipating the position of the eruptive vents. Magnetic variations were recorded at some stations.

Figure 19. Progressive deformation recorded by the Soufrière and Bory tilt stations as the intrusion migrated from the summit region toward the eventual eruption fissures early 18 May 1988. Courtesy of OVPDLF.

At 0433, fissures opened in four stages from 2,200 to 1,900 m altitude, E of the 7 November 1987 fissure vents (near von Drasche and Faujas Craters). The lower part of the fissures was initially very active, with large fountains of aphyric basalt emerging from a principal 300-m-long spatter rampart. Significant lava flows were extruded during the first 3 days of the eruption, and flow rates of up to 40 m3/s were observed. Lava production certainly exceeded 15 x 106 m3 during the first week, then flow rates declined to an average of 12 m3/s. The activity built a new cone, 25 m high, named Durandal (figure 20). Lava production from Durandal's crater stopped after 12 days, but lava continued to pour from tubes at the base of the cone (where there was a 10-m-high tumulus) advancing down the slopes of the Osmondes valley and accumulating as far as the base of the Piton de Crac, 3 km from the vent.

Figure 20. Sketch map showing part of the summit caldera of Piton de la Fournaise. The May 1988 and November 1987 lava flows are indicated by diagonal shading. Durandal Crater and fissure vents active in the 1988 eruption are shown with heavy lines. Courtesy of OVPDLF.

Continuous E flank deflation had been recorded since the beginning of the eruption, with deformation returning progressively to its pre-eruption status. On 3 June deflation stopped; after a brief calm, a vent opened at the base of Durandal Crater, feeding a high-temperature lava flow. Activity was continuing as of 10 June, with the emission of a small degassed lava flow at a low rate, occasional tephra ejections, and significant sulfur degassing from Durandal Crater. Total lava production was estimated at around 30 x 106 m3, and the eruption was considered as one of the most important of the last 10 years.

Information Contacts: H. Delorme, D. Vandamme, P. Nerbusson, J. Delmond, and P. Taochi, OVPDLF; J. Dubois, J-L. Cheminée, A. Hirn, P. Blum, and J. Zlotnicki, IPGP ; P. Bachelery, Univ de la Réunion.

07/1988 (SEAN 13:07) Minor lava production; deflation stops

The N-flank fissure eruption was continuing at a low level on 26 July. Occasional tephra ejections stopped 1 July but degassed lava remained in Durandal crater to roughly 15-20 m below the rim. Lava drained directly into tubes and surfaced in the Plaine des Osmondes, > 1 km downslope. Little change in lava flow volume has occurred since 10 June. Harmonic tremor continued at a low level except at Soufrière station, just NE of the summit, where continuous NE-flank deflation had been recorded by tilt stations since the eruption's onset. Deflation progressively decreased before stopping on 12 July. Average rates were 8 µrads/day 18-24 May, 3.5 µrads/day 25 May-3 June, and 1.7 µrads/day after 4 June. There were no significant changes in the magnetic data.

Information Contacts: H. Delorme, D. Vandamme, P. Nerbusson, J. Delmond, and P. Taochi, OVPDLF; J. Dubois, J-L. Cheminée, A. Hirn, P. Blum, and J. Zlotnicki, IPGP ; P. Bachelery, Univ de la Réunion.

09/1988 (SEAN 13:09) Deformation precedes fissure eruption

During most of August, only weak summit-area microseismicity was detected. Permanent tiltmeter stations recorded inflation of a few µrads/week, similar to previous months. Seismicity increased in late August, and on the 31st at 1523, deformation measurements documented the onset of magma intrusion into the SE part of the summit (Dolomieu) crater. As the intrusion migrated W during the following 2.5 hours, tilt data provided good location estimates of the initial eruption fissures. These began to open at 1748, on the SW flank of neighboring Bory crater, and gradually propagated downslope from 2,250 to 2,150 m altitude (S of Rivals Crater and E of December 1983 Crater). Aphyric basalt extrusion was significant during the first 5 days and then declined until ceasing around 10 September [but see 13:11]. Lava production was <4 x 106 m3. Since the eruption, activity has been limited to strong degassing and continuous weak tremor.

During September, deep earthquakes (30-50 km) were recorded NW of the volcano between Piton de la Fournaise and Piton des Neiges. One event (M 3.0) was felt by the population in the "Cirque de Mafate" and in the N island area.

Information Contacts: H. Delorme, D. Vandamme, P. Nerbusson, J. Delmond, and P. Taochi, OVPDLF; J. Dubois, J-L. Cheminee, P. Blum, A. Hirn, J. LePine, J. Zlotnicki, IPGP.

11/1988 (SEAN 13:11) New fissure eruption follows seismicity and deformation

Deformation and a brief seismic swarm preceded a new fissure eruption on 14 December. Lava production from the fissure eruption that began 31 August had stopped on 12 September. Strong degassing continued until early October. Between September and mid-December, the permanent telemetered EDM (5-minute period) recorded 5 cm expansion of the summit crater, associated with fissure extension measured by strainmeters. Radial tiltmeters detected no significant changes. Seismicity remained weak until 12 November, when 25 minutes of low-energy summit seismicity was recorded, without associated deformation. Since then, discrete shallow events had increased in the summit area.

On 14 December at 0830, a seismic crisis began that included both shallow and deeper events in the summit area. Deformation indicated northward magma migration between 0850 and 0910. The seismic crisis continued until 1220, when low-frequency tremor appeared on the summit seismic station (SFR). At 1306 [but see 13:12], an eruptive fissure opened in the N part of the Enclos Caldera, ~400 m E of the August 1985 crater. Three main NNE-trending, en-echelon fissures developed between 1,900 and 2,050 m elevation, and at 1400 a fissure opened just above them.

Information Contacts: H. Delorme, P. Nerbusson, D. Vandamme, J. Delmond, and P. Taochi, OVPDLF; P. Bachelery, Univ de la Réunion; J. Dubois, J-L. Cheminée, A. Hirn, J. LePine; P. Blum, and J. Zlotnicki, IPGP.

12/1988 (SEAN 13:12) Fissure eruption in N part of caldera

The onset of the 14 December eruption, at 1303, followed 40 minutes of 1-Hz tremor. Data from the tilt network had allowed geologists to reach the field 2 hours earlier and provided an excellent forecast of vent location. Geologists heard (and saw through clouds) the opening of a 400-m fissure N of Faujas Crater that ejected 20-50-m fountains of aphyric basalt and built a new cone. A second fissure opened to the SW, but lava production was low. During the following days, a significant number of discrete seismic events accompanied vigorous tremor. Most seismic events were limited to the summit zone, but some were recorded in the N part of the caldera. Eruptive activity stopped suddenly on 29 December at 0150. Since then, seismic activity has progressively resumed.

Information Contacts: H. Delorme, P. Nerbusson, D. Vandamme, J. Delmond, and P. Taochi, OVPDLF; P. Bachelery, Univ de la Réunion; J. Dubois, J-L. Cheminée, A. Hirn, J. LePine; P. Blum, and J. Zlotnicki, IPGP.

01/1990 (BGVN 15:01) Nineteen hours of lava fountaining from central crater fissure after 3 months of seismicity

[This preliminary report is supplemented by detailed information in 15:2]. An eruption began on 18 January at 1124 from the SE area of the central (Dolomieu) crater and from its upper SE flank. The eruption was preceded by three months of significant seismicity. Vigorous 50-100-m fountaining from roughly NW-SE-trending fractures was observed until about 1500. Activity had completely stopped by 0630 on 19 January.

Information Contacts: J. Toutain, P. Taochi, J-L. Cheminée, IPGP; P. Bachelery, Univ de la Réunion.

02/1990 (BGVN 15:02) Lava fountains and flows from summit-area fissure, with seismicity and deformation

Both short- and long-period seismic events were recorded in the months preceding the eruption. Most were located below the summit, with some below the volcano's E flank (Grandes Pentes area). Three seismic swarms, each with >25 shocks, occurred in September and October, but no deformation or surface changes were noted. The number of seismic events (figure 21) increased in the days before the eruption, with 32 and 69 shocks recorded on 16 and 17 January respectively, centered below the N flank of Dolomieu Crater (figure 22).

Figure 21. Seismic events at Piton de la Fournaise, 10-20 January 1990.
Figure 22. Epicenter map showing times of located earthquakes (top) and cross-section showing focal depths of the same earthquakes (bottom) during the 17-18 January 1990 pre-eruption seismic crisis at Piton de la Fournaise. 17 January events are labeled in italics, 18 January events in regular type.

The eruptive crisis began at 0322 with a 4-5-minute swarm of 33 events. Seismicity then decreased until 1036, when a new swarm of short-period earthquakes (lasting 2-5 seconds with events ~15 seconds apart) was recorded. Deformation (figure 23) was observed from 1032 until 1052 at the Soufrière and Dolomieu tilt stations (7 and 19 µrads respectively), suggesting inflation centered on Dolomieu Crater. An 11-second shock was detected at 1048, followed by a new swarm recorded by the summit stations. Numerous collapses of the Dolomieu crater rim were observed, especially on the NE rim. From 1052 to 1112 a clear deflation pattern (45 µrads) through Dolomieu Crater was detected by the Soufrière tiltmeters, whereas the Dolomieu tiltmeters (on the S edge of Dolomieu Crater) suggested tilt towards the SW. Events of the second swarm were at first generally centered below Dolomieu's NE flank (1038-1042), then succeeding events moved below the SE flank. All were very shallow, the deepest ~1 km asl.

Figure 23. Deformation data from the continuously recording Soufriere tiltmeter at Piton de la Fournaise, 18 February 1990. Numbers correspond to the following phases of the activity: 1) Seismic swarm; onset of inflation, centered below Dolomieu crater. 2) Beginning of magma injection. 3) Beginning of tremor. 4) Lava output. 5) Beginning of fissure migration towards the N. Deformation values in the text have been corrected for temperature effects.

Tremor appeared at 1112 on summit stations, with discrete shocks continuing until 1120. Maximum tremor intensity occurred at approximately 1124, while Soufrière tiltmeters recorded a 58 µrad tilt toward the NNW, and Dolomieu tiltmeters recorded a >100 µrad tilt toward the NE. These seismic and deformation signals coincided with the opening of an eruptive fissure in Dolomieu Crater, seen at 1124 by geologists making distance measurements in the summit area.

The fissure trended roughly N170°E, feeding vigorous lava fountains ~30 m high, and mainly aa flows that covered roughly 20% of Dolomieu's crater floor. The fissure rapidly propagated S towards Dolomieu's crater rim, then towards Maillard crater (figure 24). Lava fountains also occurred from the fissure extension, and lava emerged from the base of Maillard crater. After reaching Maillard Crater, the fissure progressively migrated NNW within Dolomieu Crater, to near the N crater rim. Fissure migration was accompanied by local SW tilting, recorded by the Soufrière station, whereas no significant motion was detected by Dolomieu tiltmeters. Eruptive spatter cones were aligned along this section of the fissure, which produced strong gas emissions and ejected lava fragments. Tremor remained at a significant level until 1730, then progressively decreased. Another seismic swarm occurred at 0244 before tremor ceased completely at 0630 on 19 January.

Figure 24. Sketch map of the summit area at Piton de la Fournaise, showing the lava flows, main fractures, and the approximate positions of the Soufriere and Dolomieu tilt stations.

During this brief eruption (~17 hours), <1 x 106 m3 of aphyric lava was emitted, with a mean calculated lava output rate of ~14 m3/s. Geologists noted that geodetic measurements could be interpreted in terms of an E-dipping dike injection.

Information Contacts: J. Toutain and P. Taochy, OVPDLF; P. Bachelery, Univ de la Reunion; J-L. Cheminée, IPGP. Field observations are from P. Kowalski, A. Mussard, P. Piquemal, and P. Taochy (OVPDLF), P. Mairine, and A. Talibart.

04/1990 (BGVN 15:04) Lava production from summit caldera follows five days of increased seismicity

After ~15 days of increased seismicity, an eruption began on 18 April at 1252. Lava production occurred from the SE part of the Enclos Fouqué caldera, with vigorous fountains (~30-50 m high) that built the "Catherine N" eruptive crater, and extrusion of flows that advanced down the Grand Brûlé area. Poor weather during the eruption severely hampered observations.

Information Contacts: J-P. Toutain and P. Taochy, OVPDLF; P. Bachelery, Univ de la Réunion; J-L. Cheminée, IPGP.

05/1990 (BGVN 15:05) Dike injection, then eruption from fissure vents near S caldera wall

The following supplements 15:4. After ~15 days of increased seismicity (figure 25) an eruption began on 18 April at 1250. That morning, four low-energy (duration <10 seconds) summit earthquakes were detected between 0605 and 0654. At 0706, seismic activity increased suddenly, and a swarm of ~40 events, most with durations of 5-35 seconds, occurred within 20 minutes. A summit seismic crisis began at 0726, with almost continuous summit shocks (roughly every 10 seconds).

Figure 25. Number of earthquakes (top) and daily seismic energy release (bottom) at Piton de la Fournaise, June 1989-April 1990.

Summit-area tilt stations began to record considerable deformation at about 0730. Geologists used tilt vectors from the three summit stations to estimate the position of the inflation center, and documented its migration at 1- or 5-minute intervals, depending on the intensity of deformation (figure 26). Deformation centers seemed to be located below the E part of Dolomieu Crater from 0730 to 0745, then migrated rapidly SE from 0745 to 0751, at a calculated velocity of ~2.3 m/s, probably related to dike injection. Deformation then appeared to reverse to a general summit deflation as the dike continued to move SE.

Figure 26. Map of the summit area of Piton de la Fournaise showing migration of the inflation center, calculated using tilt vectors from the Dolomieu, Bory, and Soufriere stations.

The intensity of the summit seismic crisis decreased at 0759, and most of the recorded events had progressively lower frequencies, with the last typical high-frequency shock recorded at 0803. Low-frequency seismicity continued until 1250, associated after 1142 with four high-frequency shocks. One of the latter (at 1151) was centered in the Grandes Pentes area. Generalized tremor indicated that eruptive vents opened at 1250, but poor weather prevented any direct observations.

Geologists from the OVPDLF and the Univ de la Réunion arrived at the eruption site the next day at about 1100. A new fissure ~150 m long, trending roughly 170°, included about five small spatter cones 5-10 m high, but none of the vents remained active. Vigorous lava fountaining, 30-50 m high, was occurring from a cone ~30 m high (Catherine N. Crater, figure 27) at the S end of the fissure. A lava lake was visible inside the crater, feeding flows into two main channels at an estimated output rate of 20-30 m3/s. Temperature of the lava 30 m downslope was ~1,110°C. Lava flowed onto the Grand Brûlé area, covering 0.925 x 106 m2 with a calculated volume of ~ 5 x 106 m3 by the 20th. This yielded an average output rate of 19 m3/s, in general agreement with field estimates. By the end of the eruption, lava covered a surface area of 1.52 x 106 m2 with a volume of 8 x 106 m3. The lava was an aphyric basalt that appeared identical to products of the 18-19 January eruption.

Figure 27. Sketch map of the Enclos Fouque caldera at Piton de la Fournaise, showing Catherine N. crater and the area covered by April-May 1990 lava. Filled circles mark tilt stations, open circles with stars indicate magnetic stations.

SO2 degassing from Catherine N. Crater was observed and aerosols were collected, but no high-temperature vents could be accessed for direct magmatic gas sampling. Magnetic changes were also associated with the eruption. Mean daily magnetic intensity differences between a station on the N flank of Dolomieu Crater (PMC) and a reference station (CSR) showed a clear decreasing trend.

Tremor decreased during the morning of 19 April to about half of the previous day's values, and remained at a low level after the 20th. On 25 April, lava fountains were considerably lower (~10 m high) and lava output rate was very low. Because of the decreasing output rate, lava flowed into tubes, emerging 0.5-1 km downslope. The eruption stopped on 8 May at about 2300.

Information Contacts: J-P. Toutain and P. Taochy, OVPDLF; P. Bachelery, Univ de la Réunion; J-L. Cheminée, IPGP; observations and data interpretation were also carried out by L. Fontaine, P. Kowalski, A. Legros, E. Piquot, and P. Piquemal, and field support was provided by A. Gerente.

07/1991 (BGVN 16:07) Brief lava production follows seismicity, deformation, and magnetic changes

A short eruption occurred on 19-20 July, following a slight increase in seismicity that began 24 June (figure 28), and immediately preceded by a shallow microearthquake swarm. Almost 80 earthquakes (M <1.5), located beneath the S flank of the summit cone at depths of <1 km, were recorded from 0256 to 0350 on 19 June. At 0350, the appearance of tremor signaled the start of lava outflow.

Figure 28. Daily number of earthquakes (top), measured tilt at Dolomieu station 100 m S of the crater (middle), and difference of magnetic field from the reference station 3.5 km W of the fissure (bottom) at Piton de la Fournaise, 30 May-19 July 1991. Courtesy of J. Toutain.

EDM (sampled every 5 minutes) and radial tilt measurements (every minute) at a station (DOLO) ~200 m from the eruptive fissure (figure 29) showed relatively slow inflation beginning at 0310 (figure 30), believed associated with the beginning of intrusion from the magma reservoir. At 0340, radial tilt began to increase rapidly (up to 54 µrad/min), while EDM indicated a rapid decrease in the distance between the rims of the two summit craters. Inflation led to southward tilting (mean azimuth, 175°) of the DOLO station area. Rapid deflation began at 0350, corresponding with the start of tremor, and lasted until 0434. Deflation occurred at maximum rates of 48 µrad/min, causing DOLO to tilt roughly N (azimuth ~10°).

Figure 29. Sketch map showing the summit area of Piton de la Fournaise and the 19 July 1991 lava flows. Courtesy of J.P. Toutain.
Figure 30. Deformation at Piton de la Fournaise, 0140-0500 on 19 July 1991. Top: EDM, sampled every 5 minutes at Dolomieu. Middle: tilt measurements, sampled every minute at Dolomieu and Soufriere; bold lines=radial component, normal lines=tangential component. Bottom: measured strain, sampled every minute at Dolomieu; Z=vertical, X and Y= horizontal components. Arrow indicates start of eruption. Stations are shown in Figure 33. Courtesy of J. Toutain.

The magnetic field near the eruptive vents (station 6) showed a clear decreasing trend beginning on 16 June (figure 28). On 19 July, a rapid magnetic field increase was measured, corresponding with the onset of the eruption.

Lava was emitted from two vents along an eruptive fissure, one inside and one outside of the summit (Dolomieu) crater (figure 29). Lava fountains, 30 m high, were observed during the morning of the 19th and flow velocity was estimated at 3-4 m/sec that afternoon. Lava flowed E through the Grandes Pentes area, covering ~ 1 x 106 m2, with a total volume estimated at 5 x 106 m3. The eruption lasted until about 2000 on 20 July.

Information Contacts: J. Toutain and P. Taochy, OVPDLF; P. Bachelery, Univ de la Réunion; J-L. Cheminée, P. Blum, A. Hirn, J. LePine, and J. Zlotnicki, IPGP; F. Garner and I. Appora, Univ Paris VI.

09/1992 (BGVN 17:09) Summit fissure eruption follows 7 months of seismicity

An eruption began on 27 August after 7 months of increased seismicity below the summit crater and the E flank of the summit cone. Up to 19 earthquakes/day were recorded during the days before the eruption (figure 31). Focal depths were from about sea level to 1.5 km altitude . . . . (figure 32).

Figure 31. Daily number of earthquakes at Piton de la Fournaise, January-August 1992. A white arrow marks the start of the eruption. Courtesy of OVPDLF.
Figure 32. Epicenters of seismic events at Piton de la Fournaise, 2-26 August 1992, with N-S and E-W hypocentral cross-sections. A sawtooth pattern marks the rim of Enclos Fouque caldera. The epicenter map's location is indicated by the small rectangle on the inset map. Courtesy of OVPDLF.

Immediate eruption precursors - seismicity. A shock at 1054 on 27 August marked the onset of the pre-eruption seismic crisis. About 30 events of up to M 1.3 were detected between then and the swarm's strongest shock (M 2.2) at 1105. More than 100 seismic events of M >1.3 followed until 1150, when generalized tremor indicated the start of the eruption. Hypocenters were beneath the E part of the Dolomieu Crater between the summit and sea level. Geologists interpreted the seismic pattern as resulting from a shallow magma pocket feeding an intrusion moving up towards the Dolomieu area.

Immediate eruption precursors - deformation. Rapid changes in vertical ground deformation began less than an hour before the eruption at electronic tiltmeters between the Dolomieu crater rim and sites 8 and 9 km away. The maximum radial component of 1,300 µrad was recorded on the SE side of the crater (station DOL, figure 33). Less deformation (<=20 µrad, tangential) was detected 1.5-2 km away, and at 8 and 9 km the deformation was 0.8 µrad (radial) and 7 µrad (tangential), respectively. At stations around the crater rim, tilt values (3, 10, and 12 µrad/minute at BOR, SOU, and DOL, respectively) and directions from 1111 to 1124 indicated inflation centers and possible intrusion below the SW part of the crater (figure 33). Tilt values increased between 1125 and 1133 to 5, 10, and 30 µrad/minute, respectively, with NW tilts at BOR and SOU, and a SE tilt at DOL. This pattern suggested a general inflation of Dolomieu, but inflation centers could not be identified. The period 1134-1139 was similar, with the highest tilt at DOL. During 1140-1145, tilt vectors rotated at SOU and BOR while the radial component at DOL inverted. This period is interpreted by geologists as a deflation episode. Deformation stopped after 1145 at the BOR and SOU stations, but continued until 1155 at DOL.

