Rincon de la Vieja

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  • 10.83°N
  • 85.324°W

  • 1916 m
    6284 ft

  • 345020
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Most Recent Weekly Report: 17 September-23 September 2014


OVSICORI-UNA reported that at 1237 on 17 September a seismic signal indicating a phreatic explosion at Rincón de la Vieja was detected by a station about 5 km S of the volcano. A second phreatic explosion, detected at 2048 and lasting three minutes, was of a larger magnitude and a longer duration that the first explosion. Phreatic explosions were also detected at 1825 on 19 September and at 0304, 0439, and 0634 on 20 September. Residents on the N flank heard the event on 19 September and saw the explosion at 0634 on 20 September. An overflight of the crater lake on 20 September revealed that the temperature of the lake water was about 45 degrees Celsius, an increase from about 30 degrees measured in April.

Source: Observatorio Vulcanologico y Sismologico de Costa Rica-Universidad Nacional (OVSICORI-UNA)


Most Recent Bulletin Report: April 2011 (BGVN 36:04)


Fumarolically active but non-eruptive through January 2011

Low-frequency earthquakes and tremor were reported at Rincón de la Vieja during the first half of 2008 (BGVN 33:07). Since then, Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA) had issued intermittent reports of activity through January 2011. Those reports are summarized in the following sections, with much of the discussion centered around fumaroles and behavior of the geothermally warmed lake in the active crater. Occasional, typically small phreatic eruptions had occurred here in past years, for example in the 1990s (eg., BGVN 21:02, 21:03, 22:01, and 23:03) but were absent in the current reporting interval (last half of 2008 through January 2011).

August 2008. OVSICORI-UNA reported that the level of the lake was at a high level, with a bluish color, generated convection cells with evaporation, and had sulfur particles visible on it's surface. Sulfur deposition and fumarolic activity continued along the SW wall.

March 2009. In mid-March 2009, scientists visited the S and SW flank, collected samples, and noted some temperatures of 75-78°C. Because the visit occurred during the dry season, most areas encountered were dry. The scientists examined an area of acidification to the W of Von Seebach crater, ~3 km SW of the active crater. Strong winds common in that direction sometimes carried volcanic gases. Consequently, most of this narrow expanse only contained patches of grassland and shrubs that barely covered the rocky surface.

October 2009. OVSICORI-UNA reported that seismographic station RIN3, located ~5 km SW of the main crater, registered volcano-tectonic events and tremor lasting for minutes.

Weak ongoing fumarolic activity during 2010 through January 2011. OVSICORI-UNA reported that the level of the crater lake remained high during 2010, with constant evaporation. Geochemical, seismic, and deformation data did not show significant changes in physico-chemical parameters during 2010. The changing color of the lake, from blue to gray, was attributed to intense rains and fumarolic activity in the crater.

Later reporting. Reports during 2010 through at least January 2011 described fumarolic activity along the S and SW walls of the crater, with sulfur deposition and moderate gas discharge. The lake remained a gray color, with sulfur particles in suspension. Figure 15 shows a photo taken in April of the crater looking at the SW wall with fumarolic activity along with sulfur deposition. In April 2010, OVSICORI-UNA reported that the temperature of the lake was 49°C. A fumarole sometimes seen active along the N flank had stopped discharging gas.

Figure 15. Photo of the active crater lake of Rincón de la Vieja on 29 April 2010 showing yellow sulfur deposits and fumarolic activity along the SW wall of the crater. This kind of activity was typical throughout the reporting interval (last half of 2008 through January 2011). Photo by E. Fernandez, OVSICORI-UNA.

OVSICORI-UNA reported that 2010 was unusual in that four domestic volcanoes were active: Arenal, Poás, Turrialba, and Rincón de la Vieja. Irazú was comparatively inactive (see separate report in this issue of the Bulletin).

Information Contacts: E. Fernández, W. Sáenz, E. Duarte, M. Martínez, S. Miranda, F. Robichaud, T. Marino, M. Villegas, and J. Barquero, Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/).