Figure 33. Map of the summit area of Piton de la Fournaise, showing tilt vectors at BOR, SOU, and DOL stations for six time-periods on 27 August; the first five periods begin at 1111, 1125, 1134, 1140, and 1146. Tilt vectors could not be calculated at DOL after 1134. Inflation centers calculated from tilt vectors are indicated by triangles enclosed by the dashed line. Hachures mark the rims of Bory and Dolomieu craters. Courtesy of OVPDLF.

Eruptive activity. The eruption began at 1150 from a fissure within Dolomieu crater that produced lava fountains ~40 m high and a small basaltic lava flow. The fissure propagated rapidly southward, crossed the SW rim, and produced a small flank flow (flow 1; figure 34). Four additional vents opened at 1211, 1214, 1216, and 1221, producing lava flows 2-5. The first four flows halted within 3 hours, but high lava fountains (>40 m) at vent 5, SE of Dolomieu crater, quickly built a cone, named Zoé. The high velocity of flow 5 and strong degassing were noted 3 hours after the start of the eruption. Geologists from the OVPDLF reported 40-m lava fountains and intense SO2-rich degassing on 28 August. Flow velocity at the foot of the cone was estimated at 4 m/s, suggesting a mean outflow rate of ~20 m3/s. Geologists estimated that Zoé crater produced 5 x 106 m3 of lava, covering ~1 x 106 m2. Flows 1-4 included an additional 5 x 105 m3 of aphyric basalt. Tremor decreased rapidly and had reached low levels by mid-September. Tremor ceased on 23 September after ~20 hours of strong seismic activity related to the collapse of the main crater and surface feeding structures. Outflow was very weak during the eruption's last days, and the total volume of lava remained at 5.5 x 106 m3.

Figure 34. Sketch map of the southern part of Enclos Fouque caldera on Piton de la Fournaise, showing Zoe Crater and the area covered by the five successive lava flows on 27 August 1992. The area shown is indicated by the small rectangle on the inset map. Courtesy of OVPDLF.

Information Contacts: J. Toutain, P. Kowalski, P. Labazuy, P. Taochy, A. Tessier, and A. Pham, OVPDLF; J-L. Cheminée, P. Blum, J. Zlotnicki, A. Hirn, and J. Lepine, IPGP.

12/1996 (BGVN 21:12) November intrusion signaled by radon and geophysical measurements

During the last four years, quiet prevailed at Piton de la Fournaise (figure 35), with unusually low seismic activity and no eruptions. During late November, however, scientists at the Observatoire Volcanologique du Piton de la Fournaise noted an increase in radon flux followed a day later by an increase in seismicity. This also accompanied changes in tilt, local extension, and larger-scale distance movements. These observations led the scientists to infer that there had been a magma intrusion.

Figure 35. Sketch map of Piton de la Fournaise and vicinity showing the locations of observation stations. Notice that the topographic contour intervals on this map are uneven. Courtesy of OVPDLF.

Seismicity. In September a 16-km-deep swarm of earthquakes was recorded ~5 km NW of the summit. Seismicity continued to increase under the summit, and a M 2.3 event was registered on 18 October. A short but intense seismic crisis (figure 36), which began at 2126 on 26 November, consisted of 134 registered events. Among them, there were 37 earthquakes larger than M 1 and two in the range of M 2-2.4. The strongest one took place at 2149, an event nearly coincident with changes recorded by inclinometers and extensometers and inferred to correspond to the beginning of the principal magma movement. The seismic activity decreased at 2220 and ended with a final event of M 1.9 at 2310. After that, seismicity remained low. All events during this seismic crisis originated at about sea level ( ~2.5 km below the summit) at the Soufrière region, slightly N of the summit.

Figure 36. Cumulative seismic moment during January-November 1996 at Piton de la Fournaise. Thin dotted line shows cumulative seismic moment under the summit; heavier line represents volcano-wide cumulative seismic moment minus the cumulative seismic moment under the summit. Courtesy of OVPDLF.

Tilt and extension. Although not shown in figure 37, a small amount of ground movement might have taken place prior to the prominent tilt event at about 2149 on 26 November. The tilt accompanied inflation of the summit region, and tilts of 16, 8, and 4 µrad were recorded at stations Soufrière, Dolomieu, and Bory, respectively. Stations Chapelle and Chateau Fort at the base of the cone tilted <1 µrad. Displacements of <0.1 mm were also recorded by extensometers at stations Magne, Chateau Fort, Soufrière, and Dolomieu.

Figure 37. Tilts at stations Bory, Soufriére, and Dolomieu at Piton de la Fournaise. "Rad" and "tgt" refer to radial and tangential components, respectively. Courtesy of OVPDLF.

Distance change. Distances between station Piton Partage and different prisms on the cone were measured automatically by a TM3000 instrument (figure 38). During 25-26 November, a decrease up to 10 mm occurred for prisms on the profile between Soufrière and Puy Mi-Cote (prisms 1M20, 2M54, 2M53, 2M52, 2M42, and 1M40). In addition, the distance decreased slightly for one prism at Magne (2M26); no distance change was observed for the prisms between Chapelle and Bory and for one prism at the E side of the cone (2M31).

Figure 38. Distance changes between station Piton Partage and different prisms on the Piton de la Fournaise volcanic cone. Courtesy of OVPDLF.

Radon. None of the six radon stations transmitted by radio showed significant changes during the seismic crisis; however, about 36 hours before the crisis, two of the stations, Chateau Fort and Cratere Catherine, recorded distinct Gaussian-like anomalies for a period of 15 hours. These changes were significantly above the background signal of 1-5 counts per hour (figure 39). Thus increased radon flux might have been a precursor to the intrusion.

Figure 39. Radon flux at stations Chateau Fort and Cratere Catherine at Piton de la Fournaise. Courtesy of OVPDLF.

Information Contacts: Thomas Staudacher (Email: staud@iremia.univ-reunion.fr), Patrick Bachèlery (Email: bachel@iremia.univ-reunion.fr), Valéry Ferrazzini (Email: ferraz@iremia.univ-reunion.fr), and Kei Aki (Email: aki@iremia.univ-reunion.fr), Observatoire Volcanologique du Piton de la Fournaise (OVPDLF), 14 RN3, le 27Km, 97418 La Plaine des Cafres, La Réunion, France.

02/1998 (BGVN 23:02) First eruption in over 5 years begins 9 March

Piton de la Fournaise began erupting 9 March at 1500 preceded by a number of earthquakes and strong deformations. The volcano had been quiet since the last fissure eruption on 27 August 1992. The Volcanological Observatory of Piton de la Fournaise (OVPDLF) was able to give authorities two days warning of the impending crisis. Thomas Staudacher, director of OVPDLF, deployed additional seismic and deformation monitoring equipment in the early stages of the event.

Eruptions first started from a fissure at 2,450 m on the N flank of the terminal Dolomieu crater, a spot in the interior of l'Enclos Fouqu' caldera (figure 40). Venting quickly migrated northward to lower altitudes (1,950 m). The activity was focused at two fissures near the very bottom of the slope of Dolomieu and cones were forming at the place where lava fountains were most active.

Figure 40. Sketch map of Piton de la Fournaise and vicinity. Notice that the topographic contour intervals are uneven. Courtesy of OVPDLF.

The lava fountains, some reaching 50 m in height, fed a voluminous flow that progressed N and E towards the Indian Ocean. Lava issued in a sustained flow rate estimated at 20 m3/s; the total volume since the start of the eruption was estimated on 10 March at 7 x 106 m3. The zone where the lava was flowing, to the NE along Osmondes plain in the direction of the sea, is wholly uninhabited. By 10 March activity appeared to be weakening, the front of the flow moving more slowly towards Grandes Pentes. Mist and haze over the Osmondes plain on 11 March prevented observation of the advance of the flow.

Seismicity had increased since the beginning of 1998. Volcanic tremor accompanied venting, including an almost continuous seismic swarm (30 earthquakes per hour in the hours preceding the eruption) beneath the summit's Bory crater in the SW. In the hour before magma venting, inclinometers in the summit area indicated the injection of a dyke and then the opening of a surface fissure. Tremors and swarm were accompanied by intermittent earthquakes, discrete events not usually seen in Piton's past eruptions.

By 1600 on 11 March, cones of scoria had attained heights of 10 m on Piton's upper slopes and 30 m on its lower slopes and were being fed by lava fountains nearly 30 m high. On 12 March at about 0245, a new but much less productive eruptive fissure opened on the opposite (SW) side of the terminal cone at 2,250 m elevation.

A "level one" volcano alert was issued 9 March at 0500 by island prefect Robert Pommies following heavy seismic activity during the weekend. The alert was reduced to "level two" after it was seen that the lava eruption was centered on the N of the volcano. Agence France Presse reported that there was no threat to the village of Sainte-Rose, which had to be evacuated in 1978.

A 14-16 March report stated that eruptive activity at both fissures (N and SW of the central cone) continued uninterrupted through 12 March. Emissions at the N fissures focused on the central vents and built cones ~50 m high. The output rate was ~15-30 m3/s and the lava flow front was stationary (4 km E at ~1,100 m elevation) with a maximum lava temperature of 1,167°C. Also, venting on the SW fissure centered on a limited stretch and built a spatter rampart ~70 m long. The output rate was ~5-10 m3/s with a maximum temperature of ~1,135°C. The latter activity gave rise to a 1.5 km flow. The discrete seismic events that were observed over the continuous tremor had ceased since 12 March but a single event was observed in the night of 13-14 March.

Information Contacts: Thomas Staudacher, Director, Observatoire Volcanologique du Piton de la Fournaise (OVPDLF), 14 RN3, le 27Km, 97418 La Plaine des Cafres, La Réunion, France (Email: Thomas.Staudacher@univ-reunion.fr, URL: http://www.ipgp.jussieu.fr); Agence France Presse, Paris, France.

03/1998 (BGVN 23:03) Geophysical portrayal of the March fissure eruptions

The following is a summary of observations from scientists at the Observatoire du Piton de la Fournaise and Observatoires Volcanologiques (OVPF), Institut de Physique du Globe de Paris, and the Laboratoire des Sciences de la Terre, Université de la Réunion.

Narrative. An eruption broke out on Piton de la Fournaise (PdF) at 1505 on 9 March 1998, after an unusually long period of 63 months rest. PdF (figure 41) had an average eruption rate of more than one per year in the last several decades. For a time three fissure vents were simultaneously active. The eruption continued at one fissure vent (Piton Kapor) at least as late as 20 April 1998.

Figure 41. Schematic map of Piton de la Fournaise showing the 9 and 11-12 March vents, newly named scoria cones and related features, and the extent of lava flows as of 15 March. Courtesy of Thomas Staudacher, OVPF.

Following escalating seismicity seen over the past two years, a seismic swarm developed at 0338 on 9 March (figures 42, 43, 44, and 45). The swarm was under the edifice, centered slightly W of the small Bory crater, a feature that lies immediately W of the larger Dolomieu crater. In the first observation of its kind at PdF, hypocenters progressed towards the surface prior to the eruption (figure 44).

Figure 42. The number of seismic events accumulated annually at Piton de la Fournaise during 1996, 1997, and early 1998 (three separate curves). The seismic swarm at the end of November 1996 was not followed by an eruption. A significant change in the earthquake rate started in July 1997 and accelerated in early 1998. Courtesy of OVPF.
Figure 43. Located earthquakes at Piton de la Fournaise from 1957 on 6 March through 1857 on 10 March (top) and a vertical, E-W cross section showing hypocenters from 0000 on 8 March through 1200 on 9 March (bottom). Coordinates (labeled tic marks) for horizontal distances on the map and cross section are 5 km apart; this scale differs from the vertical scale on the cross section. Courtesy of OVPF.
Figure 44. During the seismic crisis on PdF hypocenters migrated upward during the pre-eruptive 36-hour period shown (0000 on 6 March-1200 on 9 March). This was the first observation of its kind at PdF; pre-eruptive seismicity had usually remained diffusely distributed within the whole edifice. Courtesy of Jean Battaglia and Nelly Rousseau, OVPF.
Figure 45. Pre-eruptive earthquake counts at Piton de la Fournaise and seismic moments for 8-9 March 1998 (times are GMT). Noteworthy points are labeled as follows: at A, focal depths of the volcano-tectonic events started at ~5 km below sea-level; at B they reached 3 km; at C, 2 km; and at D, 1 km. At E, there occurred the first long-period (near 1 Hz) event since 1993. Venting started at 1505 (1105 GMT). Courtesy of OVPF.

The summit deformed rapidly beginning around 1400. An example of clear and sudden inflation appears in figure 46, documenting changes in radial and tangential inflation at station "Bory." Another multi-component station ("Soufriere"; immediately N of Dolomieu crater) underwent similarly rapid, though larger amplitude, displacement beginning at 1410 and peaking at 1424 to 1429 (undergoing up to 200 µrad of tilt). Inflation at Soufriere station indicated migration of magma towards the N eruptive fissures. Surface venting started there at 1505.

Figure 46. Ground deformation at the summit of Piton de la Fournaise on 9 March during 1200-1700 (0800-1300 GMT). Surface venting began at 1505 (1105 GMT). The Bory two-component inclinometer, ~200 m S of Bory crater, measures tilt aligned radial and tangential to the volcano. The rapid inflation at 1011 GMT was linked to near-surface dike emplacement. Contact the authors for collateral inclinometer and extensometer data at other summit stations. Courtesy of OVPF.

EDM and GPS measurements showed concordant displacements at points around the summit (figures 47 and 48). The time-sequence of EDM data indicated that essentially all deformation occurred at the time of eruption. Consistent with the deformation, eruptive fissures developed between the reflectors to the NE and NW of the summit.

Figure 47. Automated electronic distance meter (EDM) measurements at Piton de la Fournaise taken from an instrument on the NW rim of the Enclos Fouqué caldera (star, labeled 1B10). The EDM computed distances and azimuths to 13 reflectors (triangles) on the flanks of the terminal cone. The numbers indicate centimeters of total displacement between 1000 and 1400 GMT on 9 March. Weather permitting, these measurements were made every hour and telemetered to the observatory in near real-time. Only reflectors E of the fissures underwent measurable relative motion, moving E up to 34 cm. Courtesy of OVPF.
Figure 48. GPS measurements at Piton de la Fournaise showing horizontal displacements in centimeters from GPS positioning in November 1997 and 15 March 1998. Courtesy of OVPF.

At 1505 on 9 March tilt on the northern summit inclinometer reversed and seismic tremor commenced, indicating the final stages of dyke emplacement and the onset of venting. Although at the time, bad weather impaired visual observation, venting was recognized, starting on a 150-m-long N-S fissure around 2,450 m elevation on the N flank of the terminal cone (figure 41). The fissure system quickly developed in an en echelon pattern stretching downslope to approximately 2,100 m elevation. Major venting migrated to the fissure's lower stretches where lava fountaining up to 50 m high fed a flow that descended E (towards an area of the N caldera called the Plaine des Osmondes). Vigorous venting continued through the night of 9 March.

A few discrete seismic events were observed through the tremor during the next two days (10-11 March). The approximate locations of the events were SW of Bory crater. During 10-11 March venting continued in the N along two 100-m-long fissures. At the time, scientists lacked visual observations of the flow front due to cloud cover. Earthquakes at Piton de la Fournaise generally cease after an eruption has broken out, but in this case they continued, hence the impending opening of a new eruption fissure was forecast for the next few hours or days.

In accord with this forecast, during the night of 11 March until 0245 the next morning, a new, isolated eruptive fissure opened WSW of the Bory crater. The vent established itself S of the other erupting fissures, at ~2,200 m elevation (figure 41). Although lava escaped at a much lower rate here than along the northern vents, this southern fissure emitted lava along a zone ~100 m in length. Fountaining lava reached ~10 m high and fed a flow that by 0800 on 11 March had traveled 200-300 m downslope.

During the following days, eruptions continued at both the two northern fissures as well as the southern fissure. Estimated emission rates on the N were 30-50 m3/s and on the S at 5-10 m3/s. Issuing from the northern fissures, E-traveling lava descended to ~1,100 m elevation by 15 March. Here, ~4 km away from the vents, the flow front became stationary. Around the same time, lava issuing at the southern fissure reached an estimated length of 1,500 m. Maximum lava temperatures reached 1,167°C at the northern vents and 1,157°C at the southern vent.

Venting was progressively restricted to limited stretches of the three fissures where scoria cones started to grow. By 19 March the scoria cones were ~40 m high and 120 m long at the upper-elevation northern site, ~35 m high at the lower-elevation northern site, and 15 m high at the southwestern site.

Features at these cones were designated as the Maurice and Katia Krafft crater, Piton Kapor, and the Fred Hudson crater (figure 41). Activity at the three cones continued, but progressively decreased until venting was restricted to Piton Kapor by 31 March. Piton Kapor was still quite active as of 20 April 1998.

Preliminary petrography indicated that the lavas were mostly aphyric basalts carrying a small but variable number of millimeter-sized olivine crystals. Under the assumption that their composition lay close to the so-called "stationary basalts," modeling indicated that they vented at temperatures close to their liquidus.

Premonitory geophysical observations. Clear-cut long-term observations on the various surveillance networks that signaled an impending eruption were, as is customary at PdF, discrete and few. Increasing seismicity late in 1997 and accelerating in early 1998 were signs that an abnormal situation was developing. However, other crises, albeit of smaller intensities, occurred in November 1996 and July 1997 and did not result in an eruption. Small perturbations were seen on the deformation (inclinometry, geodesy, and extensometry) networks months before the present event but were not interpreted as premonitory. These signs most probably corresponded to magma intrusions within the edifice.

Surveillance network observations. It was only a few hours before the 9 March outbreak that short-term signs definitely signaled an impending eruption and civil authorities were warned of a maximum alert. Critical signs included seismic, tilt, and deformation data (summarized on figures 42 to 48). In addition, a total-field magnetometer network provided clear pre- and syn-eruptive signals that remain under interpretation. Measurements on about 50 of the approximately 100 microgravity-benchmark and GPS-array stations were repeated between 18 and 31 March with two Scintrex CG-3M gravimeters. The array was last surveyed in December 1997. A few stations showed variations of relatively small amplitude. Interpretations must await correction of the elevation changes and comparison with the recordings provided by the two permanent monitoring stations installed in December 1997. Radon stations did not show any unusual pattern either before or during the first stages of the outbreak as was hoped from previous behavior during intrusive events (BGVN 21:12).

The Observatoire Volcanologique du Piton de la Fournaise(OVPF) was built in 1979 after the devastation of the 1977 eruption owing to the financial help of the Institut National des Siences de l'Univers, France. The Observatory became operational in 1980; since then, tens of eruption have been closely observed and, most often, forecast sufficiently in advance to alleviate possible personal and material damages.

Besides the information contacts listed below, report contributors also included Kei Aki, Valérie Ferazzini, Louis-Philippe Ricard, Nelly Rousseau, Jean Battaglia, Nicolas Villeneuve, Philippe Kowalski, Philippe Catherine, Denis Wégerlé, Grégory Durand, Nadia Talibart, Jacques Lebreton, Maolidi Assoumani, Massimo Bonfiglio, Bernard Robineau, Jean-Lambert Join, Eric Delcher, Jean-Luc Folio, Jean-Luc Hoareau, Cécile Savin, Hamidou Nassor, Evelyn Maillot, Jean-Claude Lépine, Martine Hirn-Sapin, Christine Deplus, Pierre Briole, Sylvain Bonvalot, Jacques Zlotnicki, Germinal Gabalda, Philippe Labazuy, Alfred Hirn, Jean-Claude Delmond, Guy Aubert, Michel Diament, and Janine Gouin.

Information Contacts: Thomas Staudacher, Observatoire Volcanologique du Piton de la Fournaise (OVPF), 14 RN3, le 27Km, 97418 La Plaine des Cafres, La Réunion, France (Email: staud@univ-reunion.fr); Patrick Bachèlery, Département des Sciences de la Terre, Université de la Réunion, BP 7151, 15 Avenue Rene Cassin, 97715 Saint Denis Cedex 9, La Réunion, France (Email: bachel@univ-reunion.fr); Michel P. Semet and Jean-Louis Cheminée, Observatoires Volcanologiques, Institut de Physique du Globe de Paris, 4 Place Jussieu, 75252 Paris Cedex 05, France (Email: semet@ipgp.jussieu.fr, cheminee@ipgp.jussieu.fr, URL: http://www. ipgp.jussieu.fr).

06/1998 (BGVN 23:06) April-June lava flows on Plaines des Osmondes and beyond

Crater activity was vigorous and variable during late April. It included lava fountains and gas-piston events. After that, and as late as mid-July, observers saw only occasional projections of lava.

The first lava flows emerging into the Plaine des Osmondes blocked the outflow of subsequent lavas from Piton Kapor (see maps, BGVN 23:02 and 23:03). Later flows went N and followed the caldera wall E towards the Plaine des Osmondes, often traveling through lava tubes. Overflow and accumulation of basalt around Piton Kapor formed three distinct, nearly horizontal plateaus several hundred meters across and up to 40-50 m thick. Magne crater, formed in 1972 only 400 m below Piton Kapor has almost disappeared beneath the new lava flows. The emitted volume was estimated at 40-50 x 106 m3, which would mark this eruption as one of the most voluminous during this century. Piton Kapor is the largest and most noteworthy cone within the caldera.

Lava flows overran the Plaine des Osmondes on 6 July. The overflow went down to Grandes Pentes, burning some vegetation, bushes, and trees. Its maximum length reached ~10 km. The front of the flow was at ~350 m altitude, only 2 km from the national road. No further advance of the front has been observed.

Tremor decreased through April until mid-May and then remained constant until 10 July. During 10-18 July tremor increased and was more unstable, probably due to collapse of lava tubes. Normal levels of tremor resumed in late July.

Information Contact: Thomas Staudacher, Observatoire Volcanologique du Piton de la Fournaise (OVPF), 14 RN3, le 27Km, 97418 La Plaine des Cafres, La Réunion, France (Email: staud@univ-reunion.fr).

07/1998 (BGVN 23:07) New lava flow traverses 12 km across the E flank

The eruption that began in March (BGVN 23:03) continued in August. A new lava flow crossed the Plaine des Osmondes and went down the E flank towards the sea. As of 31 July its front had reached 250 m from the new national road. By 3 August it had slowly progressed to within 100 m of the road. On 4 August the front moved forward suddenly; within a few hours it had crossed the old national road and stopped ~3 m in front of the new national road. No new movement of the lava flow was observed during the next week. The flow had reached a total length of 12 km. Some small but new lava flows were visible in the upper part of the Grand Brûlé. Tremor episodes had diminished in the past few months, but beginning on 6 August there was a sudden tenfold increase over levels of the preceding weeks. The increased activity persisted the following week.

Information Contacts: Thomas Staudacher, Observatoire Volcanologique du Piton de la Fournaise (OVPF), 14 RN3, le 27Km, 97418 La Plaine des Cafres, La Réunion, France (Email: staud@univ-reunion.fr).

09/1998 (BGVN 23:09) Activity ends with fissure eruptions outside the caldera

The eruption that began in March (BGVN 23:03) diminished during August and September. Observatoire Volcanologique du Piton de la Fournaise (OVPF) considers the eruption ended. The most significant activity during the last two months took place outside the caldera.

A small fissure eruption began on 9 August north of the caldera. Lava issued from this fissure, which was located ~500 m from the caldera wall near Nez Coupé Sainte Rose (figure 49). The initial eruption lasted only 24 hours, but a second fissure eruption began 14 August in the same area closer to the caldera wall. No fountains were observed with the second fissure, although the lava was very fluid. Flows eventually measured 200-300 m wide and ~2 km long. They moved parallel to the caldera wall until 14 September when they stopped ~500 m above Trou Caron. Some of the lava reached the edge of the caldera and spilled over onto the Plaine des Osmondes through three separate rivulets. A flow that was moving towards the upper part of Bois Blanc (a village located on the east coast) stopped by 25 August.

Figure 49. Map of the NE quadrant of Piton de la Fournaise showing important craters and other features. The dark tone represents the caldera wall, the light-gray areas indicate the extent of lava flows dating from 1972. The medium-gray shows flows since March 1998. Courtesy of OVPF.

During September, some night incandescence due to the lava lake at Piton Kapor was seen. Only weak tremor was observed. Beginning 5 September some gas-piston events were recorded; these had likely taken place before, but had remained undetected during stronger episodes of tremor.

This eruption, including all tremor and degassing at Piton Kapor, ended 21 September, after 196 days of activity. It thus comprised the volcano's longest and one of it's most voluminous eruptions of this century.

Information Contact: Thomas Staudacher, Observatoire Volcanologique du Piton de la Fournaise (OVPF), 14 RN3, le 27Km, 97418 La Plaine des Cafres, La Réunion, France (Email: staud@univ-reunion.fr).

07/1999 (BGVN 24:07) A fissure eruption begins 19 July

A new eruption on 19 July was preceded by ten days of seismic activity. On 14 July, there was an earthquake of magnitude 2.3, but otherwise activity was low (3.5 events per day). At 1817 on 19 July, there was a seismic swarm of 77 earthquakes measuring under M 1.0 and one measuring M 1.2; later, at 1856, tremors began being registered at the summit seismic stations. Earthquake epicenters were at Dolomieu crater; focal depths were between slightly above sea level and the ground surface. In the evening lava fountains of up to 100 m height could be observed from the national highway in the "Grand Brûlé."

Weather conditions did not permit field observations until 21 July, when a 500-m-long fissure with small cones was discovered trending N to W across Dolomieu crater and beyond it to the ESE. On Dolomieu crater's W margin a larger cone straddled the crater's border. About 25% of the Dolomieu surface was covered by the new lava field. On 21 July, volcanic activity inside Dolomieu was limited to degassing on the E side of the new crater. Only steaming could be observed on the E flank and bad weather subsequently closed in.

On 23 July seismicity increased for 11 hours. Again, weather conditions did not allow field observations for another two days. Then, during a helicopter flight on 25 July, observers saw two lava fields. The first contained aa lava on the N of the crater (100 m across, 1.5 km long, and 1-2 m thick). The second contained pahoehoe lava on the E of the crater; these were still active, with dozens of small (under 1 m thick) flows. The first lava field was probably emplaced during the 19 July eruption and the second during the eruption on the night of 23 July. As of 26 July tremor and eruptions continued.

A basaltic shield volcano, Piton de la Fournaise forms the SE half of Réunion Island, 700 km E of Madagascar. It has been one of the most active oceanic volcanoes, with more than 100 eruptions in the last 300 years. Three calderas formed at around 250,000, 65,000, and <5,000 years ago by progressive eastward slumping of the volcano. Most historical eruptions originated from the summit and flanks of a 400-m-high lava shield within the youngest caldera.

Information Contacts: Thomas Staudacher and Jean Louis Cheminée, Observatoire Volcanologique du Piton de la Fournaise (OVPF), 14 RN3, le 27Km, 97418 La Plaine des Cafres, La Réunion, France (Email: staud@univ-reunion.fr).

09/1999 (BGVN 24:09) September-October eruption generates lava fountains and flows

Less than 2 months after the end of the eruption of July (BGVN 24:09), a new seismic crisis started at 1037 on 28 September. Most of the observed 189 seismic events had magnitudes of less than 1. All were situated above sea level. Only two of them had significantly larger magnitudes of 1.8 and 2.2, at 1042 and 1053, respectively.

An eruption started at 1158 in the W part of Dolomieu crater with a strong whistling noise. Seconds later, a 10-m-diameter, ~50-m-high lava fountain rose from the SW corner of Dolomieu crater. Immediately after that, a fissure formed going NW, followed by the development of small lava fountains and a lava flow. Less than 5 minutes later the fissure measured ~200 m long and was terminated by another lava fountain 20-30 m high. At 1210, the fissure opened on the S flank "en echelon," ~100 m below the crater rim. The two upper fissures measured ~50 m long, followed by a third one ~250 m. The lava flow down the steep S flank extended ~1 km in less than 15 minutes. It continued to the SE on a more gentle slope and reached "Château Fort" crater, 2 km away, within two hours.

Less than 8 hours after the eruption started, activity was limited to some individual points on the upper S flank, while the main lava flow had stagnated. No further activity was observed in the Dolomieu crater. In the night, small fissures on the S flank at 2,150 m elevation produced some small pahoehoe lava flows.

On 8 October, after a significant increase of tremor, steam release was observed in the south "enclos," at 1,900 m altitude, ~4 km away from Dolomieu crater and on the morning of 11 October a new 600-m-long lava flow was observed 500 m to the SE, on the base of crater "Villèlle," close to southern border of the caldera. On 18 October this lava flow measured ~1.5 km. No further activity was observed at this site on 21 October. As of 22 October tremor was still visible, mainly in form of small "gas piston events," centered on the upper fissures on the S flank of Fournaise, where a small cone was formed. The eruption ended following small "gas piston events" on at about 1800 on 23 October. Residual fumarolic plumes, consisting primarily of water vapor, were visible the following week.

Mapping of the lava flow was performed in the first days by use of small hand-held GPS. Early lava flows, in Dolomieu crater and on the S flank are mainly aa lava flows. In the Dolomieu crater, it represents a surface of ~40,000 m2 (?) and a volume of <100,000 m3. It partly covered the July lava flow. On the border of the lava flow we could observe fissuring of the ground, up to 3 m deep, due to the weight of the new up to 3-m-high lava flow.

The main lava flow on the S flank represents about 300,000 m2 and <1 x 106 m3. Taking into account an emplacement within less than 5 hours, the eruption rate was estimated to be >50 m3/s. The small pahoehoe flow from the fissures at 2,150 m altitude covered less than 5,000 m2.

The southern-most lava flow starting at crater Villèlle also was mainly pahoehoe. There were no projections at its point of emission, indicating a highly degassed magma. On 11 October a ~1 m lava flow emerged from a small "well" on the SW base of "Villèlle." The volume of this lava flow is estimated to be under 50,000 m3. All recovered samples were aphyric basalt.

Information Contacts: Thomas Staudacher, Nicolas Villeneuve, and Jean Louis Cheminée, Observatoire Volcanologique du Piton de la Fournaise, Institut de Physique du Globe de Paris, Institut National des Sciences de l'Univers, 14 RN3 - Km 27, 97418 La Plaine des Cafres, Réunion, France (Email: staud@ipgp.jussieu.fr, URL: http://volcano.ipgp.jussieu.fr:8080/reunion/stationreu2.html).

01/2000 (BGVN 25:01) A new eruption in February 2000 begins venting lava flows

A new eruption occurred at Piton de la Fournaise in February 2000. The previous eruption, in September and October 1999 (BGVN 24:09), included a ~50-m-high lava fountain rising from the SW corner of Dolomieu crater and a main lava flow covering ~300,000 m2 on the S flank in a deposit with a volume of <1 x 106 m3.

Following a significant increase of seismicity during January 2000, a seismic crisis started at 2335 on 13 February and the eruption began at 0018 on 14 February. At least five vents opened "en echelon" on the N flank. These vents formed two N-flowing lava fields. One, consisting of aa lavas, formed on the E side of crater "Puy Mi-Cote", and the second issued from a large fissure above "Piton Kapor" (BGVN 23:03). Both flows joined close to the border of the caldera and followed the slope eastward to "La Plaine des Osmondes." At about1100 on 14 February, lava fountains on the main fissure were 5 m high. Further observations were hampered by very heavy rainfall and winds from a tropical storm centered 250 km N of Réunion Island.

Information Contacts: Thomas Staudacher, Nicolas Villeneuve, and Jean Louis Cheminée, Observatoire Volcanologique du Piton de la Fournaise, Institut de Physique du Globe de Paris, Institut National des Sciences de l'Univers, 14 RN3 - Km 27, 97418 La Plaine des Cafres, Réunion, France (Email: staud@ipgp.jussieu.fr, URL: http://volcano.ipgp.jussieu.fr:8080/reunion/stationreu2.html).

07/2000 (BGVN 25:07) Eruptions in February, March, June, and July 2000

During 14 February to 4 March 2000 an eruption occurred at Piton de la Fournaise that was briefly mentioned in a previous report (BGVN 25:01) and is discussed here in more detail. After 4 March through May, there was no volcanic activity and seismicity was low with 1-2 events per month. On 23 June volcanism recommenced with an eruption that lasted more than a month.

Eruption of 14 February 2000. Three and a half months after its previous eruption (BGVN 24:09), Piton de la Fournaise erupted on 14 February. Throughout January, seismicity was well above normal levels until the beginning of February when a relative lull in seismicity lasted for two weeks (figure 50). At 2314 on 13 February a seismic crisis began that lasted 64 minutes. A total of 261 earthquakes occurred with magnitudes up to 1.9. The deepest events were localized at sea level, just below Dolomieu summit crater (figure 51).

Figure 50. Seismic events at Piton de la Fournaise during December 1999- February 2000 shown as a series of five day averages. Heightened activity occurred through January, and a relative lull in activity occurred two weeks prior to the eruption on 14 February. Seismic information was not available for the beginning of the eruption (February 14-24). Courtesy of OVPDLF.
Figure 51. Map of the N flank of Piton de la Fournaise showing the lava flows from the 14 February 2000 eruption (black), fissure vents (white lines within the flow), and the major features associated with the flow. Note Dolomieu summit crater at lower edge of the map. Courtesy of OVPDLF.

On 13 February, three minutes after the beginning of the seismic crisis, the first significant variations in deformation were recorded at 2317 and 2320, on radial and tangential components, respectively, by the "Dolomieu Sud" tiltmeter station. After initial deformation was observed, tiltmeter and extensometer stations at "Soufriere," "Bory," "Tunnel Catherine," and "Flanc Est" (figure 52) registered variations, with up to 270 µrad recorded for the "Soufriere tiltmeter" radial component. The intrusion of magma caused inflation under the summit crater. The inflation center started S of Dolomieu summit crater, migrated below Dolomieu, and then traveled to the N flank of the volcano where several vents opened (figure 53). At 0018 on 14 February, tremors registered at all of the seismic stations marking the beginning of the eruption.

Figure 52. Map showing the location of radon, deformation, magnetic, and seismic stations on Piton de la Fournaise in February 2000. Courtesy of OVPDLF.
Figure 53. During the 14 February 2000 eruption at Piton de la Fournaise the center of inflation migrated. The incenter of inflation was calculated on 5-minute intervals and plotted on this sketch map. The center of inflation was estimted based on the shift of deformation vectors over time. Courtesy of OVPDLF.

Inclement weather produced by cylone Eline passing 200 km N of Reunion inhibited visual observations for several days. After that, scientists found that several en echelon fissures were localized on the N flank starting at 2,490 m elevation (white lines within black lava flows, figure 53). An aa flow inundated the "Puy Mi-Côte" crater, passed to the W and E of the crater, and continued in the direction of "Piton Partage." Both vents were inactive at the time of observation. Eruptive activity was concentrated on a vent 300 m E of Puy Mi-Côte, where stable 20- to 30-m-high fountains were observed from a new crater, whose rim grew to 20 m high at that time. A second, much smaller crater was active about 100 m above the main crater. A large aa lava flow and meter-sized blocks descended in the direction of "Piton Kapor" (site of the 1998 eruption), then joined the first lava flow and followed the "rempart Fouqué" to the E. This lava flow terminated about 4 km away at 1,950 m altitude near "Nez Coupé de Saint Rose." Beginning on 24 February a large number of small pahoehoe lava flows were observed. For several hours on 4 March a large number of gas-piston events were observed and then at 1800 tremor stopped, marking the end of the eruption.

Retrospective analysis revealed that the initial aa lava flow represented most of the erupted material. The lava was particularly irregular with scoria that ranged in size from tens of centimeters to meter-sized blocks. Pahoehoe flows from the 24 February phase of the eruption partly covered the aa lava that was emitted earlier. The entire lava flow covered an area of about 1.3 x 106 m2 and comprised a total volume of about 4 x 106 m3 of aphyric basalt. The main new crater was called "Piton Célimène" (figure 53).

Eruption of 23 June 2000. Beginning in June, long-term deformation was observed at several stations near the volcano. Since the beginning of the month up to 0.1 mm of inflation took place at the "Soufrière" extensometer (figure 52). Starting on 12 June clear inflation of up to 70 µrad was observed at the "Dolomieu Sud" tiltmeter. After 20 June inflation of up to 20 µrad was observed at the "Château Fort" tiltmeter. The Château Fort extensometer showed variations in opening, shear, and vertical movement components.

Seismicity increased during 9-14 June with twelve deep earthquakes ~6 km below the W flank. During 15-21 June seismicity drastically increased with 2, 2, 4, 10, 29, 69, and 101 earthquakes recorded on successive days (figure 54). All of these earthquakes occurred below Dolomieu summit crater, with focal depths between sea level and 1 km above sea level. They had magnitudes up to 1.8 that increased with the number of earthquakes recorded. During the same time period, five deep earthquakes also occurred.

Figure 54. The number of daily seismic events recorded at two seismic stations at Piton de la Fournaise during 1 June through 6 July 2000. Courtesy of OVPDLF.

During 0600-0640 on 22 June, following 50 seismic events, there was a small seismic crisis that consisted of 36 low-energy seismic events. For 36 hours after the seismic crisis only very low-energy earthquakes occurred. At 1650 on 23 June another seismic crisis took place (figure 54). It consisted of about 300 earthquakes, including some greater than M 2 and possibly as high as M 2.5. Some of the earthquakes were recorded at the seismic station in Cilaos, more than 30 km from the volcano.

During the seismic crisis one shallow earthquake was centered under the E flank of the volcano. Around this time the observatory's tiltmeter network showed uplift of the central part of the volcano to over 200 µrad. The inferred effect of an intrusion was first localized under the summit region, then shifted to the SE. At 1800 eruption tremor began, and tremor localization suggested the eruption site was on the SE flank between "Signal de l' Enclose" and "Château Fort" craters between 1.9 and 2.2 km elevation. Figure 55 shows these named locations and the actual fissure vent and extent of lava flows.

Figure 55. Map and image composite of the 23 June 2000 lava flows on the E flank of Piton de la Fournaise. Courtesy of OVPDLF.

According to the observatory staff, the 23 June eruption began with the formation of a short-lived, 500-m-long, SE-trending fissure on the SE flank at an elevation of ~2,100 m (figure 55). A second, 200-m-long, ESE trending vent also formed on the SE flank at ~1,800 m. About eight lava fountains initially rose up to 50 m above the second vent. In addition, a 300-m-long aa lava flow traveled down the "Grandes Pentes" to an elevation of 580 m. About two days after the eruption began, the intensity of the lava fountains decreased, and the crater rim reached a height of 10-15 m.

Within 24 hours after the onset of the eruption, tremor rapidly decreased to less than 10% of the initial value. Unlike typical eruptions at Piton de la Fournaise, seismicity under the central crater continued for the first five days of the eruption. During 24-28 June there were 26, 22, 17, 17 and six seismic events, respectively, up to M 2.5. Similar seismic events occurred during eruptions in 1986, 1988, and 1998; in two cases they preceded the formation of new vents. However, no new vents formed during 24-28 June. After 29 June no seismic events were recorded, and starting on 27 June there was an increase in tremors that remained around initial levels and lasted three weeks. Throughout most of the eruption there was a lava lake in the eruption crater and several meter-sized lava flows emerged at its base reaching up to 300-400 m below the crater. Lava samples were collected during the eruption, and a lava temperature of 1,160°C was measured several times using a thermocouple.

On 30 July the eruption stopped after 37 days of activity. The initial flow was entirely aa lava, while the later outspreading lava flows were aa and pahoehoe lava. The entire lava flow covered an area of ~3 x 102 m2 and comprised a total volume of ~1 x 107 m3. The final crater was 26 m high and was named "Piton Pârvédi."

Information Contacts: Thomas Staudacher, Nicolas Villeneuve, Jean Louis Cheminée, Kei Aki, Jean Battaglia, Philippe Catherine, Valérie Ferrazzini, and Philippe Kowalski, Observatoire Volcanologique du Piton de la Fournaise, Institut de Physique du Globe de Paris, Institut National des Sciences de l'Univers, 14 RN3 - Km 27, 97418 La Plaine des Cafres, Réunion, France (Email: staud@ipgp.jussieu.fr, URL: http://volcano.ipgp.jussieu.fr:8080/reunion/stationreu2.html).

12/2000 (BGVN 25:12) 12 October-13 November eruption near July eruption site

Piton de la Fournaise erupted several times during 2000; 14 February to 4 March (BGVN 25:01), 23 June to 30 July (BGVN 25:07), and in October. The last eruption in 2000 began on 12 October after two periods of inflation, high pre-eruptive radon emissions, and three weeks of increased seismicity beneath the volcano.

During the two months prior to the eruption, two tiltmeter stations, "Dolomieu Sud," located at the volcano's summit and "Château Fort" on its southern base, showed tilt variations of up to 50 µrad, which indicated a clear inflation of the S flank. In addition, extensometer data at Château Fort showed that fissure openings had significantly increased since the preceding eruption in June 2000. The fissure expansions confirmed that inflation was occurring.

Three weeks prior to the eruption high seismicity occurred under the volcano, with 10 to 20 earthquakes per day. A small seismic crises that consisted of 57 earthquakes occurred on 6 October (figure 56). Thereafter, the number of seismic events returned to the high levels that had been recorded during the previous 3 weeks until the number of earthquakes significantly increased on 12 October, marking the beginning of the eruption. All of the 278 seismic events that occurred between the end of September and 12 October were of very low energy, usually with magnitudes less than 0.7. Only seven earthquakes were recorded with higher magnitudes, ranging between 0.9 and 1.7.

Figure 56. The number of daily seismic events recorded at seismic stations at Piton de la Fournaise during 10 September through 21 October 2000. Courtesy of OVPDLF.

In addition to increased seismicity, high radon activity was measured at the volcano. Three different probes in soil and old eruption vents at the "Bory" station on the W rim of the summit crater showed a high mean level of radon activity. The "Bory 3" radon probe showed about 40 counts per day, which was 2.7 times higher than during January-May 2000. OVPDLF scientists determined that the high counting rates indicated a general increase in volcanic gas emissions from the volcano, reflecting the presence of degassing magma.

At 0401 on 12 October a seismic crisis began that consisted of 201 low-energy events (figure 56). All but five events had magnitudes less than or equal to 1.1, with the largest being 1.6. The seismic crisis lasted 64 minutes and at 0505 a strong eruption tremor, which was localized on the E flank of the volcano, appeared at the summit stations. Visual observations helped to constrain the eruption site between "Signal de l'Enclos" and "Le Langlois" craters, and above "Piton Pârvédi" crater, which formed during the previous eruption in June 2000 (figure 57). Field observations conducted with a hand-held GPS receiver allowed scientists to precisely locate the two fissures where lava was emitted during the eruption. The smaller fissure (fissure 1) was several tens of meters long, located at 2,260 m in altitude, and emitted a small, 50-100 m long aa lava flow. The other fissure (fissure 2) was 680 m long and ran continuously between 2,220 m and 2,000 m in altitude.

Figure 57. Sketch map showing the location of craters of the 12 October activity and fissures where lava flows were emitted. PDN (Piton de Neiges) is a coordinate system used on Reunion Island by IGN and other scientists. In general, IGN maps include both PDN and international ellipsoid coordinates. Courtesy of OVPDLF.