Index of Weekly Reports


2014: September
2013: February
2012: February | April
2011: September

Weekly Reports


17 September-23 September 2014

OVSICORI-UNA reported that at 1237 on 17 September a seismic signal indicating a phreatic explosion at Rincón de la Vieja was detected by a station about 5 km S of the volcano. A second phreatic explosion, detected at 2048 and lasting three minutes, was of a larger magnitude and a longer duration that the first explosion. Phreatic explosions were also detected at 1825 on 19 September and at 0304, 0439, and 0634 on 20 September. Residents on the N flank heard the event on 19 September and saw the explosion at 0634 on 20 September. An overflight of the crater lake on 20 September revealed that the temperature of the lake water was about 45 degrees Celsius, an increase from about 30 degrees measured in April.

Source: Observatorio Vulcanologico y Sismologico de Costa Rica-Universidad Nacional (OVSICORI-UNA)


27 February-5 March 2013

OVSICORI-UNA received reports at 0530 on 26 February of pulsing white plumes rising from Rincon de la Vieja's active crater about every four minutes. The seismic records showed no signals associated with a phreatic eruption or sudden gas output. Cloud cover prevented views of the active crater during an overflight later that day, however clear views of the N and S flanks and areas SW showed no changes.

Source: Observatorio Vulcanologico y Sismologico de Costa Rica-Universidad Nacional (OVSICORI-UNA)


11 April-17 April 2012

OVSICORI-UNA reported that a small phreatic eruption occurred within and around the hot acidic lake of Rincon de la Vieja at 1400 on 14 April. Observers from nearby communities N of the volcano reported some sediment deposition along the outer N flanks of the main active crater and a white steam plume rising to a considerable height above the crater.

Source: Observatorio Vulcanologico y Sismologico de Costa Rica-Universidad Nacional (OVSICORI-UNA)


22 February-28 February 2012

OVSICORI-UNA reported that seismic data revealed two eruptions on 19 and 20 February from Rincón de la Vieja's active crater. Two more eruptions also occurred on 23 February. Explosions were heard in Guachipelin (11 km SW) between 0400 and 0430.

Source: Observatorio Vulcanologico y Sismologico de Costa Rica-Universidad Nacional (OVSICORI-UNA)


28 September-4 October 2011

On 30 September, OVSICORI-UNA reported phreatic eruptions from Rincón de la Vieja's active crater during the previous six weeks. A well-documented event on 16 September ejected sediment that covered sections of the upper N walls. Some of the material was washed down the flanks and caused changes in water quality along the main creeks and major rivers up to 18 km away from the source. The death of several fish species was noted the next day and sediment deposits 10-15 cm deep were sampled 2 km N of the active crater. Scientists conducting fieldwork during 27-29 September observed that the hot lake was convecting and grayish in color due to the suspended sediments. Preliminary deformation and temperature measurements did not indicate any significant changes.

Source: Observatorio Vulcanologico y Sismologico de Costa Rica-Universidad Nacional (OVSICORI-UNA)


Index of Bulletin 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.

05/1969 (CSLP 41-69) Ash eruption on 22 April

06/1969 (CSLP 41-69) No signs of activity observed

09/1969 (CSLP 41-69) Ashfalls on 20 September

08/1970 (CSLP 73-70) New eruption on 25 August produces great ash clouds

11/1982 (SEAN 07:11) No activity at the summit crater

03/1983 (SEAN 08:03) Tephra eruption from crater lake

04/1986 (SEAN 11:04) Tephra and trees down from fall 1985 eruption

02/1987 (SEAN 12:02) Small explosion

04/1987 (SEAN 12:04) Phreatic eruption; lahars

04/1989 (SEAN 14:04) Crater lake sampled

09/1990 (BGVN 15:09) Continued fumarolic activity; drop in crater lake water level