Almost all of the lava-flow activity occurred at fissure 2. At 1100 on 12 October, lava fountaining still occurred within the lower 350 m of fissure 2, and lava output was relatively high. A large network of numerous aa lava flows of up to 200 m width traveled down the SE flank of the volcano towards "Piton Pârvédi" and continued in a single, large lava flow for 5.5 km on the southern border of the June lava flow until reaching 400 m in altitude. At 2100 on 13 October, about 40 hours after the eruption began, the rate of lava emission was still high with an estimated rate of 40-60 m3/s. A continuous incandescent lava flow, at least 2 km long, was visible.

The following day volcanic activity was focused on the lower end of fissure 2, and a crater began to build up. It was named "Piton Morgabim." Initially the crater was U-shaped with an opening towards the ESE. Throughout the entire period of activity a permanent lava lake was present within the crater, and lava flows were observed on the downhill (SE) side of the crater. During the first week of November the crater closed so that the lava lake was no longer visible, and the upper crater walls were high and sub-vertical. Several tunnels began to form and a tumulus that was several tens of meters high piled up in front of "Piton Morgabim" (figure 58). Since the end of October pahoehoe lava flows appeared in the upper part of the initial aa lava flows and surrounded "Piton Pârvédi" crater to the N and S.

Figure 58. Photograph of the eruption, taken from the SW at 0943 on 9 November from a helicopter. The photograph shows the initial crater ("Piton Morgabim") and the new vent (circled to the left) and an active incandescent lava flow channel. The pahoehoe lava flows above "Piton Pârvédi" that began in late October can be distinguished (gray area), as well as the tumulus in front of "Piton Morgabim." Courtesy of OVPDLF.

Since 29 October, tremor began to increase until it reached the same high value as during the first minutes of the eruption. Tremor remained at high levels for the following 5 days. Beginning on 5 November strong degassing and liberation of H2S occurred just above "Piton Morgabim." On 8 November the upper crater walls collapsed and the [lava] lake, which was ~40 m in diameter, was visible again. On 9 November an intense explosion occurred ~50 m NW of "Piton Morgabim" crater, and rocks and lava were ejected up to 200 m in altitude. A second vent formed in this area and both it and "Piton Morgabim" were simultaneously active for several tens of hours (figure 58 and 59). From 12 November, explosions and black ash were observed at the upper vent, which were most likely phreatomagmatic features. Lava bombs were ejected up to 250 m away from the vent. Both vents fused together, and the initial crater raised up, finally forming one single large crater named "Piton Morgabim" (figure 59). Figures 16 and 17 show different stages of the vents growing together. During the period of increased tremor, new several-km-long pahoehoe flows formed. Again they surrounded Piton Pârvédi to the N and S and covered large parts of the June 2000 lava flow. In particular, one pahoehoe lava flow extended beyond the front of the June eruption in the "Grand Brûlé" by ~500 m length down to 370 m elevation.

Figure 59. Photograph of "Piton Morgabim" and a second crater coalescing at Piton de la Fournaise. The photograph was taken on 11 November from the E flank of the volcano. The saddle-shaped separation between the two craters disappeared during the next days. Bright spots to the left and right of the craters were emanations from the lava flow and fissure 2, respectively. Courtesy of P. Morin.

The high level of tremor suddenly disappeared at 2310 on 13 November, marking the end of the eruption. By this time the remaining crater, "Piton Morgabim," was ~100 x 75 m across and 30-40 m deep (figure 60). On 15 November, the lava flow SE of the crater was still hot; a temperature of ~800°C was measured 40 cm below the surface.

Figure 60. Photograph of the surface of the affected area of Piton de la Fournaise after the eruption. The black line shows the outline of the lava flow. Courtesy of OVPDLF.

Basalt samples were collected throughout the eruption. The initial basalt was apheric, near the end of October olivine crystals appeared, and near the end of the eruption the basalt had numerous centimeter-sized olivine crystals.

Digital photos were analyzed in order to map the lava flow and to obtain an estimate of it's erupted volume. The total erupted volume was estimated to be on the order of 5 x 106 m3, which is a typical value for eruptions at Piton de la Fournaise.

Correction. In BGVN 25:07 the area of the entire lava flow from the 23 June-30 July 2000 eruption of Piton de la Fournaise was reported as being 3 x 102 m2, when it was actually 3 x 106 m2.

Information Contacts: Thomas Staudacher, Jean Louis Cheminée, Observatoire Volcanologique du Piton de la Fournaise, Institut de Physique du Globe de Paris, Institut National des Sciences de l'Univers, 14 RN3 - Km 27, 97418 La Plaine des Cafres, Réunion, France (Email: staud@univ-reunion.fr, URL: http://volcano.ipgp.jussieu.fr:8080/reunion/stationreu2.html).

05/2001 (BGVN 26:05) Eruptions during late March 2001 and on 11 June 2001

In 1998, after 5.5 years of calm, Piton de la Fournaise erupted twice. Two eruptions occurred in 1999, while in 2000, three eruptions took place (BGVN 25:12). Only 4.5 months after the last eruption in October 2000, Piton de la Fournaise erupted once more on 27 March 2001 at 1320. As described below, precursor extensometer and tiltmeter measurements, in conjunction with historical data, provided an accurate forecast of an eruption sometime near the end of March. The March eruption was followed by another at 1350 on 11 June.

Geodetic measurements. After 1 January 2001, the Château Fort extensometer showed a significant, regular increase (figure 61), and, beginning 21 January, the Magne extensometer showed the same tendency. Plots of the measurements from these two stations show remarkably constant slopes of 0.0038 mm/day at Château Fort and 0.005 mm/day at Magne. In 1999 and 2000, such variations were observed 2-3 months before the eruptions of 19 July 1999, 23 June 2000, and 23 October 2000 on the E and SE flanks of the volcano. Using these historical data and the fact that the maximal variation of spread for all these eruptions was 0.25 to 0.35 mm for the Château Fort station and 0.3 to 0.5 mm for the Magne station, extrapolations of the deformation were used to forecast a late March eruption.

Figure 61. Extensometer measurements from the Château Fort station at Piton de la Fournaise during mid-December 2000-early April 2001. Courtesy of T. Staudacher, OVPF.

Almost simultaneous with the extensometer-measured tilt increases, important variations were registered by the Dolomieu Sud and La Soufrière tiltmeters. The Dolomieu Sud radial tiltmeter measurements increased considerably after 6 January 2001 compared to those for the previous two years; similar variations were observed before the 12 October 2000 and 28 September 1999 eruptions (figure 62). The measured increase of ~110 µrad of radial tilt as observed at Dolomieu Sud between January and March 2001 could not be explained by temperature changes. Rather, it indicated a significant inflation of the summit prior to the eruption.

Figure 62. Tilt variation from the Dolomieu Sud station at Piton de la Fournaise compared between 1999, 2000, and 2001. Courtesy of T. Staudacher, OVPF.

Seismicity. Intense seismicity on Piton de la Fournaise increased early in 2001. During 20 January-10 February, 133 tremors were registered (generally M < 0.5). Then, after 13 days of calm, a new series of tremors began on 25 February that included 315 events. These events were weak (M < 1.5), but increased in intensity with respect to the events earlier in the year. On 3 March, 40 summit tremors occurred within one hour, and a total of 126 tremors were observed that day. All of these tremors took place beneath the Dolomieu crater at ~0.5 km below sea level.

The number of tremors increased again starting on 12 March and continuing until the eruption on 27 March. Tremor hypocenters measured on 23 March occurred 1.5 km below sea level, but rose the next day to 0.5 km below sea level. Seismometers recorded 145 tremors on 25 March. Tremor intensity increased gradually during the period with numerous events of M 1.0-1.9. In addition, precursory seismicity and deformation measurements were correlated as shown in figure 63. Figure 63 indicates that, in January, summit inflation preceded the first period of seismicity by about 10 days, while the second increase in inflation, which began on 24 January, occurred simultaneously with the second period of strong seismicity. The latter continued essentially until the eruption. On 27 March, 120 tremors were detected, including one at 1255 of M 2.0. At 1320, an eruption began on the SE flank. Tremor that began with the eruption on 27 March diminished regularly until 2 April; after eight days of activity, the eruption ended on 4 April at about 0700.

Figure 63. Total number of earthquakes at Piton de la Fournaise compared with tilt variation during 1 January - mid-April 2001. Note that the total number of earthquakes exceeds the scale of the figure during and after the 27 March eruption. Courtesy of T. Staudacher, OVPF.

Ground observations. Ground observations were undertaken several hours after the eruption began. Five major fissures were active; their exact positions were determined later using GPS measurements. The first fissure, ~250 m long, began 100 m below the edge of Dolomieu Sud while the last ended between Piton Morgabim and the Signal de L'Enclos. The general trend of the fissures was ESE.

Three significant aa flows were observed. The first was fed by the highest fissure and descended along the S flank ending at about 1,800 m elevation. A second flow, which began at a lower altitude, wound around the Piton Morgabim toward the S and along the path of the previous flows from the June and October 2000 eruptions. The most significant flow was fed by the lowest fissure, which went N along the path of the June and October 2000 flows and came down the Grandes Pentes. By 27 March at 1700, this flow reached an elevation of 700 m, descending to 500 m on 28 March and continuing down to 350 m elevation on 29 March. These fissures were active for only several hours, and on 28 March the eruption became concentrated on the last fissure where the cone Piton Tourkal formed during the next few days. The cone was located midway between the Signal de l'Enclos and the Piton Morgabim (figure 64).

Figure 64. Photograph showing lava flows and the future location of the soon-to-be-formed Piton Tourkal cone, between the Signal de l'Enclos (bottom left) and the Piton Morgabim (middle left). Courtesy of T. Staudacher, OVPF.

Between 27 March and 3 April, a total of nine samples were gathered for chemical analysis. On 3 April, the lava temperature was measured to be 1,150°C. No significant variation in the rates of radon emission was measured during 27 March - 3 April.

Continuous extensometer and tiltmeter variations occurred, and increased seismic activity was recorded beginning in late May. A short seismic crisis with 126 recorded events started on 11 June at 1327 and, at 1350, extensometer variations indicated that a new eruption had started on the SE flank in the same area as the 27 March eruption. En echelon fissures formed on the S flank at ~2,500 m elevation, 200 m below the Dolomieu summit crater. More fissures were located between 2,000 and 1,800 m elevation on the E flank at the southern base of crater Signal de l'Enclos and N of the Ducrot crater. Several lava flows descended the Grand Brûlé but progressed very slowly; at 1700 the front of the lava flow reached an elevation of 1,450 m. On the morning of 12 June, only the lower fissure at 1,800 m elevation was still active. It measured ~200 m long, with several lava fountains that sent material 20-30 m high. The lava flow followed the N border of the 27 March lava flow and reached about 400 m elevation on the Grand Brûlé.

Information Contacts: Thomas Staudacher and Jean Louis Cheminée, Observatoire Volcanologique du Piton de la Fournaise, Institut de Physique du Globe de Paris, Institut National des Sciences de l'Univers, 14 RN3 - Km 27, 97418 La Plaine des Cafres, Réunion, France (Email: staud@univ-reunion.fr, URL: http://volcano.ipgp.jussieu.fr:8080/reunion/stationreu2.html).

07/2001 (BGVN 26:07) 11 June-7 July eruption; two lava flows block highway

A short seismic crisis with 126 recorded events started at Piton de la Fournaise on 11 June 2001 at 1327. At 1350 extensometer variations indicated that a new eruption had started on the ESE flank, in the same area as the previous eruption on 27 March 2001. En echelon fissures started at about 2.5 km elevation on the S flank, 200 m below the Dolomieu summit caldera. More fissures were located between 1.8 and 2 km elevation on the E flank at the southern base of crater Signal de l'Enclos and N of the Ducrot crater. Several lava flows descended the Grand Brûlé but their progression was very slow; at 1700 the front of the lava flow was still located at an elevation of ~1.5 km. On the morning of 12 June, only the lower fissure at 1.8 km elevation was still active. It was ~200 m long, with several lava fountains 20-30 m high. The lava flow followed the northern border of the 27 March lava and descended to about 400 m elevation in the Grand Brûlé.

On 16 June a cone began to form and lava fountains rose up to 30 m above the surface in an area at 1.8 km elevation. An active fissure was located on the E flank at the S base of crater Signal de l'Enclos. Tremor weakened but continued under the volcano's E flank through late June. Lava fountains were visible at two vents; at one vent strong degassing occurred, while at the other vent a boiling lava lake occasionally overflowed, sending lava towards the NE. New lava flows were observed on 29 June in the Grand Brûlé area traveling to the N. On 1 July an increase in tremor occurred for about 1 hour and was accompanied by strong degassing at the cone and a strong amount of lava emission. Several dozen small flows were visible by the next day. Tremor and the intensity of local earthquakes increased during the first week of July. The earthquakes had magnitudes less than 3 and were located under Dolomieu crater at a depth near sea level. On 6 and 7 July two aa lava flows, 80 and 100 m wide and up to 5 m high, crossed the national highway in the Grand Brûlé area (see figure 65). On the afternoon of 7 July the end of the eruption was marked by the disappearance of tremor and a dramatic decrease in the intensity of local earthquakes.

Figure 65. On 6 July 2001, police and security personnel watch as molten lava from Piton de la Fournaise blocks the main national RN 2 road, which connects Réunion island from E to S.

Information Contacts: Thomas Staudacher and Georges Boudon, Observatoire du Piton de la Fournaise Institut de Physique du Globe de Paris - B89, 4 Place Jussieu, 75252 Paris cedex 05, France.

12/2001 (BGVN 26:12) Erupting fissures on 5-16 January 2002 in l'Enclos Fouqué caldera

An eruption began on 5 January 2002 and continued until 16 January. The eruption, which sent lava to the sea, followed several months of increased seismicity. The most recent previous eruption occurred during 11 June-7 July 2001 (BGVN 26:07).

Seismicity during October 2001-January 2002. During 3-9 October the Observatoire Volcanologique du Piton de la Fournaise (OVPDLF) reported that, beginning in early September, seismicity increased to ~10 events per day. Seismic activity further increased during early October, with up to 40 daily earthquakes. In the first half of October an average of 16 earthquakes per day occurred; in the second half the daily average increased to 26 events. On 5 November seismometers registered 129 earthquakes, an anomalously large number. Their hypocenters plotted at 0.62 km under the N edge of Bory Crater. In November, ~30-50 earthquakes occurred per day.

During late September through mid-October, the volcano was at Alert Level 1, and significant tilt variations were detected S of Dolomieu Crater. These events occurred simultaneously with the widening of fissures at two extensometer stations on the N and S flanks, suggesting slight summit inflation. The extensometer variations were ~3-4 times smaller than those during previous eruptions. Seismicity disappeared until the end of December, but increased again during 26-30 December when the daily earthquake counts were 17, 49, 62, and 70.

On 26 January 2002 a total of 17 earthquakes occurred, including two M 1.8 events. The earthquakes were mostly located 0.5-1.5 km below sea level, and their epicenters were beneath the N edge of Bory to Dolomieu craters. Extensometers at Magne and Chateau Fort continued to reveal slow opening of cracks, reaching 0.27 mm on 27 January.

On that same day 49 earthquakes were recorded, including events of M 2.2, 2.0, and 1.8. On 28 December during 0400-1000 a total of 48 earthquakes registered. The extensometers at Magnes and Château Fort continued to show a slow opening of the cracks. The tiltmeters, which had remained stable since the beginning of December, showed a resumption of inflation. On 29 January seismometers recorded 62 earthquakes, including an M 2.3 event. On 30 January a total of 70 earthquakes included M 2.2 and 2.0 events. Opening of the cracks at Magnes and Chateau Fort continued to progress and reached 0.28 mm.

New eruption during 5-16 January 2002. An eruption began at 2300 on 5 January and ended at 1615 on 16 January. On 5 January fire fountaining occurred and lava flowed from four cracks that opened in the NE part of l'Enclos Fouqué caldera and continued towards the foot of the Nez Coupé de Sainte Rose, a feature located on the E side of the active field of lava flows (see map showing the location of previous fissures there in BGVN 23:09). By 6 January only two cracks remained active and lava flows reached ~1,100 m elevation on the projecting ledge of the Plaine des Osmondes.

On 6 January at 2100 the eruption was visible from Piton Sainte Rose and from the National Road RN2. During 7-9 January, the eruption continued but tremor progressively decreased. On 9 January the tremor was half that of the previous day and almost no fire-fountaining was visible. Other seismicity persisted, although on 7 January only four low-magnitude earthquakes were detected. By 8 January the reading on the Château Fort extensometer had decreased only slightly since the eruption began. Readings at the Magnes extensometer continued to increase slightly.

A field excursion around this time found no further incandescent lava visibly flowing at distance from the vent areas. Observers noted that the initial flow did not extend beyond the Plaine des Osmondes. On the other hand, the interior of the eruption cone was still hot, strong degassing was audible, and small, nearly continuous projections of molten material took place, although the emitted volume was negligible.

Tremor decreased during 7-11 January. As few as 8 small shallow earthquakes were recorded per day. On 12 January tremor started to increase almost continually in comparison to the previous day, and numerous earthquakes were recorded ~4 km beneath the Plaine des Osmondes, near the N caldera wall.

During the evening of 12 January, a new fissure opened at the base of the rampart in the lower part of the Plaine des Osmondes. Lava flowed from a lava tunnel down into the Grand Brûlé close to the northern rampart. On 14 January lava flowed across the highway on its way to the ocean, entering it at 1540. By 15 January tremor was stable and 160 earthquakes were recorded over a 24-hour period on the N side of the volcano. At 0600 a swarm of low-frequency earthquakes was recorded in the NE rift zone.

After 12 days of lava emission and associated tremor, the eruption ended on 16 January, marked by a sudden, large decrease in lava emission at 1610 and the termination of tremor at 1910. After the eruption ended a large number of long-period earthquakes were recorded below the summit and the Plaine des Osmondes, indicating the continued presence of magma beneath the NE rift zone. The total lava volume emitted was estimated to be 10-15 x 106 m3.

Information Contact: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF), 14 RN3, le 27Km, 97418 La Plaine des Cafres, La Réunion, France.

11/2002 (BGVN 27:11) Fissure eruption 16 November-3 December sent lava to the sea

After 3 months of high seismicity at Piton de la Fournaise and three small seismic crises, a strong seismic crisis with several hundreds of earthquakes started on 15 November at 2336. The earthquakes were accompanied by strong deformation at the summit, including tilt of up to 300 µrad. An eruption began on 16 November at 0433 with the appearance of eruption tremor. Fissures opened on the volcano's E flank between elevations of 1,900 and 1,600 m and lava flowed down the E flank. A small cone formed on one of the most active fissures at ~1,600 m elevation. On 18 November, continuous emissions from the cone rose up to 1,600 m above the crater rim.

During 20-26 November, visual observations were largely hampered by inclement weather. Eruptive tremor was constant on the 20th and 21st, and fluctuated on the 22nd. Tremor showed short-term variations during 23-26 November. Lava flows traveled in lava tubes between the active cone and 1,200 m elevation and traveled on the land surface at elevations between about 1,200 and 500 m.

On 27 November, eruptive tremor had decreased to 25% of that seen since this eruption's start. On that day the fissures located on the S at ~1,850 m and at ~1750 m elevation were no longer active. Instead, two fissures at ~1,600 m elevation were active. The smallest and lowest produced a small lava flow. The largest fissure was located 100 m higher and slightly to the N; it emitted a significant lava flow. Sprays of lava there on 16 November reached up to 80 m high. On 17 November they reached only up to 30 m high, at least in part owing to drag imposed by a small lava lake that had then developed within the cone's interior.

On 29 November eruptive tremor increased by a factor of two, and there were 89 seismic events recorded that day. On the 30th, 329 seismic events were recorded, all located about 1 km above sea level, beneath the floor of Dolomieu crater. A lava flow in the Grand Brûlé area approached the national road, crossing it around 2300. By about 0500 on 1 December the lava flow had reached the sea. At this time almost constant seismicity occurred, with more than 1,500 earthquakes recorded with magnitudes up to 2.8. Eruption tremor was stable; numerous long-period earthquakes were also recorded, indicating the presence of magma beneath the summit. On the morning of 2 December seismicity increased by about a factor of about three, but decreased the next day.

Lava emissions from Piton de la Fournaise ended on 3 December. Permanent tremor decreased significantly that day, although seismic events beneath the summit continued at a rate of 1 per minute. Seismicity continued to decline over the next two days. Poor weather conditions prevented helicopter observations during 3-5 December. Inspection on 6 December revealed some collapses between Bory and Dolomieu craters, and white fumes were being released from the new Guanyin cone, but there was no evidence of surface activity coincident with larger seismic events that occurred while scientists from the OVPDLF were on the edge of Dolomieu.

Information Contact: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF), 14 RN3, le 27Km, 97418 La Plaine des Cafres, La Réunion, France.

02/2003 (BGVN 28:02) Infrared data from November-December 2002 eruption

Following the 16 November-3 December 2002 eruption (BGVN 27:11), the Observatoire volcanologique du Piton de la Fournaise reported on 19 December that very strong seismicity had continued at a rate of more than 1,000 earthquakes per day. The earthquakes were located a few hundred meters below Dolomieu crater.