04/1991 (BGVN 16:04) Ash ejection and lahars

05/1991 (BGVN 16:05) More details on 8 May eruption and deposits

07/1991 (BGVN 16:07) Seismicity and tremor

08/1991 (BGVN 16:08) Explosions eject ash and blocks

02/1992 (BGVN 17:02) Gas emission and sporadic phreatic eruptions

03/1992 (BGVN 17:03) Small explosions and rumbling; earthquakes

05/1992 (BGVN 17:05) Thermal activity from crater lake; occasional seismicity

06/1992 (BGVN 17:06) Continued fumarolic activity

08/1992 (BGVN 17:08) Strong degassing; explosion seismicity

09/1992 (BGVN 17:09) Strong fumarolic activity; seismic swarm

10/1992 (BGVN 17:10) Degassing and minor seismicity

01/1993 (BGVN 18:01) Fumaroles; minor seismicity

02/1993 (BGVN 18:02) Gas plumes rise to 500 m; lake level drops

03/1993 (BGVN 18:03) Hour-long earthquake swarm

04/1993 (BGVN 18:04) Seismic activity continues

05/1993 (BGVN 18:05) Seismicity continues

09/1993 (BGVN 18:09) Crater lake level drops 10 m

01/1994 (BGVN 19:01) New seismic data, but still relatively quiet

03/1994 (BGVN 19:03) Subaqueous degassing; fractures surrounding SE crater rim

04/1994 (BGVN 19:04) Decreased seismicity

09/1994 (BGVN 19:09) Vigorous fumarolic activity

10/1994 (BGVN 19:10) Thirty-one small high-frequency events

11/1994 (BGVN 19:11) Vigorous fumarolic activity continues

12/1994 (BGVN 19:12) Minor seismicity

01/1995 (BGVN 20:01) Ongoing low-frequency seismic signals and fumarolic venting

04/1995 (BGVN 20:04) Description of the crater lake and fumaroles

09/1995 (BGVN 20:09) Seismic activity continues at a rate of tens of events per month

10/1995 (BGVN 20:10) New eruption; lahars damage a bridge and lead to evacuations

12/1995 (BGVN 20:11) Additional details about the 6-10 November eruption

01/1996 (BGVN 21:01) Eruption on 11-13 November followed by decreasing seismicity

03/1996 (BGVN 21:03) Mild seismicity continues in February

05/1996 (BGVN 21:05) Seven minor seismic events

06/1996 (BGVN 21:06) Six-fold seismic increase over previous months in 1996

08/1996 (BGVN 21:08) Small local earthquakes

01/1997 (BGVN 22:01) Sulfur-bearing steam, mass wasting, and acid rain in September

05/1997 (BGVN 22:05) Conspicuous fumaroles and plumes persist

09/1997 (BGVN 22:09) Variable but modest seismicity during June-September 1997

03/1998 (BGVN 23:03) Phreatic eruptions on 15-17 February thrust steam to 2 km

06/1998 (BGVN 23:06) Non-eruptive and relatively quiet seismically during April-June

06/1999 (BGVN 24:06) 1.5-year record of seismicity and eruptions through May 1999

03/2000 (BGVN 25:03) Non-eruptive through November 1999 but with ongoing tremor

11/2001 (BGVN 26:11) Fumarolically active through August 2001

10/2007 (BGVN 32:10) Continued fumarolic activity; sulfur floating in the lake

07/2008 (BGVN 33:07) Tremor durations from minutes to over an hour during June-April 2008

04/2011 (BGVN 36:04) Fumarolically active but non-eruptive through January 2011




Bulletin Reports

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


05/1969 (CSLP 41-69) Ash eruption on 22 April

Card 0521 (01 May 1969) Ash eruption on 22 April

"Initial activity appears to have occurred on 22 April at 1630 with ash eruption from 8,000 to 10,000 feet. No further ash eruptions reported. Observer also reports number of 'gas eruptions like funnel of ship' with increasing activity from 22 to 30 April with strong gas eruptions from 1300 to 1400 on 29 April. While volcanic activity at Rincón de la Vieja occurs relatively frequently, local opinion characterizes present eruptions as somewhat unusual."

Card 0531 (06 May 1969) Fumarole erupting dense gas

"Observation top crater Rincón de la Vieja obscured by heavy cloud cover, but observer reports a fumarole located at Quebrada Grande (same volcano) was erupting very strong and dense sulfuric gases. Observer reports this as being 'an extraordinary phenomenon.'"