MODIS tracking of effusive activity during 2000-2002. The November-December 2002 eruption was detected by the Hawai'i Institute of Geophysics and Planetology MODIS thermal alert system (http://modis.higp.hawaii.edu/). The eruption was apparent as a major hot spot in the SW sector of Reunion (figure 66). The first image on which activity was flagged was that of 1030 (0630 UTC) on 16 November 2002. At that point the flagged anomaly was six 1-km pixels (E-W) by 2-3 pixels (N-S). The hot spot attained roughly the same locations and dimensions on all subsequent images, where hot pixels were flagged on 16 images during November 16-3 December 2002. The exception was an image acquired at 2255 (1855 UTC) on 30 November (figure 66), on which the hot spot attained its largest dimensions of ~12 x 5 pixels. The increase in hot spot dimensions towards the end of November is also apparent in the radiance trace (figure 67). However, without examination of the raw images HIGP scientists cannot determine from the hot spot data alone whether this recovery was due to an increase in activity or an improvement in cloud conditions. This was the 6th eruption of Piton de la Fournaise tracked by the MODIS thermal alert (Flynn et al., 2002; Wright et al., 2002) since its inception during April 2000 (figure 68).

Figure 66. Hot-spot pixels flagged at Piton de la Fournaise by the MODIS thermal alert at 0630 UTC on 16 November 2002 (top) and 1855 UTC on 30 November 2002 (bottom). Courtesy of the HIGP Thermal Alerts Team.
Figure 67. Piton de la Fournaise hot spot radiance detected by MODIS during 15 November-5 December 2002. Courtesy of the HIGP Thermal Alerts Team.
Figure 68. Piton de la Fournaise hot spot radiance detected by MODIS during April 2000-December 2002. Courtesy of the HIGP Thermal Alerts Team.

References. Wright, R., Flynn, L.P., Garbeil, H., Harris, A.J.L., and Pilger, E., 2002, Automated volcanic eruption detection using MODIS: Remote Sensing of Environment, v. 82, p. 135-155.

Flynn, L.P., Wright, R., Garbeil, H., Harris, A.J.L., and Pilger, E, 2002, A global thermal alert using MODIS: initial results from 2000-2001: Advances in Environmental Monitoring and Modeling (http://www.kcl.ac.uk/kis/ schools/hums/geog/advemm.html), v. 1, no. 3, p. 5-36.

Information Contacts: Observatoire volcanologique du Piton de la Fournaise, 14 RN3, le 27Km, 97418 La Plaine des Cafres, La Réunion, France (Email: Thomas.Staudacher@iremia.univ-reunion.fr); Andy Harris, Luke Flynn, Harold Garbeil, Eric Pilger, Matt Patrick, and Robert Wright, HIGP Thermal Alerts Team, Hawai'i Institute of Geophysics and Planetology (HIGP) / School of Ocean and Earth Science and Technology (SOEST), University of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (http://hotspot.higp.hawaii.edu/, Email: harris@higp.hawaii.edu).

05/2003 (BGVN 28:05) Eruption on 30 May generates lava flows within Dolomieu crater

Eruptions are common at Piton de la Fournaise, with the most recent activity occurring in January 2002 (BGVN 26:12) and November-December 2002 (BGVN 27:11). At the end of the November 2002 eruption, seimicity beneath Dolomieu crater increased from 28 November to 23 December. On 22 December there were 5,700 seismic events recorded. At 1002 on 23 December a magnitude 3 event occurred and seismicity stopped. The next day a new crater was observed in the SW part of the larger Dolomieu crater.

Since March 2003, the extensometer network and GPS measurements had indicated inflation of Piton de la Fournaise. A new eruption began on 30 May within Dolomieu crater. The eruption proceeded in multiple phases through at least 24 June; activity through 6 June is reported below.

Seismicity increased slightly on 28 May. At 1137 on the morning of 30 May a seismic crisis began that lasted 17 minutes with a total of 34 events. Tremor appeared at 1155 beneath Dolomieu crater, and an eruption started within the pit crater formed on 23 December 2002. Lava fountaining was observed until 1400, after which most surface activity stopped. A lava flow ~400 m long and 250 m wide extended into the W part of Dolomieu. The total volume of lava emitted during the 30 May activity was estimated to be 0.2-0.3 x 106 m3. Seismicity beneath the crater continued, with intermittent weak tremor being registered through 3 June. No deflation was detected, and there was strong degassing in the collapse area.

On 4 June at 1155 the eruption started again from the same site, enlarging the lava flow in the W part of Dolomieu crater. Lava fountains reached 15 m in height. Steady lava emission continued into 6 June (figures 69 and 70). Volcanic tremor remained stable until the morning of 6 June, when a decreasing tendency was noted. After a short phreatic eruption, the second phase of this eruption stopped on the evening of 6 June. The lava-flow field had grown to ~600 x 400 m in size by that time (figure 71).

Figure 69. Photograph of the SW part of Dolomieu crater at Piton de la Fournaise at 0812 on 6 June 2003 showing the active vent and part of the recent lava-flow field. View is towards the W. Courtesy of OVPF.
Figure 70. Photograph of the W part of Dolomieu crater at Piton de la Fournaise at 0850 on 6 June 2003 showing the active vent and most of the recent lava-flow field. View is towards the SW. Courtesy of OVPF.
Figure 71. Topographic map of Dolomieu crater at Piton de la Fournaise showing the extent of the lava-flow field on 30 May and 6 June 2003. Elevations are in meters, and the Gauss-Laborde Piton des Neiges system is used for the map coordinates. Courtesy of OVPF.

Information Contacts: Observatoire volcanologique du Piton de la Fournaise (OVPF), Institut de Physique du Globe de Paris, 14 RN3, le 27Km, 97418 La Plaine des Cafres, La Réunion, France (Email: Thomas.Staudacher@univ-reunion.fr).

06/2003 (BGVN 28:06) Lava flows in Dolomieu crater; eruption ends 7 July

Reports from the Observatoire Volcanologique du Piton de la Fournaise (OVPF) indicated ongoing eruptive activity from late May to 6 June 2003 (BGVN 28:05). The activity was characterized by sporadic seismicity, degassing from fissures, and lava flows. Inflation of Piton de la Fournaise was observed beginning in March 2003, without later indications of deflation as of July 2003. Eruptive activity within Dolomieu crater continued until 7 July.

Eruptive tremor had completely disappeared by 8 June, and on the 10th that phase of the eruption was considered to be finished. About thirty small earthquakes were observed, caused by minor collapses. The extensometric network continued to show an opening of cracks at Magne and Chateau-Fort. On 10 June, 71 earthquakes were observed, the strongest of which had magnitudes of 1.4-2.0. The earthquakes were located ~400 m under Dolomieu in the SW part near the site of the 30 May-4 June eruption. Extensometers continued to indicate swelling of the volcano, but no summit inflation was observed during the eruption.

On 13 June at 0308 new eruption tremor appeared within Dolomieu crater. A helicopter overflight confirmed that the eruption continued from the same site as the first two eruptive phases. Such a scenario was expected because the extensometer network showed continuous opening of the monitored fissures. Seismicity on 12 June had decreased compared to the previous two days, with a lack of very low amplitude earthquakes. That day eruptive tremor began without being preceded by even a small earthquake.

During the morning of 14 June eruption tremor was stable and practically constant; other seismic events did not register. On 15 June at 0600, the tremor entirely disappeared. Crater observations showed that lava flows had extended to the N wall of Dolomieu crater, covering almost half of the crater floor as of 16 June (figure 72). After a cessation of several days, the eruption began again on 21 June at about 2330. After a progressive increase of tremor in the hours that followed, the situation stabilized, and the tremor then strongly decreased.

Figure 72. Topographic map of Dolomieu crater at Piton de la Fournaise showing the extent of the newly erupted lava-flow field on 30 May, 6 June, 7 June, and 16 June 2003. Elevations are in meters, and the Gauss-Laborde Piton des Neiges system is used for the map coordinates. Courtesy of OVPF.

On 24 June the eruption was still in progress. The tremor increased strongly in the night and reached the maximum level of the preceding eruptive phases. Observations on 26 June showed two small openings in front of the principal cone. The first showed degassing, and the second, which was almost closed, emitted sporadic weak projections. Within 100 m of the cone an emission of a very fluid and degassed lava had produced significant flows. On 27 June the tremor had strongly diminished.

After 0630 on 28 June highly variable tremor related to "gas pistons," or regular degassing, was observed on a scale not previously seen at Piton de la Fournaise. Some lava flows in Dolomieu remained active. A small cone opposite the Piton kaf degassed strongly in time with the other gas explosions.

On 1and 2 July, no change in eruptive activity was observed. The tremor varied with a time interval of 12-13 minutes between total stop and maximum tremor amplitude. The eruption continued on 3 July, but on 4 July the tremor had diminished, and the tremor variations observed in past days were less pronounced. No lava projections were seen in the crater during this phase, and volcanic earthquakes were not detected until one occurred on 3 July. The eruption ended on 7 July.

Information Contacts: Observatoire Volcanologique du Piton de la Fournaise (OVPF), Institut de Physique du Globe de Paris, 14 RN3, le 27Km, 97418 La Plaine des Cafres, La Réunion, France (URL: http://volcano.ipgp.jussieu.fr:8080/reunion/stationreu2.html, Email: Thomas.Staudacher@univ-reunion.fr).

08/2003 (BGVN 28:08) Lava eruption from three fissures during 22-27 August

Five months of slow inflation at Piton de la Fournaise and the eruptive series that occurred between May and July 2003 (BGVN 28:05 and 28:06) were followed by new activity in August. Ongoing eruptions in June at the Dolomieu crater had ceased by mid-July, but at 1848 on 22 August seismic activity was again detected beneath the crater. Around 2120 that night an eruptive fissure opened in the Bory crater (adjacent to Dolomieu on the W), followed at 2210 by a second fissure at ~2,450-2,470 m elevation on the N flank. Both fissures remained active for a short time.

At 2330 a final fissure opened on the N flank ~250 m below the second fissure, at 2,200 m elevation. Most of the activity was focused at this third fissure, opening a new crater ~50 m E of the 1998 Piton Kapor crater. During this activity on 22 August lava flowed down into la Plaine des Osmondes. The 36 hours following the initial activity were characterized by a substantial increase in tremor intensity and lava emissions, but by 2152 on 27 August the eruption abruptly ceased. A series of long-period events were observed after 27 August through at least 1 September.

Information Contacts: Observatoire volcanologique du Piton de la Fournaise, Institut de Physique du Globe de Paris, 14 RN3, le 27Km, 97418 La Plaine des Cafres, La Réunion, France (Email: Thomas.Staudacher@univ-reunion.fr).

09/2003 (BGVN 28:09) Seismic crisis and a new SSW-flank fissure on 30 September

A seismic crisis started at 2225 on 30 September 2003 beneath the SW corner of Dolomieu crater ~ 2 km below the summit. At 2330 eruption tremor appeared and was localized beneath the SSW flank of Piton de la Fournaise. A straight 400-m-long fissure opened at 2,350 m elevation. The eruption tremor reached a maximum at 0100 on 1 October and declined after 0200, disappearing completely at 1300.

Since March 2003, the extensometer network and GPS measurements had indicated inflation of Piton de la Fournaise. A new eruption that began on 30 May within Dolomieu crater proceeded in multiple phases through 7 July, followed by new activity through 27 August (BGVN 28:05, 28:06, and 28:08).

Information Contact: Thomas Staudacher, Observatoire Volcanologique du Piton de la Fournaise Institut de Physique du Globe de Paris, 97418 La Plaine des Cafres, La Réunion, France (URL: http://volcano.ipgp.jussieu.fr:8080/reunion/stationreu2.html, Email: Thomas.Staudacher@univ-reunion.fr).

03/2004 (BGVN 29:03) December 2003 lavas spread across 40% of Dolomieu crater floor

BGVN 28:09 reported a seismic crisis and new SSW-flank fissure at Piton de la Fournaise on 30 September 2003. The Volcanological Observatory monitoring Piton de la Fournaise and the local press reported a further seismic crisis that developed on 7 December 2003 at 1429 beneath the summit. Following around an hour of seismicity, an eruption began on 7 December at 1535 in the Dolomieu crater, with lava fountaining to ten's of meters from two fractures on the SE crater floor. Two new fractures were also observed on the S crater rim that did not produce lava. The eruption decreased rapidly over the night of 7-8 December. By 8 December at about 1400 small incandescent lava flows and rock falls on the S crater wall were observed. By the night of 8 December the eruption ceased but strong degassing and fluctuating seismicity continued. New lava covered ~ 40% of the Dolomieu crater floor.

The eruption was preceded by a seismic swarm on 6 November that was followed by ~ 30 cm of steady uplift and 10-20 earthquakes recorded per day. As of 16 December, significant seismic activity continued, and hikers were permitted only limited access. Press reports indicated three quite active cones within the S rampart of the Dolomieu crater, surrounded by ejecta found more than 200 m N, noisy degassing, lava covering the bottom of the crater up to 5 m thick, and zigzag cracks crossing the crater's S exterior.

A further seismic event with significant surface deformation occurred over 7-9 January 2004.

[On 9 January eruption tremor started near Nez Coupé de Sainte Rose. A 300-m-long fissure, cutting the 1931 crater, produced a small ~2-km-long lava flow. The eruption stopped on 10 January around 1200.]

Information Contact: Thomas Staudacher, Observatoire Volcanologique du Piton de la Fournaise Institut de Physique du Globe de Paris, 97418 La Plaine des Cafres, La Réunion, France (URL: http:\\volcano.ipgp.jussieu.fr:8080\reunion\stationreu2.html, Email: Thomas.Staudacher@univ-reunion.fr).

05/2004 (BGVN 29:05) Elevated April seismicity followed by eruptive fissures and lava flows

After the eruption of December 2003 (BGVN 29:03), Piton de la Fournaise underwent a month of high seismic activity in April 2004. The activity consisted of 10-30 earthquakes per day with two minor seismic crises, and was accompanied by continuous inflation of the summit. On 2 May a new seismic crisis started at 1903. At 1936 eruption tremor appeared. The high intensity of tremor near the Bory crater (2,632 m) indicated that eruption had most likely started within or very close to the crater.

No activity was visible in the crater on 3 May. An overflight planned by the Observatoire Volcanologique du Piton de la Fournaise (OVPF) with the help of local police militia was unable to take place due to bad weather and rain on the volcano. The initial assessments of the observatory indicated the opening of eruptive cracks in the higher of the two craters. A long crack on the SW side extended from 2,500 m to at least 2,300 m elevation. During an observational visit by OVPF volcanologists on 4 May, a fissure was observed to have opened between 2,800 m and 2,200 m elevation. The fissure was inactive at the time of observation but much lava ejecta covered the surrounding area. A second fissure, opened during the night between Sunday and Monday, was active. As of 4 May, activity continued from three eruptive vents located between Chateau-Fort crater and Piton Bert. Tremor remained stable. During the night of 11-12 May, the single remaining active fissure projected lava ejecta onto the slopes of the cone in the SW area of the crater. The eruption continued on 15 May but moved from the summit of the volcano toward its lower slopes. Flows accumulated within the crater, and a large flow with an estimated length of 300 m was seen coming from a ~ 2.5 km-long tunnel, originating at the floor of the Enclos Fouqué caldera and issuing at the surface near the Nez du Tremblet and in the Grandes Pentes area. Further downslope, burning vegetation was observed, indicating the presence of lava flows far from the point of emission. The larger flow reached an elevation of 1,150 m, putting it 4 km from National Route (NR) 2. At 1200, the lava flow was 2.5 km from NR 2. Scientists at the observatory expected the flow's advance to slow due to the shallowing of the slope starting at 900 m elevation, and because the eruptive tremor, though it had increased slightly the day before, remained at a moderate level.

On 16 May, the lava flow stopped 1.8 km from NR 2 at 460 m elevation. A second fissure produced a second lava flow parallel to the first. Tremor increased in the crater, indicating a renewal of activity, and lava ejecta were erupted from the two cones. The OVPF reported on 17 May that the eruption was still continuing. Lava fountains from the main eruptive cone rose several tens of meters above the vent. That evening, lava flows were visible on the upper part of the Grandes Pentes. Pélé's hair had fallen in the town of St. Rose. Seismicity remained on a moderate level. At about 1500 on 18 May, the OVPF's network recorded a progressive increase in the tremor over a twenty-minute period; then at 1552, the tremor decreased dramatically. By 1615, any trace of tremor had disappeared from the recordings. On 21 May at 1500, a lava front was observed flowing at 1150 m elevation, within ~4 km of National Route 2. Volcanic tremor increased slightly, but remained at a moderate level.

Information Contact: Thomas Staudacher, Observatoire Volcanologique du Piton de la Fournaise Institut de Physique du Globe de Paris, 97418 La Plaine des Cafres, La Réunion, France (URL: http://volcano.ipgp.jussier.fr:8080/reunion/staionreu2.html, Email: Thomas.Staudacher@univ-reunion.fr).

12/2004 (BGVN 29:12) August-October eruption sends lava flows to the sea; pillow lavas

Inflation over the last year and a half, monitored by permanent GPS stations, has not been interrupted by six eruptions over this period, the latest during 2-18 May 2004 (BGVN 29:05). Increased seismicity and ground deformation reported by the Observatoire Volcanologique du Piton de la Fournaise (OVPDLF) in late June 2004 continued through 9 August when the seismic network recorded 50-70 low-intensity earthquakes. The third eruption of 2004 started on 13 August. Increasing seismicity and fissure opening had occurred since early July 2004. At 0240 in the morning of 13 August, a 25-minute seismic crisis beneath the summit preceded the opening of an ~ 500-m-long E-W fissure within Dolomieu crater, with the fissure continuing on the E flank to an elevation of 1,900 m. The main activity was located at 2,150 m elevation. A significant lava flow ran down the "Grandes Pentes."

Ten days after the beginning of the eruption, ~ 750 m of National Road 2 was overrun, and on 25 August lava from an 8.5-km-long system of lava tubes entered the sea. A 670-m-long, 320-m-wide platform was build up within several days, representing more than 2 x 106 m3 of material. A second smaller platform was build up in the following days by nearby lava flows entering the sea. Two small hornitos, up to 8 m high, formed on the seaside edge of the first platform. The main eruption phase stopped on 2 September. However, significant phreatic activity continued on the new platform and was followed by two minor phases from the main vent on the E flank, the last one stopping at about 0300 on 4 October. Formation of pillow lava was recorded by professional divers for the first time at île de la Réunion, at a water depth of 50 m in front of the new platform.

The Toulouse Volcanic Ash Advisory Center reported noteworthy eruptive activity beginning on 4 September, following the end of the main eruption phase. Ash reportedly fell near the volcano's summit, and a lava flow entering the sea produced a steam and ash plume that rose ~ 2 km. Emissions ceased on the morning of 7 September.

Information Contacts: Thomas Staudacher, Observatoire Volcanologique du Piton de la Fournaise Institut de Physique du Globe de Paris, 97418 La Plaine des Cafres, La Réunion, France (URL: http://volcano.ipgp.jussieu.fr:8080/reunion/stationreu2.html, Email: Thomas.Staudacher@univ-reunion.fr); Toulouse Volcanic Ash Advisory Center (VAAC), Météo-France, 42 Avenue G. Coriolis, 31057 Toulouse Cedex, France (Email: vaac@meteo.fr, URL: http://www.meteo.fr/aeroweb/info/vaac/homepage/eindex.html).

11/2005 (BGVN 30:11) Eruption on 5 October follows four months of heightened activity

Increased seismicity and ground deformation from late June 2004 through 9 August preceded the third eruption of 2004, which started on 13 August (BGVN 29:12). During that eruption ~ 750 m of National Road 2 was overrun by lava. Eruptive activity ceased on the morning of 7 September 2004 (BGVN 29:12). Eruptions occurred again during February and October-December 2005.

Eruption during February 2005. A new period of heightened seismicity began on 17 February 2005 around 1300, consisting of about 100 seismic events within 90 minutes. After that, the number of events decreased, but recommenced at 1638 with several hundred events. Strong deformation was recorded at the same time by tiltmeters and the extensometer network. Eruption tremor began around 2035, becoming strong at 2050. The eruption site seemed to be situated close to Nez Coupé de Sainte Rose (on the N side of the volcano), and lava flows were observed in the Grand Brûlé area.

After a period of relative quiet on 19 February, eruption tremor increased to high levels again on 21 February. Two eruption sites were active: the principal vent at 1,600-m elevation above the Plaine des Osmondes, and a vent at about 1,200-m elevation in the Plaine des Osmondes. The principal vent released a volcanic plume and several pahoehoe lava flows, but no lava fountains were visible. The second vent also released a very fluid pahoehoe lava flow. The flows covered a large area within the Plaine des Osmondes, and smaller lava flows traveled to about 600-m elevation in the Grand Brûlé.

On 24 February, shallow seismicity began beneath Dolomieu crater. It increased over time and by 26 February, several hundreds of seismic events up to M 3 occurred. According to the Observatoire Volcanologique du Piton de la Fournaise (OVPDLF), these events may have indicated formation of a new pit crater within Dolomieu crater. On 24 February, visible signs of activity stopped within the Plaine des Osmondes, while eruption tremor slowly increased.

On the evening of 25 February, a lava flow from Plaine des Osmondes traveled down the Grandes Pentes, cutting the National Road on its way to the sea. The lava flow covered a distance of ~ 5 km in about 2 hours. At the same time, seismicity increased on the NE rift zone above Bois Blanc, and a new vent opened within the Trou de Sable on the N border of the caldera at 450-m elevation. This vents lava flow stopped about 100 m from the National Road.

Eruptions during October-December 2005. Another eruption started on 4 October 2005 at 1426 after 4 months of almost continuous inflation and increased seismicity. The eruption was immediately preceded by a 56-minute-long sequence of seismicity and strong summit inflation. A low-intensity eruption at Dolomieu crater produced pahoehoe lava flows that covered a small area of the western part of the crater.