Information Contacts: Card 0521 (01 May 1969) Richard Berg, American Embassy, San José, Costa Rica.
Card 0531 (06 May 1969) Richard Berg, American Embassy, San José, Costa Rica.

06/1969 (CSLP 41-69) No signs of activity observed

Card 0568 (04 June 1969) No signs of activity observed

The following is from a cable received on 3 June. On or about 21 May Rodrigo Sáenz observed the main crater and reports no sign of activity.

Information Contacts: Richard Berg, American Embassy, San José, Costa Rica

09/1969 (CSLP 41-69) Ashfalls on 20 September

Card 0763 (24 September 1969) Ashfalls on 20 September

The following cable was received on 23 September. "Volcanic ash fell on Liberia and surrounding areas during early a.m., early p.m., and late p.m. on 20 September 1969 reportedly from eruption of Rincón de la Vieja. Because of heavy rains and cloud cover on 21 and 22 September impossible to report any further details whether activity is continuing at this time."

Information Contacts: Richard Berg, American Embassy, San José, Costa Rica.

08/1970 (CSLP 73-70) New eruption on 25 August produces great ash clouds

Card 0996 (26 August 1970) New eruption on 25 August produces great ash clouds

The following cable was received on 25 August 1970. "A new eruption of the Rincón de la Vieja volcano was reported at 1100 GMT, 25 August with great clouds of ashes and smoke. The first eruption of the volcano was reported at 0549 local time 25 August. Dispatches received from Liberia reported that the volcanic activity is similar to that of the last eruption of the Irazu volcano."

Card 0999 (27 August 1970) Most ash blown over the ocean

The following cable was received on 27 August 1970 from the American Embassy. "Rodrigo Sáenz reports single eruption at Rincón de la Vieja at 0500 on 25 August produced minor ash cloud. Some ashfall over Liberia but most apparently blown to sea by winds. Ash clouds height estimated 1,000 feet. Sáenz states eruption similar to one he witnessed 14 August. No eruptions occurred between 14 and 25 August."

Information Contacts: Card 0996 (26 August 1970) Rodrigo Sáenz R., Seccion Sismologica y Vulcanologia de Industria y Comercio, San José, Costa Rica (via San José Radio).
Card 0999 (27 August 1970) Rodrigo Sáenz R., Seccion Sismologica y Vulcanologia de Industria y Comercio, San José, Costa Rica. T. Solitario, American Embassy, San José, Costa Rica.

11/1982 (SEAN 07:11) No activity at the summit crater

"In November the odor of H2S was present from the summit crater, but there was no visible gas plume and no eruptive activity. Low-temperature steam vents and mudpots persisted at Estación las Pailas, at the foot of the volcano."

Information Contacts: R. Stoiber, S. Williams, H.R. Naslund, C. Connor, J. Prosser, and J.B. Gemmell, Dartmouth College; E. Malavassi and J. Barquero H., Univ. Nacional, Heredia.

03/1983 (SEAN 08:03) Tephra eruption from crater lake

This paragraph is primarily from a report by Jorge Barquero H. and Juan de Dios Segura. During the night of 6 February, residents of towns (Dos Ríos de Upala, Colonia Blanca, and Colonia Libertad) 8 km N and NE of the volcano heard strong rumblings and observed the rise of a large eruption column from the crater. Personnel from the Proyecto de Investigaciones Vulcanológicas climbed the volcano 19 February. The odor of sulfur was stronger than it had been during their previous ascent in November 1982. Phreatomagmatic eruptions had ejected bombs, lapilli, and ash, as well as blocks 10-100 cm in diameter that formed impact craters. Tephra fell SE, S, and SW of the vent to a distance of about 1.5 km. Destruction, primarily to vegetation, was greatest to the SE and S. The tephra had a high water content because the vent contained a lake. Strong rains and rapid erosion since the eruption made it difficult to calculate the original depth of the airfall deposits, although in some places SE of the vent they were 4 cm thick. The eroded ash washed into a ravine, producing a small mudflow in a NE flank river (Río Pénjamo), causing the deaths of thousands of fish 7-8 February, possibly because of the acidity of the water. The pH of the cold lake was 3.5 on 19 February and 4.1 on 5 March.

Jorge Barquero H., J. Bruce Gemmell, and Jerry Prosser climbed the volcano on November 1982, and Gemmell provided the following report. "Rincón de la Vieja is a large composite volcano with a series of collapse craters aligned ENE-WSW. Its main cone is covered with thick vegetation but three craters to the W are not vegetated. The most recently active crater (250 m in diameter) is 1 km NW of the main cone. No activity or gas emissions were seen in this crater and a cold yellowish-green lake covered the crater floor. No steam was rising from the lake but two areas of brown discoloration near its center may have indicated subaqueous vents. The area around the summit craters was covered with accessory blocks of andesitic lava and tuff breccias, in addition to juvenile andesitic breadcrust bombs, lapilli, and ash from the most recent recorded eruptions in 1966-70. Numerous mudpots, hot springs, and steam vents occurred in two main areas (Aguas Termales and Sitio Hornillas), on the S flank at about 900 m elevation."

Further Reference. Barquero, J., and de Diós Segura, J., 1983, La Actividad del Volcán Rincón de la Vieja: Boletín de Vulcanología, no. 13, p. 5-10.

Information Contacts: J. Barquero H. and J. de Dios Segura, Univ. Nacional, Heredia; J.B. Gemmell and J. Prosser, Dartmouth College; R. Sáenz R., Ministro de Energía y Minas; La República, San José.

04/1986 (SEAN 11:04) Tephra and trees down from fall 1985 eruption

The following reports are from the Observatorio Vulcanológico y Sismologico de Costa Rica (OVSICORI). "After several attempts to climb to the summit of Rincón de la Vieja were turned back by bad weather, we reached the active crater on 19 April with W. Melson of the Smithsonian Institution. During this visit, we were able to confirm that there had been a recent eruption, since we encountered recently erupted material and a devastated area, both SE of the crater.

"At the time of our previous ascent, in August 1985, this tephra had not been deposited. In a photograph taken 25 November 1985 by E. Valverde, it is possible to observe white tephra. In addition, the seismic station at the base of the volcano registered an increase in activity (harmonic tremor and A- and B-type events) between September and November, suggesting that the eruption occurred during that time.

"A fan-shaped area of about 0.25 km3 was affected. The ejecta reached a maximum distance of 500 m SE of the active crater. The erupted material is secondary, including ash, sand, and blocks as much as 20 cm across. On one rock, an ash deposit 6 cm thick was observed. The effect of the eruption on rain forest vegetation was marked about 500 m SE of the crater (in the E bank of the Quebrada Azufrosa) where trees had been knocked down in a radial pattern by the activity. This pattern is unusual in that the fallen trees appeared to radiate from a point near their center, not from the crater. In addition, various plant species in this area were affected by the acid in the pyroclastics and the associated water.

"On 19 April there was a strong and constant emission of gas that affected breathing because of its acidity, and made it difficult to observe the lake in the active crater."

Information Contacts: J. Barquero and E. Fernández Soto, OVSICORI.

02/1987 (SEAN 12:02) Small explosion

"Alfonso Bustos of Upala, a town about 35 km NE of the volcano, reported that he observed an eruption of Rincón de la Vieja during the night of 31 December 1986. The seismological station of the Observatory, located on the volcano, registered an eruptive event at 2307:13 with a duration of 6 minutes 13 seconds. The period of highest amplitude was constant at one second.

"Because of weather problems in the region, we could not climb to the summit until 7 February 1987, when we verified that a small eruption had recently occurred. The affected area was the S and SE parts of the active crater, where eruptive materials were encountered to 500 m distance. At the crater rim, 10 cm of ash was measured and there were blocks 50 cm long by 40 cm wide. No evidence of juvenile material was encountered. Some plants had burns on their leaves, possibly caused by the acidity of ash deposited on them and the acidity of water that accompanied the ejecta; the eruptions occurred in a crater with a lake. The activity during the day of the ascent was constant emission of gas with a strong sulfurous odor that irritated the eyes and annoyed everyone that we encountered near the crater."