Immediately after the end of the 4 October eruption at Dolomieu crater, the permanent GPS network and extensometer network continued to show strong surface deformation, which was a precursor for a new eruptive event. On 29 November 2005 at 0559 a seismic crisis began, and at 0625 tremor indicated the beginning of an eruption. A vent opened in the western part of Dolomieu crater and another vent opened on the N flank. Very little projected volcanic material was visible. A large, fast-moving lava flow traveled down the N flank in the direction of Piton Kapor. Inclement weather prohibited further observations. The Toulouse VAAC reported that ash from the eruption was not visible on satellite imagery.

Following the 29 November eruption, further summit inflation was recorded by the permanent GPS network. On 26 December at 1444 a seismic crisis started beneath Dolomieu crater. Within the next 2 hours seismic activity shifted to the NE, towards Nez Coupé de Sainte Rose. A first fissure opened at 1715 at the NE base of Piton de la Fournaise; at 2200 eruptive fissures opened in the caldera wall about 500 m E of Nez Coupé de Sainte Rose and lava flowed into the Plaine des Osmondes. By 28 December, eruptive activity was almost constant. An aa-type lava flow crossed the Grandes Brûlé and reached a point 3 km upslope from the national road.

Information Contacts: Thomas Staudacher, Observatoire Volcanologique du Piton de la Fournaise, Institut de Physique du Globe de Paris, 14 RN3 le 27 ème km, F-97418 La Plaine des Cafres, La Réunion, France (URL: http://volcano.ipgp.jussieu.fr:8080/reunion/stationreu2.html, Email: Thomas.Staudacher@univ-reunion.fr); Toulouse Volcanic Ash Advisory Center (VAAC), Météo-France, 42 Avenue G. Coriolis, 31057 Toulouse Cedex, France (Email: vaac@meteo.fr, URL: http://www.meteo.fr/aeroweb/info/vaac/).

06/2006 (BGVN 31:06) Eruption on 20 July 2006 after months of seismicity

Piton de la Fournaise exhibited dynamic activity in February and October-December 2005 (BGVN 30:11). This report covers January to July 2006. According to the Observatoire Volcanologique du Piton de la Fournaise (OVPF), following the 2005 activity was an eruptive period during 3-18 January 2006. During this time there were lava flows leaving the Plain of Osmondes and descending into the Grandes Pentes.

Seismicity was low from mid-January through March. From March until mid-July, seismicity gradually increased (figure 73), reaching 80 earthquakes on 2 July. From 1 March to the end of June, instruments detected up to 5 cm of horizontal movement at many stations (figure 74).

Figure 73. Daily earthquakes at Piton de la Fournaise during 1 March to 1 July 2006. Courtesy of OVPF.
Figure 74. Plot of the horizontal movement of Piton de la Fournaise's stations from 1 March to the end of June 2006. All of the stations had moved horizontally except for BONG, which had shifted in a circular motion during the months of observation. Station SNEG had the greatest horizontal shift, up to 5 cm. Courtesy of OVPF.

Although there was a decrease in seismicity on 17 July, on 20 July at 0218 seismicity spiked. At 0400, the summit began erupting (figure 75). A 50-m-long fissure opened on the SW flank and a lava flow went E of Rivals crater. A second 50-m-long fissure opened on the S flank between Rivals and Fort Chateau craters.

Figure 75. Lava flows and eruptive processes at Piton de la Fournaise, July 2006. The scanty available information about the photos is discussed below. a) Lava flow on the morning of 20 July 2006, the first day of the eruption; courtesy of A. Peltier, OVPF. b) Spattering cone on 24 July 2006; courtesy of T. Staudacher, OVPF. c) Cone at the main vent on the morning of 25 July 2006; courtesy of A. Peltier, OVPF. d) Erupting cone (date undisclosed); courtesy of Serge Gelabert.

On 24 July a small pyroclastic cone formed and lava fountains were visible (figure 75). One lava flow destroyed a new seismic station near Fort Chateau. On 31 July, a 200-m-long lava flow was visible S of the erupting cone. The eruption continued through the end of July. Figure 75 presents a series of photos from the eruption.

Information Contacts: Observatoire Volcanologique du Piton de la Fournaise (OVPF), Institut de Physique du Globe de Paris, 14 route nationale 3, 27 ème km, 97418 La Plaine des Cafres, La Réunion, France (URL: http://www.ovpf.univ-reunion.fr/); Serge Gélabert, 85, rue juliette Dodu, 97400 Saint-Denis, Ile de La Réunion (Email: gelabert.serge@wanadoo.fr, URL: http://www.gelabert.com).

01/2007 (BGVN 32:01) Extruding lava flows during 28 July-14 August 2006

This report extends reporting of the Observatoire Volcanologique du Piton de la Fournaise (OVPF) and covers the period from 28 July 2006 to 22 February 2007.

At 0400 on [20 July] a tremor recorded by the Bory seismic station was interpreted as the start of an eruption. Subsequent observation noted a fissure had opened between 2,380 m and 2,250 m elevation on the SW flank. A lava flow went down E of Rivals crater. At 0540 a second 50-m long fissure opened at the 2,150 m elevation on the S flank between Rivals crater and "Château Fort" that began building a small cone, and producing a 2-km-long lava flow.

Fifteen days after the initial eruption began on 20 July, activity at the cone which was slowly developing at 2,150 m elevation on the S flank almost ceased; however it continued to emit a visible plume and the OVPF reported "a considerable" degasification. The eruption, which had started on 20 July, stopped at 2300 local time on 14 August. The total lava output was estimated to be 2-3 x 106 m3.

On 30 August, a small seismic event occurred at 1000 hours, and a summit eruption started from the SSE edge of Dolomieu Crater at 1135. A fissure opened on the crater floor, and a large portion of the crater floor was covered with lava by the afternoon. A second fissure opened just outside of the crater and produced a lava flow on the E flank. On 9 Oct, a second vent, formed about 100 m SW of the first one, which was still active.

The eruption continued through the middle of October, within the Dolomieu Crater. A new cone about 20-25 m high was formed in the SE part of Dolomieu, and lava flows up to 10 m thick filled up 75% of the crater floor. The E part of the crater was filled up to the rim and lava flowed over and down the flank for hundreds of meters.

Between 25-26 November a hornito grew in the center of Dolomieu crater. After 27 November, a new overflow of the Dolomieu crater started and a 4 to 5 m diameter lava tube drained lava to the Piton de la Fournaise east flank and fed a ~ 2.5 km long lava flow that passed south of crater Jean, but did not reach the "Grandes Pentes."

As of 14 December, OVPF reported that the eruption, which had started on August 30, was continuing (then 3.5 months). A second 25-m-high crater, named Piton Moinama, formed within Dolomieu about 100 m SSW of the first crater, Piton Wouandzani. Abundant lava flows totally covered Dolomieu crater floor again with a 10-30 m deep and reached the eastern border of the crater. Several small lava flows overflowed the rim but never reached more than 100-200 m long.

On 22 December, tremor signals increased, and a third eruptive vent opened on the evening of 27 December between Piton Wouandzani and the Piton Moinama. On 2 January 2007 OVPDLF reported that the eruption of Piton de la Fournaise that began on 30 August 2006 was believed to have ceased on 1 January.

On 18 February, after a "seismic event" that began at 1611, and which lasted only a few minutes, the summit inclinometers indicated strong inflation. A new eruptive phase began at 1638 that afternoon. The exact location of the eruption was not determined; however, the signals recorded at the observatory most probably place it at the summit. The cessation of volcanic tremor the next day at 0155 marked the end of the eruption. A fissure that crossed Dolomieu crater from the west was seen during an aerial observation on 18 February.

On 19 February, seven small (M 0.7) seismic tremors were recorded at the summit. On 22 February, a fissure was observed halfway up the E side of the summit cone.

Information Contacts: Thomas Staudacher, Observatoire Volcanologique du Piton de la Fournaise, Institut de Physique du Globe de Paris, 14 route nationale 3, 27 ème km, 97418 La Plaine des Cafres, La Réunion, France (URL: http://www.ovpf.univ-reunion.fr/); Serge Gélabert, 85, rue juliette Dodu, 97400 Saint-Denis, Ile de La Réunion, France (Email: gelabert.serge@wanadoo.fr, URL: http://www.gelabert.com).

12/2007 (BGVN 32:12) Caldera collapse in April 2007; large E-flank lava flows

A caldera collapse occurred at this massive, dynamic shield volcano during early April 2007, displacing the 0.8 x 1.1 km floor of the elliptical Dolomieu caldera downward by ~ 330 m (figure 76). This was both the largest collapse at this volcano since 1760, and one of the few large collapse events seen at this volcano. Worldwide, such events are rarely documented by eyewitness or instrumental observations, with best known examples of collapses including those in 1968 at Fernandina (Simkin and Howard, 1970) and in 2000 at Miyake-jima (Kaneko and others, 2005).

Figure 76. Maps taken from Michon and others (2007) showing location and key geography of Piton de la Fournaise volcano on Reunion island. The inset shows the volcano at the island's E end and indicates the volcano's two major NE- and SE-trending rift zones (NERZ and SERZ). The larger map indicates major features, including the Bory and Dolomieu craters (arrows with heads to respective crater rims), two seismic stations, GPS station SNEG, and key vents in the 30-31 March and April eruptive episodes (1, and the main vent, 2). Note the scales on the frame indicate distance in kilometers.

The collapse at this Piton de la Fournaise occurred in association with the early stages of one of the largest historical discharges of lava flows ever seen here. The resulting lavas traveled E to reach the sea where they built a delta. Concurrent with collapse, the seismicity and deformation were cyclic in nature, suggesting collapse proceeded in a step-by-step manner. These and other events are explained by in a recent paper by Michon and others (2007), the source used to compile this report. Our last report, BGVN 32:01, discussed events through 22 February 2007.

Piton de la Fournaise has undergone intense eruptive activity since 1998, with two to four eruptions per year typically venting at the summit and proximal areas. Five distal eruptions occurred during 1998-2007, chiefly concentrated along the NE rift zone, and in particular, on the Plaine des Osmondes. Pahoehoe lava flows had completely filled Dolomieu's floor, accumulating during an August 2006-January 2007 eruption to a thickness of 20-30 m.

Prelude to collapse. On 26 February 2007 seismicity started below the summit zone. It progressively increased and over 100 events took place daily during 28-30 March. Seismicity reached anomalously high levels on 30 March at 2025 local time. About 2.4 hours later, a fissure began erupting at 1,900 m elevation SE of Dolomieu and Bory craters and the central cone (at the point labeled 1, figure 76). Discharges continued for 10 hours. Tremor ceased early the next day.

The 30-31 March eruption included lava fountains up to 50 m in height feeding voluminous lava flows. This event was the debut of a new phase of volcanism that presaged the Dolomieu caldera collapse seen in April.

Collapse. A new eruptive phase began 2 April, venting at ~ 600 m elevation ESE of the central cone (at point 2, figure 76). The venting took place along a NW-trending, 1-km-long fissure.

During the next few days, seismicity rates rose to ~ 3-fold larger than in the previous (26 February) episode. As seismicity grew on 5 April, the permanent GPS instrument SNEG situated just NE of Bory crater's rim (figure 76) started to displace inward. The vertical component of motion began with a jolt around noon and markedly progressed during 1900-2300. Next, at 0048 the next day, an Md 3.2 earthquake occurred below the summit (Bory) crater. After that earthquake, seismic station Takamaka (Tkr, figure 76) registered a signal increase of ~ 50%. Coincident with the earthquake, the GPS instrument displaced ~ 15 cm outward. What followed was a series of cyclic deformation events, episodes composed of displacements progressively inward followed by ones sharply outward.

The displacements linked closely to a series of cyclical seismic and tremor episodes. Each of those consisted of a sharp, post collapse tremor increase, followed by intervals of stable tremor. Many of these initial tremor cycles occurred on roughly two-hour intervals (through the first hours of 6 April), but gradually (with approach to dawn on 6 April) these cycles occurred at about half-hour intervals. On 6 April there occurred a paroxysmal phase during which 200 m high lava fountains vented.

Tremor descended to initial levels before the paroxysmal phase, but cyclical seismic signals remained until 0100 on 7 April. Venting continued until 1 May, accompanied then by fluctuating tremor.

Estimating the volume of lava emitted was complicated by abundant lava having entered the sea at the coast, where it built a large platform, but based on topography and bathymetry before and after the event, the authors' rough estimate, in millions of cubic meters, was ~ 100-140. This makes this one of the most voluminous eruptions at this volcano during the 20th and 21st centuries (figure 77).

Figure 77. Lava flows at Piton del la Fournaise during the eruption of 6 April 2007. Courtesy of OVPF.

Collapse morphology and structure. The first summit zone observations on the afternoon of the 6th (~ 16 hours after the beginning of the seismic cycles) revealed that the previous geophysical observations and intense eruptions coincided with caldera collapse (figure 78). The 6 April collapse affected the Dolomieu's N part, descending the zone shaded in figure 78b along sub-vertical scarps to the E, N, and W, with a net offset of 200-300 m. The pre-existing floor remained intact on the E and S, forming arc-shaped plateaus there.

Figure 78. Piton de la Fournaise's Dolomieu caldera depicted in sketch maps both prior to the April 2007 eruption and at two stages during the eruption. The first part (a) represents 31 October 2006. The arrow indicates a fracture network (Carter and others, 2007). After Michon and others (2007).

On 10 April the caldera had enlarged to engulf most of the Dolomieu structure. It had deepened to a maximum offset (determined from triangulation and confirmed with ASTER stereo images) of 320 to 340 m. Perched plateaus were restricted to the indicated zones. Subsequent morphologic changes were minor. The post-collapse caldera had diameters of 800 x 1,100 m and encompassed 82 x 104 m2, an area 11% larger than it was prior to the April eruptions.

The authors estimated that the post-collapse caldera's downward movement displaced a volume of 100-120 million cubic meters. This displacement was comparable to their estimated volume of emitted lava (~ 100-140 million cubic meters). The initial stage of collapse (seen 6 April; figure 78b) accounted for ~ 80% of the total volume displaced in the offset.

The April collapse may have followed pre-existing arcuate faults. It may also have described a magma chamber, the size and location of which were recently determined from a GPS inversion (Peltier and others, 2007). That study suggested a shallow chamber with diameters of 1.4 km and 1.0 km in the respective E-W and N-S directions.

References. Kaneko, T., Yasuda, A., Shimano, T., Nakada, S., and Fujii, T., 2005, Submarine flank eruption preceding caldera subsidence during the 2000 eruption of Miyakejima Volcano, Japan: Bull. Volcanol., v. 67, p. 243-253, doi: 10.1007/s00445-004-0407-1.

Michon, L., Staudacher, T., Ferrazzini, V., Bachélery, P., and Marti, J., 2007, April 2007 collapse of Piton de la Fournaise: A new example of caldera formation: Geophysical Research Letters, v. 34, p. L21301, doi:10.1029/2007GL031248,2007.

Peltier, A., Staudacher, T., and Bachélery, P., 2007, Constraints on magma transfers and structures involved in the 2003 actity at Piton de La Fournaise from displacement data: J. Geophys. Res., v. 112, p. B03207, doi: 10.1029/2006JB004379.

Simkin, T., and Howard, K. A., 1970, Caldera collapse in Galapagos Islands, 1968: Science, v. 169, p. 429-437.

Information Contacts: Laurent Michon and Patrick Bachélery, Laboratoire GéoSciences Réunion, Institut de Physique du Globe de Paris, Université de La Réunion, CNRS, UMR 7154-Géologie des Systèmes Volcaniques, La Réunion, France; Thomas Staudacher and Valérie Ferrazzini, Observatoire Volcanologique du Piton de la Fournaise, Institut de Physique du Globe de Paris, 14 route nationale 3, 27 ème km, 97418 La Plaine des Cafres, La Réunion, France (URL: http://ovpf.univ-reunion.fr/); Joan Marti, Institute of Earth Sciences "Jaume Almera," Consejo Superior de Investigaciones Cientificas, Barcelona, Spain.

02/2009 (BGVN 34:02) Quiet after April 2007 eruption; new eruption in September 2008

This report summarizes the caldera collapse and extensive lava effusion at Piton de la Fournaise (PdF) during May-June 2007 and events beginning in August 2008, which led to a new eruption on 12 September 2008. Additional eruptive activity and unrest continued into January 2009.

Observations from 2007. A caldera collapse during early April 2007 (BGVN 32:12) deepened and enlarged to a depth of 350-360 m to engulf most of the Dolomieu crater floor. Peltier and others (2007; and in press) noted that the area of collapse encompassed 82 x 104 m2, an area 11% larger than the crater prior to April 2007. Post-collapse calculations by the Observatoire Volcanologique du Piton de la Fournaise / Institut de Physique du Globe de Paris (OVPDLF/IPGP) indicated that the caldera's downward movement involved a volume of 120 million cubic meters. On the SE flank lava flows up to 30-40 m thick and covered an estimated 4 km2, making this event one of PdF's largest historical eruptions. The collapse changed the stability of the summit massif; as a result, during most of 2007, access to Dolomieu was prohibited due to the high risk of collapse of the crater walls.

OVPDLF reported that the eruption ceased on 1 May 2007 but that seismicity continued during 2-7 May at and below the summit, and also indicated a large number of landslides from the Dolomieu crater walls. Two earthquakes occurred on 4 May; one was M 3.8. Light tremor and several significant earthquakes persisted throughout May and were considered to be the result of a collapse at depth. GPS information showed a contracting of Dolomieu. The larger summit earthquakes, observed since the end of April, were considered to be precursors of such a movement. On 13 May a helicopter pilot reported that part of the edge of the crater had fallen.

There were no major events until 20 June 2007 when a large number of earthquakes were recorded, including several below sea level. Throughout the rest of 2007 and the first half of 2008, PdF remained relatively quiet.

Observations from 2008. Renewed seismicity was observed by OVPDLF/IPGP in early August 2008. General seismicity was high, with up to 100 seismic events per day and some magnitudes as high as M 3. Significant seismic events were recorded on 4 and 15 August. No deformation was observed on 4 August by the inclinometer or permanent GPS network; however a small seismic event on 15 August lasted a little more than 2.5 hours and deformation was detected at the top of Dolomieu. By 18 August seismicity had decreased and deformation was no longer detected.

Seismic activity beneath the summit was again detected on 31 August and deformation was detected at the top of Dolomieu. By 2 September seismicity had decreased. Seismicity during 8-9 September was characterized by hundreds of earthquakes. Permanent GPS measurements indicated inflation since August and a N-S widening of the Dolomieu crater by 6.5 cm.

On 12 September OVPDLF reported an eruption accompanied by small episodes of tremor. Although initial field observations confirmed increased degassing on the S-W Dolomieu crater and H2S in the air, no lava was found within the crater. Small amounts of SO2 were detected by the OVPDLF/IPGP NOVAC network on the Enclos Fouqué caldera rim. Aerial observation noted lava flows escaping from a crack in the W slope in the crater; a small lava lake formed at the bottom of the crater. On 13 September, 95 earthquakes occurred, including three of M 1.5-1.8 and nine of M 1-1.5 (others were smaller). The next day 94 earthquakes occurred at the summit.

More seismic events were detected during 15-16 September 2008 and numerous landslides occurred shortly thereafter, but these may have been facilitated by heavy rains. On those days, a total of 296 earthquakes were recorded. Seismicity and SO2 degassing continued.

An eruption took place during 21 September-2 October 2008. On 21 September, lava flows issued from the fissure about halfway up the W wall of Dolomieu crater. The lava flow ponded at the bottom. A strong concentration of SO2 was detected near the edge of the crater. On 22 September Pele's hair was found around the summit area and the lava flow rate decreased. No further earthquakes were observed after the beginning of the eruption and the volcanic activity was confined within the Dolomieu crater. The eruption of lava flows declined on 23 September.

During 24-30 September lava flows issued from the W crater wall continued to pond at the bottom of Dolomieu crater. Based on air photos acquired on 25 September, the lava flow was an estimated 180 m long by 100 m wide and about 30 m thick. The erupted volume was about 300,000 m3. On 26 September, lava fountaining from the fissure was no longer visible, but bubbling lava in the cone was observed. During that week tremor was relatively light and lava flows remained confined to the Dolomieu crater.

The eruption came to an end on 2 October and tremor decreased significantly. A total volume of lava emitted during this 10-day eruption was estimated at about 850,000 m3 based on analysis of aerial photographs. During the eruption only one small deflation episode was recorded.

On 20 October a seismic crisis began beneath the summit accompanied by weak deformation. Subsequent quiescence followed until 31 October when another seismic crisis was characterized by hundreds of earthquakes.

A new eruption began on 28 November 2008 from the vent halfway up the W wall of Dolomieu crater. The lava flows ponded at the bottom of the crater and covered about 50 percent of the 21 September lava flow. A small quantity of Pele's hair was deposited inside Bory crater.

On 14 December, the OVPDLF/IPGP recorded a strong seismic crisis under the volcano with several hundreds of earthquakes. However, substantial deformation was absent. An eruption commenced on 15 December from two fissures inside Dolomieu, halfway up the N and NE wall beneath "La Soufrière" and about 200 m below the crater rim. The eruption was sporadic and weak.

OVPDLF reported that during 22-28 December 2008 lava continued to issue at a high rate from an active vent on the N side of Dolomieu crater, beneath "La Soufrière" and about 200 m below the crater rim. Gas plumes often reduced visibility. On 24 December, a small cone formed at the vent and occasionally produced lava fountains that fed a small lava lake. GPS monitoring equipment indicated stable conditions. Throughout the eruption volcanic tremor was quite variable. Around this time, ten lava flows were visible on the inner flanks of the crater and a plume was visible. No fresh lava was visible at the cone on 29 December. The degassing was quite strong and sometimes Dolomieu was filled with bluish gas; a plume was visible on the webcam.

Observations from 2009. Tremor initially decreased in January, though by the 2nd it was increasing again. Tremor stabilized below levels seen on 15 December 2008, and remained at that level through at least 22 January, suggesting that eruptions continued.

References. Peltier, A., Staudacher, T., Bachélery, P., Cayol, V., in press, The April 2007 eruption and the Dolomieu crater collapse, two major events at Piton de la Fournaise (La Réunion Island, Indian Ocean): Journal of Volcanology and Geothermal Research (proof copy available online).

Peltier, A., Staudacher, T., and Bachélery, P., 2007, Constraints on magma transfers and structures involved in the 2003 actity at Piton de La Fournaise from displacement data: Journal Geophys. Res., v. 112, p. B03207, doi: 10.1029/2006JB004379.

Information Contacts: Laurent Michon and Patrick Bachélery, Laboratoire GéoSciences Réunion, Institut de Physique du Globe de Paris, Université de La Réunion, CNRS, UMR 7154-Géologie des Systèmes Volcaniques, La Réunion, France; Thomas Staudacher and Valérie Ferrazzini, Observatoire Volcanologique du Piton de la Fournaise (OVPDLF), Institut de Physique du Globe de Paris, 14 route nationale 3, 27 ème km, 97418 La Plaine des Cafres, La Réunion, France (URL: http://ovpf.univ-reunion.fr/); Joan Marti, Institute of Earth Sciences "Jaume Almera," Consejo Superior de Investigaciones Cientificas, Barcelona, Spain.

03/2010 (BGVN 35:03) Seismicity and eruptions January 2009 and November 2009-January 2010

Eruptions from Piton de la Fournaise resumed in September 2008 after more than 16 months of quiet (BGVN 34:02). Eruptive episodes inside Dolomeiu crater, as reported by the Observatoire Volcanologique du Piton de la Fournaise (OVPDLF), took during 21 September-2 October and on 28 November 2008, with a third that began on 15 December and continued into January 2009. This report presents observations from January 2009 through January 2010.

Eruptions during 21 September 2008-4 February 2009. Eruptive phases in September, November, and December 2008 were previously described (BGVN 34:02). OVPDLF reported that the episode that began on 14 December 2008 ended on 4 February 2009. During that eruption two vents were active; lava flowed to the bottom of Dolomieu crater through lava tubes and caused the crust over the pooled area to rise. Some incandescence was noted at night and at dawn. Eruption tremor was irregular until 1 January, when it suddenly stopped. Tremor gradually rose over the next few days, but to a relatively low level, where it remained steady until slowly dropping again in early February (figure 79). Lava flows from this eruption covered an area of approximately 420 x 220 m, with a thickness of 75 m (figure 80).

Figure 79. Tremor at Piton de la Fournaise, 14 December 2008-5 February 2009. Courtesy of OVPDLF.
Figure 80. Cumulative lava flows in Dolomieu crater at Piton de la Fournaise during the September 2008-February 2009 eruption. Flows covered 420 x 220 m to a depth of 75 m. Courtesy of OVPDLF.

Activity during October 2009-January 2010. The OVPDLF reported three eruptions from the summit region at the Dolomieu crater's W wall adjacent to Bory crater between November 2009 and January 2010. The flows traveled to the E down the steep cliff toward the crater floor. These eruptions began on 5 November 2009, lasting about two days; on 14 December 2009, lasting 6 hours; and on 2 January 2010, lasting 10 days.

During 5-13 October 2009, OVPDLF reported increased seismicity (figure 81). Seismicity from 14 to 17 October indicated deformation on the N side of, and rockfalls within, the Dolomieu crater. On 18 October another seismic crisis was noted along with deformation on the N and S sides of the Dolomieu crater. Aerial observations on 19 October revealed a small new fumarole in the crater. Unspecified changes in the chemical composition of the gases were also noted. On 20 October rockfalls occured in greater number and longer duration than in previous days.

Figure 81. A graph showing the number of volcano-tectonic earthquakes/day registered between 1 July 2009 and 26 January 2010 at Piton de la Fournaise. Horizontal bars indicate eruptions. Courtesy OVPDLF.

On 4 November 2009 a magnitude 3 earthquake at 0604 was felt by some residents of the southern part of the island. Such a magnitude is uncommon at this volcano. Seismologists at the Observatory located the earthquake at 750 m below sea level, under the southwestern edge of the Dolomieu crater. Later that day, 167 earthquakes of lesser magnitude followed. The focal depths rose to ~ 1 km above sea level with epicenters below the summit.

OVPDLF reported that 30 minutes after an intense seismic event on 5 November, a tremor signal characteristic of the beginning of an eruption occurred, and a vent opened inside the southern part of the Dolomieu crater. Within another 30 minutes, a fissure on the upper SE flank propagated E, and a second fissure opened on the E flank.

Lava fountains ~ 20 m high and flows were emitted from both fissures. The glowing lava was visible from the edge of the Enclos Fouqué and from the road in the Grand Brulé. Beginning around 1500, there was a gradual decrease in the intensity of the eruption. At 0645 on 6 November, a reconnaissance was conducted by a helicopter supplied by the National Gendarmerie, which confirmed that two fissures were open in the S side, S and E of the Dolomieu summit crater. Each emitted a lava flow descending to ~ 1,970 m elevation. As of 0730 that day, the lava ceased flowing, with a gradual decrease in the intensity of the eruption tremor.

At 1730 on 14 December a seismic event preceded a rise in summit deformation (8 cm horizontal). Eruptive tremor began at 1830, and an eruption began at 1845. A system of sub-parallel fissures along the summit of Dolomieu crater fed lava flows on the S slope of the volcano, inside the Enclos Fouqué. A second fissure system opened on the E flank of the Dolomieu summit crater at 2025, and lava flows advanced down the eastern slope. This eruption ended at 0040 after a gradual decrease in magma supply. On 15 December, a visible degassing in the S and SE fissures was associated with low-intensity eruptive tremor. All of the lava flows were confined to high portions of the S and SE slopes.

Fissure-fed fountaining sent lava flows down the S flank on 14 December 2009. Another seismic event on 29 December was characterized by numerous earthquakes up to M 3 in the area W and NW of Dolomieu crater at depths of 1.1-2.2 km below the summit. Deformation was also detected. OVPDLF reported decreased seismicity and fewer landslides within Dolomieu crater on 30 and 31 December.

On 2 January 2010 a fissure eruption near the top of the W crater rim (figure 82) was preceded by a seismic event and another 3 cm of horizontal deformation. Lava fountains rose a few tens of meters high and sent lava flows into Dolomieu crater, and ash and gas plumes rose above Piton de la Fournaise. Large landslides also occurred in Bory crater (W). During 2-3 January, seismicity and the number of landslides decreased. A series of ash plumes was noted through 12 January.

Figure 82. Dolomieu crater on 2 January from its W rim showing lava flows and fountains. The dense gray plume was attributed to collapse along the steep crater wall. Courtesy of OVPDLF.

As of 4 January, the lava flows covered about 80% of the crater floor. Lava fountaining was still visible during 5-7 January and continued to erupt from a vent along a fissure high on the SW Dolomieu crater wall. The vent produced lava fountains and flows that pooled in the bottom of the crater. On 7 January the vent closed, but the previously erupted lava continued to flow for the next few days (figure 83). Seismicity decreased on 12 January and only minor gas emissions persisted. Figure 82 shows the lava flow along the axis where extensive glowing flows were visible. Some flows around this time were fed by lava tubes.

Figure 83. A photo taken on the morning of 7 January 2010 of the lava vent flows from the W wall adjacent to Bory crater at Piton de la Fournaise. Courtesy of Undervol, OVPDLF.

Information Contacts: Laurent Michon and Patrick Bachélery, Laboratoire GéoSciences Réunion, Institut de Physique du Globe de Paris, Université de La Réunion, CNRS, UMR 7154-Géologie des Systèmes Volcaniques, La Réunion, France; Guillaume Levieux, Thomas Staudacher, and Valérie Ferrazzini, Observatoire Volcanologique du Piton de la Fournaise (OVPDLF), Institut de Physique du Globe de Paris, 14 route nationale 3, 27ème km, 97418 La Plaine des Cafres, La Réunion, France (URL: http://ovpf.univ-reunion.fr/).

03/2012 (BGVN 37:03) Increased seismicity and eruption during late 2010

Our last Bulletin report (BGVN 35:03) covered eruptive activity through the last eruptive episode, which ended 12 January 2010.

Beginning 14 August and through 10 September 2010, the Observatoire Volcanologique du Piton de la Fournaise (OVPDLF) recorded a slow but steady increase in the number and magnitude of earthquakes from Piton de la Fournaise. Inflation of the summit area began in late August. The following report is based on data received from OVPDLF. It discusses eruptions and related behavior as late as 10 December 2010.

On 13 September 2010, localized deformation W of the Dolomieu crater and a small number of landslides in the crater was observed. On 20 September instruments recorded a significant increase in the number of earthquakes located at the W and S of the Dolomieu crater, although their average magnitude was low.

On 24 September, OVPDLF reported the possibility of an impending eruption. During the night, a seismic crisis began with a series of several tens of earthquakes localized under the Dolomieu crater, which was associated with inflation (approximately 3 cm), especially close to the summit. The most significant deformations were measured on the rim and the N and S sides of the volcano, indicating a shallow magma body was distributed directly below the Dolomieu crater. After decreasing on 27 September, seismicity rose again by 29 September. Earthquakes were located at the base of the volcano, and inflation was noted particularly in the E. A significant number of landslides were detected in the crater. The Alert level remained at 1 (“probable or imminent eruption”).

Beginning 7 October 2010, there was a steady increase in the number and magnitude of volcano-tectonic (VT) earthquakes. During 10-11 October the summit area inflated 3-7 cm, and an increase in the number of landslides in the crater was detected. The Alert level remained at 1.

Increased seismicity was again recorded on 14 October 2010, with a new seismic crisis of more than several hundred earthquakes. During this phase, significant ground deformation occurred near the summit, which generated numerous rockfalls inside the Dolomieu crater. At 1411, the seismicity moved toward the SE part of the volcano (Château Fort), and at 1910 an eruption began within the Enclos Fouqué, about 1.5 km SE of the Dolomieu crater rim. Lava fountaining occurred from four vents along a fissure. The Alert level was raised to 2 (“eruption in progress in the Fouqué caldera”).

Eruptive activity continued on 15-16 October 2010, developing along a fissure. This eruption included low lava fountains and fed a lava flow moving to the ESE. Lava issued from an area close to the old Château Fort crater at the base of the SE flank of Dolomieu crater and remained within the Enclos Fouqué. Four small cones were active along the eruptive fissure; lava fountaining occured from three of them. A lava flow moved slowly about 1.6 km to the E and SE and approached the break in slope at the Grandes pentes. OVPDLF measured lava temperatures of ~1,100°C.

On 17 October 2010 explosions and degassing accompanied lava emissions. These explosions and degassing decreased on 18 October. The volcanic tremor also decreased to one-seventh compared to the beginning of the eruption. The number of VT events remained low (7/day); the strongest event occurred at 2323, a M 1.4 earthquake localized at about 1,600 m depth under the Bory summit crater. The base and the summit of the volcano remained in inflation. Preliminary estimation of the lava volume erupted was 600,000 m3.

During 19-21 October consistent eruptive activity continued, with weak emissions and small lava fountains at the main eruptive vents located along the eruptive fissure. Explosive activity and degassing decreased, and tremor remained stable. Lava flows extended ESE to ~2 km. Gas emissions decreased, but concentrated to the S and W of the fissure.

On 22 October 2010 eruptions continued, located close to the Château Fort area, in the southern portion of the Enclos Fouqué. During 22-26 October lava fountains and gas emissions originated from one vent, and lava traveled ESE. Gas emissions decreased significantly. At this point, only one cone was active and only a few lava fountains were observed. Volcanic tremor was stable. No earthquakes had been reported since the previous day. GPS ground deformation showed a weak deflation under the volcano.

A sudden increase in activity and tremor began on 27 October 2010 and continued on 28 October. On 29 October, observation made during a flight disclosed that a part of summit cone 3 (the only active cone) had collapsed. Some lava ejecta and gas emissions occurred from this cone, which also contained a small active lava pond. Lava from this cone fed a small, slow moving lava flow. This new lava field remained upstream of the cone named Gros Benard. On 31 October, OVPDLF reported that the eruption had ended.

On 9 December 2010, following a seismic crisis and inflation, a new eruption began from an eruptive fissure oriented N-S, just above the Mi-Côte peak, at ~2,500 m elevation, characterized by lava fountaining and two lava flows. Many small landslides occurred in the Dolomieu crater. Later that day lava flows from two fissures on the N flank of Piton de la Fournaise, ~1 km NW of the Dolomieu crater rim, traveled about 1.5 km N and NW. On 10 December 2010, seismicity and deformation measurements indicated that eruption of lava had stopped.

Information Contacts: Laurent Michon and Patrick Bachélery, Laboratoire GéoSciences Réunion, Institut de Physique du Globe de Paris, Université de La Réunion, CNRS, UMR 7154-Géologie des Systèmes Volcaniques, La Réunion, France; Guillaume Levieux, and Thomas Staudacher, and Valérie Ferrazzini, Observatoire Volcanologique du Piton de la Fournaise (OVPDLF), Institut de Physique du Globe de Paris, 14 route nationale 3, 27ème km, 97418 La Plaine des Cafres, La Réunion, France (URL: http://ovpf.univ-reunion.fr/).

The massive Piton de la Fournaise basaltic shield volcano on the French island of Réunion in the western Indian Ocean is one of the world's most active volcanoes. Much of its more than 530,000-year history overlapped with eruptions of the deeply dissected Piton des Neiges shield volcano to the NW. Three calderas formed at about 250,000, 65,000, and less than 5000 years ago by progressive eastward slumping of the volcano. Numerous pyroclastic cones dot the floor of the calderas and their outer flanks. Most historical eruptions have originated from the summit and flanks of Dolomieu, a 400-m-high lava shield that has grown within the youngest caldera, which is 8 km wide and breached to below sea level on the eastern side. More than 150 eruptions, most of which have produced fluid basaltic lava flows, have occurred since the 17th century. Only six eruptions, in 1708, 1774, 1776, 1800, 1977, and 1986, have originated from fissures on the outer flanks of the caldera. The Piton de la Fournaise Volcano Observatory, one of several operated by the Institut de Physique du Globe de Paris, monitors this very active volcano.

Summary of Holocene eruption dates and Volcanic Explosivity Indices (VEI).

Start Date Stop Date Eruption Certainty VEI Evidence Activity Area or Unit
2014 Jun 21 2014 Jun 21 (?) Confirmed 0 Historical Observations Enclos Fouqué
2010 Oct 14 2010 Dec 10 Confirmed 1 Historical Observations 2.5 km SE and 1 km NW of Dolomieu
2009 Nov 5 2010 Jan 12 Confirmed 1 Historical Observations Dolomieu crater and east flank
2008 Sep 21 2009 Feb 4 Confirmed 1 Historical Observations Dolomieu crater
2006 Jul 20 2007 May 1 Confirmed 1 Historical Observations Dolomieu, S, E, and SE flanks
2005 Oct 4 2006 Jan 18 Confirmed 0 Historical Observations Dolomieu, N and NE flanks
2005 Feb 17 2005 Feb 26 Confirmed 0 Historical Observations North side of caldera (1600, 1200, & 450 m)
2004 May 2 2004 Oct 16 Confirmed 0 Historical Observations SSW of Bory, Dolomieu and east flank
2003 May 30 2004 Jan 10 Confirmed 1 Historical Observations Dolomieu, Bory, N, NW, and SSW flanks
2002 Nov 16 2002 Dec 3 Confirmed 2 Historical Observations East flank of Dolomieu (1850-1540 m)
2002 Jan 5 2002 Jan 16 Confirmed 1 Historical Observations NE part of l'Enclos Fouqué caldera
2001 Jun 11 2001 Jul 7 Confirmed 1 Historical Observations ESE flank (2500 m), East flank (1800-2000 m)
2001 Mar 27 2001 Apr 4 Confirmed 1 Historical Observations South flank (below Dolomieu at ~2500 m)
2000 Jun 23 2000 Nov 13 Confirmed 1 Historical Observations SE flank (2100-1800 m), E flank (2260-2000 m)
2000 Feb 14 2000 Mar 4 Confirmed 1 Historical Observations North flank of Dolomieu (2490-2250 m)
1999 Jul 19 1999 Oct 23 Confirmed 1 Historical Observations Dolomieu, E (2500-2100) &S flanks (1900 m)
1998 Mar 9 1998 Sep 20 (?) Confirmed 1 Historical Observations N and WSW of Dolomieu, outer N flank
1992 Aug 27 1992 Sep 23 Confirmed 1 Historical Observations Dolomieu and upper SE flank
1991 Jul 19 1991 Jul 20 Confirmed 0 Historical Observations Dolomieu and upper east flank
1990 Jan 18 1990 May 8 Confirmed 0 Historical Observations Dolomieu and SE flank
1985 Jun 14 1988 Dec 29 Confirmed 1 Historical Observations Dolomieu and flanks, SE rift zone
1983 Dec 4 1984 Feb 18 Confirmed 2 Historical Observations SSW flank of Dolomieu (2110-2300 m)
1981 Feb 3 1981 May 5 Confirmed 2 Historical Observations Bory, SW, N & NE of Dolomieu
1979 May 28 1979 Jul 14 Confirmed 1 Historical Observations SE, SW and N flanks, Dolomieu & Bory
1977 Oct 24 1977 Nov 17 Confirmed 1 Historical Observations ENE flank (2050-2200 m, 1850-1920 m)
1977 Mar 24 1977 Apr 16 Confirmed 0 Historical Observations NE and SE of Dolomieu, NE rift zone
1976 Nov 2 1976 Nov 4 (?) Confirmed 1 Historical Observations North of Dolomieu (2250-2330 m)
1975 Nov 4 1976 Apr 6 Confirmed 1 Historical Observations Dolomieu and SE flank (1320-2350 m)
1973 May 10 1973 Sep 5 (?) Confirmed 2 Historical Observations Dolomieu (SSW wall)
1972 Jun 9 (?) 1973 Jan 16 (?) Confirmed 2 Historical Observations South, ENE, north and SE of Dolomieu
1966 Mar 15 1966 May 15 Confirmed 2 Historical Observations SE flank (Cratere Maillard, 2400 m)
1964 Dec 21 1965 Feb 15 Confirmed 2 Historical Observations East flank (1930 m)
1964 Apr 30 1964 May 8 Confirmed 2 Historical Observations Dolomieu, upper east and NE flanks
1963 Nov 7 1963 Nov 21 Confirmed 2 Historical Observations Dolomieu, upper east flank (2410 m)
1961 Apr 5 1961 Apr 25 Confirmed 0 Historical Observations NE flank (east of Cratère Picard)
1960 Jan 11 1960 Mar 10 Confirmed 2 Historical Observations Bory, south flank (2030 m)
1959 Mar 11 1959 Aug 6 Confirmed 2 Historical Observations Bory
1958 May 30 1958 Sep 20 Confirmed 2 Historical Observations Dolomieu
1957 Sep 2 1957 Nov 16 Confirmed 2 Historical Observations Bory, N of Bory, NE of Dolomieu
1955 Jul 6 1957 Mar 16 Confirmed 2 Historical Observations Dolomieu, Bory, S, SE & ESE flanks
1954 Jan 1954 Dec Confirmed   Historical Observations
1953 Mar 13 1953 Jul 8 Confirmed 2 Historical Observations South, NW & N flanks, Dolomieu, Bory
1952 May 19 1952 Jul 20 Confirmed 2 Historical Observations NE flank near north rim (1500 m)
1951 Sep 10 1951 Sep 20 Confirmed 1 Historical Observations
[ 1951 Jun ] [ Unknown ] Uncertain 0   North part of Grand Brule
1950 Aug 30 1950 Sep 5 Confirmed 2 Historical Observations SE of Bory
1950 Feb 25 1950 Apr 2 Confirmed 2 Historical Observations South flank (2080 m)
[ 1949 Oct ] [ Unknown ] Uncertain 2  
1948 Feb 14 1948 Mar 8 Confirmed 2 Historical Observations South flank (le Chateau Fort)
1947 (?) Unknown Confirmed 2 Historical Observations Dolomieu, Grand Brule
1946 Jun 18 1946 Jul 5 Confirmed 2 Historical Observations Dolomieu crater and upper flanks
1945 Apr 15 1945 May 6 Confirmed 2 Historical Observations SE flank near Nez Coupe du Tremblet
1944 Apr 11 1944 May 1 Confirmed 2 Historical Observations
1943 Mar 30 (?) 1943 May 26 ± 5 days Confirmed 2 Historical Observations SE of Dolomieu, lower Grandes Pentes
1942 Oct 5 1942 Oct 25 Confirmed 2 Historical Observations Bory, rim of Dolomieu
1941 (?) Unknown Confirmed 1 Historical Observations
1938 Dec 7 1939 Jan 15 Confirmed 2 Historical Observations ESE and SW flanks, Dolomieu
1938 Jul 25 1938 Jul 29 Confirmed 1 Historical Observations
1937 Aug 13 1937 Nov 25 Confirmed 2 Historical Observations Bory, flanks of Bory and Dolomieu
1936 Sep Unknown Confirmed 0 Historical Observations Near 1933 crater
1935 (?) Unknown Confirmed 2 Historical Observations
1933 Jun 7 1934 Apr 1 Confirmed 2 Historical Observations Dolomieu, upper and SE flanks
1932 Nov 1932 Nov Confirmed   Historical Observations
1931 Jan 22 1931 Aug 26 ± 5 days Confirmed 2 Historical Observations Summit, NE flank (Cratère Haug)
1930 May 23 1930 May 24 Confirmed 0 Historical Observations
1929 Dec 23 1929 Dec 31 Confirmed 2 Historical Observations
1926 Sep 18 1927 Jun 15 Confirmed 2 Historical Observations North flank
1925 Dec 30 1926 Apr 20 Confirmed 2 Historical Observations
1924 Sep 3 1924 Sep 13 Confirmed 2 Historical Observations
1924 May 19 1924 May 23 (in or after) Confirmed 0 Historical Observations
1921 Nov 27 1921 Dec 3 Confirmed 2 Historical Observations
1920 Jun 28 1920 Oct 18 Confirmed 0 Historical Observations
1917 Apr 29 1917 Apr 29 Confirmed 0 Historical Observations NE flank (above Piton de Crac)
1915 Jul 22 1915 Nov 21 Confirmed 2 Historical Observations Summit, N and NE of Crater Velain
1913 Jul 10 1913 Aug 3 Confirmed 2 Historical Observations
1910 Nov 16 1910 Dec 12 Confirmed 2 Historical Observations
1909 Apr Unknown Confirmed 2 Historical Observations East of Cratère Faujas
[ 1908 ] [ Unknown ] Uncertain 0  
1907 Nov 29 1907 Dec 5 ± 4 days Confirmed 0 Historical Observations
1905 Feb 15 1905 Feb 16 Confirmed 2 Historical Observations
1904 Aug 19 1904 Oct 17 Confirmed 2 Historical Observations NE flank (above Piton de Crac)
1903 (?) Unknown Confirmed 0 Historical Observations
1902 Aug 13 1902 Aug 18 Confirmed 2 Historical Observations
1901 Jul 4 1901 Jul 6 Confirmed 2 Historical Observations NE flank (above Piton de Crac)
1901 Feb 21 1901 Feb 25 Confirmed 2 Historical Observations East of Dolomieu
1900 May 11 1900 May 30 Confirmed 0 Historical Observations East of Dolomieu
1899 Feb 13 1899 Jul 18 (in or after) Confirmed 2 Historical Observations
1898 Nov 26 Unknown Confirmed 2 Historical Observations
1898 Jan 14 1898 Jan 20 Confirmed 2 Historical Observations
1897 Jan 5 ± 4 days 1897 Jan 24 Confirmed 0 Historical Observations
1894 Aug Unknown Confirmed 2 Historical Observations
1890 Feb 1891 Feb 4 Confirmed 2 Historical Observations Summit, Grandes Pentes
1889 Jun 1889 Aug 11 (in or after) Confirmed 2 Historical Observations Grandes Pentes and summit
1884 Feb 4 1884 Feb 5 Confirmed 0 Historical Observations
[ 1882 ] [ Unknown ] Uncertain 0  
1878 Mar 14 1878 Mar 30 Confirmed 0 Historical Observations
1876 Dec 11 1876 Dec 11 (?) Confirmed   Historical Observations
1875 Nov 26 1875 Dec 11 (?) Confirmed 0 Historical Observations
1874 Jun 29 1874 Nov 7 (in or after) Confirmed 2 Historical Observations
1874 Feb 1 ± 30 days Unknown Confirmed   Historical Observations
[ 1872 Feb 1 ± 30 days ] [ Unknown ] Uncertain 0  
1871 Jun 21 1871 Jul 5 Confirmed 0 Historical Observations
[ 1870 Feb 1 ± 30 days ] [ Unknown ] Uncertain 0  
1869 (?) Unknown Confirmed 2 Historical Observations
1868 Mar Unknown Confirmed 0 Historical Observations
1865 Feb 5 1865 Feb 10 Confirmed 2 Historical Observations
1863 Dec 20 1864 Jan 29 Confirmed 0 Historical Observations
1861 Mar 19 1861 Mar 19 Confirmed 2 Historical Observations Brulant
1860 Jan 22 1860 Mar 20 Confirmed 2 Historical Observations Dolomieu and l'Enclos
1859 May 8 1859 May 23 (in or after) Confirmed 2 Historical Observations
1858 Nov 3 1859 Jan Confirmed 2 Historical Observations
1852 Unknown Confirmed 0 Historical Observations Brulant
1851 Unknown Confirmed 0 Historical Observations Brulant, l'Enclos Velain
1850 Nov 3 1850 Nov 12 Confirmed 0 Historical Observations
1849 Unknown Confirmed 0 Historical Observations
1848 Unknown Confirmed 0 Historical Observations
1847 Unknown Confirmed 0 Historical Observations
1846 Unknown Confirmed 0 Historical Observations
1845 Unknown Confirmed 0 Historical Observations
1844 Dec Unknown Confirmed 2 Historical Observations
1844 Mar 19 1844 May 11 Confirmed 2 Historical Observations Summit and Piton de Crac
1843 Unknown Confirmed 0 Historical Observations
1842 Apr Unknown Confirmed 0 Historical Observations
1832 Mar Unknown Confirmed 0 Historical Observations L'Enclos and NE rift zone
1830 Oct Unknown Confirmed 0 Historical Observations Cratere Faujas
1824 Dec Unknown Confirmed 0 Historical Observations
1824 Feb Unknown Confirmed 0 Historical Observations
1821 Feb 27 1821 Apr 10 Confirmed 2 Historical Observations
1820 Jan 1820 Feb Confirmed 2 Historical Observations NW rift zone
1817 Jan 1817 Apr Confirmed 0 Historical Observations
1816 Dec 15 Unknown Confirmed 0 Historical Observations
1815 Aug 15 1815 Aug 16 Confirmed 2 Historical Observations Summit and Plaine des Osmondes
1815 Jan 21 1815 Jan 27 Confirmed 2 Historical Observations
1814 Sep 10 1814 Oct 13 Confirmed 2 Historical Observations
1813 Sep 26 1813 Nov 26 Confirmed 2 Historical Observations
1812 Aug 5 ± 4 days 1812 Dec Confirmed 2 Historical Observations Summit and above Piton de Crac
1810 Nov 20 1810 Nov 28 Confirmed 2 Historical Observations
1809 Jul 17 1809 Aug 8 Confirmed 2 Historical Observations
1807 Mar 23 1807 Jun 13 Confirmed 2 Historical Observations
1802 Dec Unknown Confirmed 2 Historical Observations
1801 Oct 27 1802 Apr 28 ± 7 days Confirmed 2 Historical Observations Mammelon Central
1800 Nov 2 1800 Nov 8 Confirmed 0 Historical Observations SE rift zone
1797 (?) Unknown Confirmed 0 Historical Observations
1795 Unknown Confirmed   Historical Observations
1794 Jan 1794 Jan Confirmed 0 Historical Observations
1792 Dec 19 (?) Unknown Confirmed 0 Historical Observations
1791 Jun 5 ± 4 days 1791 Jul 27 (?) Confirmed 2 Historical Observations Dolomieu, Mamelon Central ?
1789 Jun 1789 Jul Confirmed 2 Historical Observations East side of summit cone and Bory crater
1787 Jun 14 1787 Aug 1 Confirmed 2 Historical Observations Bory
1786 Jun 5 (?) 1786 Aug 4 (in or after) Confirmed 2 Historical Observations
1784 1785 Confirmed 2 Historical Observations
1776 Unknown Confirmed 0 Historical Observations SE rift zone (Piton Takamaka)
1775 Unknown Confirmed 2 Historical Observations East side of summit cone
1774 Unknown Confirmed 0 Historical Observations SE rift zone
1772 Nov 18 Unknown Confirmed 2 Historical Observations
1772 Feb Unknown Confirmed 2 Historical Observations
1771 Unknown Confirmed   Historical Observations
1768 Unknown Confirmed 2 Historical Observations Formica Leo
1766 Mar 1766 May 26 ± 5 days Confirmed 2 Historical Observations
1760 Dec 15 1760 Dec 29 Confirmed 2 Historical Observations East flank
1759 Unknown Confirmed   Historical Observations
1753 Unknown Confirmed 2 Historical Observations
1751 Jun 1751 Jun Confirmed 2 Historical Observations
1734 Dec 1734 Dec Confirmed 2 Historical Observations
1734 Jan 1 1734 Mar 6 Confirmed 2 Historical Observations
1733 (?) Unknown Confirmed 0 Historical Observations L'Enclos and NE rift zone
1721 Jun Unknown Confirmed 2 Historical Observations
1709 Unknown Confirmed 2 Historical Observations
1708 Apr 1708 Apr Confirmed 0 Historical Observations NE rift zone
1703 (in or before) 1705 Confirmed 0 Historical Observations
1672 Unknown Confirmed 2 Historical Observations
1671 Unknown Confirmed 2 Historical Observations
1669 Unknown Confirmed 2 Historical Observations
1649 Unknown Confirmed 2 Historical Observations
1640 Unknown Confirmed 2 Historical Observations
1600 (?) Unknown Confirmed 0 Radiocarbon (corrected) S rift zone (Piton Taye Poule)
1440 (?) Unknown Confirmed 0 Radiocarbon (corrected) Upper NW flank (Petit Cratère)
1340 (?) Unknown Confirmed 0 Radiocarbon (corrected) South rift zone (Brulé du Baril)
0960 (?) Unknown Confirmed 0 Radiocarbon (corrected) Upper W flank (Piton Chisny)
0600 (?) Unknown Confirmed 0 Radiocarbon (corrected) Upper NW flank (Piton Gîte)
0460 (?) Unknown Confirmed 0 Radiocarbon (uncorrected)
0120 (?) Unknown Confirmed 0 Radiocarbon (corrected) Upper NW flank (Cratère Commerson)
1790 BCE ± 100 years Unknown Confirmed   Radiocarbon (uncorrected)
2700 BCE (?) Unknown Confirmed 5 Radiocarbon (corrected) Bellecombe Ash Member
2800 BCE ± 150 years Unknown Confirmed   Radiocarbon (uncorrected)

This compilation of synonyms and subsidiary features may not be comprehensive. Features are organized into four major categories: Cones, Craters, Domes, and Thermal Features. Synonyms of features appear indented below the primary name. In some cases additional feature type, elevation, or location details are provided.



Synonyms
Reunion, Volcan de la | Grand Pays Brule | Grandes Pentes


Cones
Feature Name Feature Type Elevation Latitude Longitude
Balmann, Piton de Cinder cone
Bredes, Piton Cinder cone
Cabris, Piton des Cinder cone
Calomets, Piton Cinder cone
Caverne Pomme de Terre, Piton Cinder cone
Ceille, Piton Cinder cone
Chat, Piton de Cinder cone
Cheli Mine, Piton Cinder cone
Chisny, Piton Cinder cone
Citrons Galets, Piton Cinder cone
Cochons, Piton des Cinder cone
Coco, Piton de Cinder cone
Commerson, Cratere Cinder cone
Crac, Piton de Cinder cone
D'ango, Piton Cinder cone
Durandal Cinder cone
Eliane Cone Submarine cone
Fourche, Piton de Cinder cone
Glace, Piton Cinder cone
Grands Bois, Piton des Cinder cone
Gros Piton Cinder cone
Guanyin, Piton Cinder cone
Gueuie Ronde, Piton Cinder cone
Hauy, Piton Cinder cone
Hubert, Piton Cinder cone
Lacroix, Piton Cinder cone
L'Eau, Piton de Cinder cone
L'Liet, Piton de Cinder cone
Moka, Piton Cinder cone
Morgabim, Piton Cinder cone
Moustabismen, Piton de Cinder cone
Nelson, Piton Cinder cone
Parvedi, Piton Cinder cone
Pas des Sables, Puy Cinder cone
Raymond, Puys Cinder cone
Rond, Piton Cinder cone
Rouge, Piton Cinder cone
Sauvetage, Piton Cinder cone
Sonne Cone Cone
Ste-Rose, Piton Cinder cone
Takamaka, Piton Cinder cone
Tangues, Piton Cinder cone
Tourkal, Piton Cinder cone
Trois Tetes, Piton Cinder cone
Zoe Cinder cone


Craters
Feature Name Feature Type Elevation Latitude Longitude
Alfred Picard, Cratere Crater
Bonnet, Le Crater
Bory Crater
Brulant Crater
Brulé du Baril Crater
Cassien, Cratere Crater
Caubet, Cratere Crater
Chateau Fort, Le Crater
Cordemoy, Cratere de Crater
Deuxieme Formica Leo Crater
Dolomieu Crater
Ducrot Crater
Faujas, Cratere Crater
Fontaipe, Cratere Crater
Formica Leo Crater
Fred Hudson Crater Crater
Gerente, Le Crater
Gros Benard, Le Crater
Haug, Cratere Crater
Hugolin, Crateres Crater
Jean Crater
Jeremine Crater
Kapor, Piton Fissure vent
Langfois, Le Crater
L'Enclos Fouqué Caldera
Magne, Cratere Crater
Maillard Crater
Marco, Cratere Crater
Maurice and Katia Krafft Crater Crater
Nouveau Crater
Passage, Cratere du Crater
Perfait, Piton Crater
Quatre Gueules Crater
Sery, Cratere Crater
Signal de L'Enclos Crater
Taye Poule, Piton Crater
Thierry Crater
Velain
    Enclos Velain
Crater
Villele, Cratere de Crater
von Drasche, Cratere Crater


Domes
Feature Name Feature Type Elevation Latitude Longitude
Mamelon Central Former dome
The massive Piton de la Fournaise on the island of Réunion is one of the world's most active volcanoes. It is seen here in 1977 with a fresh black lava flow descending the outer NE flank of the shield volcano to the sea. An unvegetated summit lava shield (upper left) was constructed within an 8-km-wide caldera that is breached to the sea. Its sloping northern rim is marked by the diagonal vegetation line at the left. More than 150 eruptions have occurred since the 17th century, mostly from vents within the caldera.

Copyrighted photo by Katia and Maurice Krafft, 1977 (published in SEAN Bulletin, 1977).

The following references have all been used during the compilation of data for this volcano, it is not a comprehensive bibliography. Discussion of another volcano or eruption (sometimes far from the one that is the subject of the manuscript) may produce a citation that is not at all apparent from the title.

Abchir A M, Semet M P, Boudon G, Ildefonse P, Bachelery P, Clocchiatti R, 1998. Huge hydrothermal explosive activity on Piton de la Fournaise, Reunion Island: the Bellecombe Member, 2700 BC. In: Casale R, Fytikas M, Sigvaldasson G, Vougioukalakis G (eds), The European laboratory volcanoes, Proc 2nd Workshop, Santorini, Greece 2-4 May 1996, European Comm, p 447-455.

Albarede F, Tamagnan V, 1988. Modelling the recent geochemical evolution of the Piton de la Fournaise Volcano, Reunion Island, 1931-1986. J Petr, 29: 997-1030.

Battaglia J, Aki K, Ferrazzini V, 2005. Location of tremor sources and estimation of lava output using tremor source amplitude on the Piton de la Fournaise volcano 2. Estimation of lava output. J Volc Geotherm Res, 147: 291-308.

Carter A, van Wyk de Vries B, Kelfoun K, Bachelery P, Briole P, 2007. Pits, rifts and slumps: the summit structure of Piton de la Fournaise. Bull Volc, 69: 741-756.

Coppola D, Staudacher Th, Cigolini C, 2005. The May-July 2003 eruption at Piton de la Fournaise (La Reunion): volume, effusion rates, and emplacement mechanisms inferred from thermal imaging and Global Positioning System (GPS) survey. In: Manga M, Ventura G (eds) Kinematics and dynamics of lava flows, {Geol Soc Amer Spec Pap}, 396: 103-124.

Duffield W A, Stieltjes L, Varet J, 1982. Huge landslide blocks in the growth of Piton de la Fournaise, Reunion, and Kilauea volcano, Hawaii. J Volc Geotherm Res, 12: 147-160.

Fretzdorff S, Paterne M, Stoffers P, Ivanova E, 2000. Explosive activity of the Reunion Island volcanoes through the past 260,000 years as recorded in deep-sea sediments. Bull Volc, 62: 266-277.

Gillot P-Y, Nativel P, 1989. Eruptive history of the Piton de la Fournaise volcano, Reunion Island, Indian Ocean. J Volc Geotherm Res, 36: 53-65.

Lenat J-F, Boivin P, Deniel C, Gillot P-Y, Bachelery P, Fournaise 2 Team, 2009. Age and nature of deposits on the submarine flanks of Piton de la Fournaise (Reunion Island). J Volc Geotherm Res, 184: 199-207.

Lenat J-F, Vincent P, Bachelery P, 1989. The off-shore continuation of an active basaltic volcano: Piton de la Fournaise (Reunion Island, Indian Ocean); structural and geomorphological interpretation from SEABEAM mapping. J Volc Geotherm Res, 36: 1-36.

Longpre M-A, Staudacher T, Stix J, 2007. The November 2002 eruption at Piton de la Fournaise volcano, La Reunion Island: ground deformation, seismicity, and pit crater collapse. Bull Volc, 69: 511-525.

Malengreau B, Lenat J-F, Froger J-L, 1999. Structure of Reunion Island (Indian Ocean) inferred from the interpretation of gravity anomalies. J Volc Geotherm Res, 88: 131-146.

Michon L, Cayol V, Letourneur L, Peltier A, Villeneuve N, Staudache T, 2009. Edifice growth, deformation and rift zone development in basaltic setting: Insights from Piton de la Fournaise shield volcano (Reunion Island). J Volc Geotherm Res, 184: 14-30.

Michon L, Staudacher T, Ferrazzini V, Bachelery P, Marti J, 2007. April 2007 collapse of Piton de la Fournaise: a new example of caldera formation. Geophys Res Lett, 34: L21301, doi:10.1029/2007GL031248.

Montaggioni L, Nativel P, Billard G, 1972. L'activite actuelle du Piton de la Fournaise (Ile de la Reunion, Ocean Indien). CR Acad Sci Paris, Ser-D, 275: 2615-2618.

Neumann van Padang M, 1963. Arabia and the Indian Ocean. Catalog of Active Volcanoes of the World and Solfatara Fields, Rome: IAVCEI, 16: 1-64.

Oehler J-F, Labazuy P, Lenat J-F, 2004. Recurrence of major flank landslides during the last 2-Ma history of Reunion Island. Bull Volc, 66: 585-598.

Oehler J-F, Lenat J-F, Labazuy P, 2008. Growth and collapse of the Reunion Island volcanoes. Bull Volc, 70: 717-742.

Peltier A, Bachelery P, Staudacher T, 2009. Magma transport and storage at Piton de La Fournaise (La Reunion) between 1972 and 2007: a review of geophysical and geochemical data. J Volc Geotherm Res, 184: 93-108.

Sigmarsson O, Condomines M, Bachelery P, 2005. Magma residence time beneath the Piton de la Fournaise volcano, Reunion Island, from U-series disequilibria. Earth Planet Sci Lett, 234: 223-234.

Staudacher T, 2010. Field observations of the 2008 summit eruption at Piton de la Fournaise (Ile de La R'eunion) and implications for the 2007 Dolomieu collapse. J Volc Geotherm Res, 191: 60-68.

Staudacher T, Ferrazzini V, Peltier A, Kowalski P, Boissier P, Catherine P, Lauret F, Massin F, 2009. The April 2007 eruption and the Dolomieu crater collapse, two major events at Piton de la Fournaise (La Reunion Island, Indian Ocean). J Volc Geotherm Res, 184: 126-137.

Stieltjes L, 1985. Carte des coulees historiques du volcan de la Fournaise. Bur Recherches Geol Minieres France, 1:50,000.

Stieltjes L, Moutou P, 1989. A statistical and probabilistic study of the historic activity of Piton de la Fournaise, Reunion Island, Indian Ocean. J Volc Geotherm Res, 36: 67-86.

Zlotnicki J, Le Mouel J L, Delmond J C, Pambrun C, Delorme H, 1993. Magnetic variations on Piton de la Fournaise volcano. Volcanomagnetic signals associated with the November 6 and 30, 1987, eruptions. J Volc Geotherm Res, 56: 281-296.

Volcano Types

Shield
Caldera(s)
Pyroclastic cone(s)

Tectonic Setting

Intraplate
Oceanic crust (< 15 km)

Rock Types

Major
Basalt / Picro-Basalt
Trachybasalt / Tephrite Basanite

Population

Within 5 km
Within 10 km
Within 30 km
Within 100 km
55,859
55,859
246,792
717,820

Affiliated Databases

Large Eruptions of Piton de la Fournaise Information about large Quaternary eruptions (VEI >= 4) is cataloged in the Large Magnitude Explosive Volcanic Eruptions (LaMEVE) database of the Volcano Global Risk Identification and Analysis Project (VOGRIPA).
WOVOdat WOVOdat is a database of volcanic unrest; instrumentally and visually recorded changes in seismicity, ground deformation, gas emission, and other parameters from their normal baselines. It is sponsored by the World Organization of Volcano Observatories (WOVO) and presently hosted at the Earth Observatory of Singapore.
EarthChem EarthChem develops and maintains databases, software, and services that support the preservation, discovery, access and analysis of geochemical data, and facilitate their integration with the broad array of other available earth science parameters. EarthChem is operated by a joint team of disciplinary scientists, data scientists, data managers and information technology developers who are part of the NSF-funded data facility Integrated Earth Data Applications (IEDA). IEDA is a collaborative effort of EarthChem and the Marine Geoscience Data System (MGDS).
Smithsonian Collections Search the Smithsonian's NMNH Department of Mineral Sciences collections database. Go to the "Search Rocks and Ores" tab and use the Volcano Name drop-down to find samples.