Information Contacts: J. Barquero and E. Fernández Soto, OVSICORI.

04/1987 (SEAN 12:04) Phreatic eruption; lahars

"On 1 April, an eruption of Rincón de la Vieja was heard and seen by residents of the town of Buenos Aires de Upala, 7 km NE of the crater. This phreatic eruption originated from the active crater.

"Various rivers have headwaters on the N flank and flow NE (among them the Río Azul, Quebrada Azufrada, and Río Pénjamo) and lahars formed in some of them. At about 500 m above sea level, the Río Pénjamo and the Quebrada Azufrada left their channels, flooding agricultural land. No lahar formed in the Río Azul, although on 9 April it still had a gray color because of the quantity of suspended ash that it was carrying.

"According to a resident of the area, the eruption occurred at 0940. Twenty minutes later the lahar passed near the town of Buenos Aires. The seismic station of the Observatorio Vulcanológico y Sismológico registered an event at 0932.55 with a duration of 3 minutes."

Information Contacts: J. Barquero, OVSICORI.

04/1989 (SEAN 14:04) Crater lake sampled

Geologists sampled the crater lake on 6 April. The lake temperature was 45°C, determined by throwing a bottle 100 m into the lake, measuring the resulting sample with a thermocouple, and applying a cooling correction.

Information Contacts: David Stevenson, Open Univ.

09/1990 (BGVN 15:09) Continued fumarolic activity; drop in crater lake water level

Evaporation of the crater lake was noted during fieldwork at the volcano the third week in July. Strong fumarolic activity continued within the lake, and a sulfur odor was detected near the summit, roughly 100 m above the lake.

Information Contacts: J. Barquero, E. Fernández, and V. Barboza, OVSICORI.

04/1991 (BGVN 16:04) Ash ejection and lahars

A [phreatomagmatic] eruption at 1015-1025 on 8 May ejected small quantities of [ash, bombs, blocks, and mud, and produced small lahars]. Gray lahars with a sulfur odor traveled N down the Río Pénjamo and Azul systems, destroying the forest along the rivers and two small bridges, and cutting off access to the towns of Buenos Aires (12 km NE) and Gavilán. At the distal end of the lahars, 15 km from the summit, the deposits reached 2 m in thickness, and covered the surface for several hundred meters on both sides of the Pénjamo river channels. Following passage of the lahars, the rivers were milky and had high acidity. The eruption followed two smaller explosive events on 6 and 7 May, but no other seismic precursors were recorded.

Information Contacts: R. Barquero, ICE; J. Barquero and R. Sáenz, OVSICORI.

05/1991 (BGVN 16:05) More details on 8 May eruption and deposits

The following, from the Univ Nacional, supplements last month's report from ICE.

A phreatic eruption on 8 May ejected lake sediments and ash, and produced small mudflows. The eruption followed several low-frequency earthquakes during the night of 6-7 May, and a low-frequency earthquake with a 155-second duration at 0811 on 7 May. Reports from residents of Dos Ríos de Upala (8 km NW) and from guards at Parque Nacional Rincón de la Vieja described an accompanying explosion and a 1-km-high light-colored plume with ash that traveled NW.

Seven low-frequency microearthquakes preceded the 8 May phreatic eruption. An earthquake that lasted 120 seconds, possibly associated with a small explosion, occurred 18 minutes prior to the eruption, and low-frequency tremor began 7 minutes before it.

The sound wave of the main explosion arrived at the seismometer (6 km SW) 6 seconds after the start of the eruption signal at 1017, and the instrument was saturated for 25 seconds. The subsequent 150-second signal was interpreted to record strong degassing and the initiation of mudflows. Low-frequency harmonic tremor was recorded for 30 minutes, gradually decreasing below detection limits. The main explosion produced a gray ash cloud, 5 km high, that was carried NW. Ash was deposited to 14 km NW from this (figure 1) and the approximately 10 small (columns <1 km high) explosions that were observed, but not recorded, from 1153 to 1205. Sulfur odor, itchy skin, and eye irritation were reported 28 km WNW (at Cruz de Piedra). Another 23 low-frequency earthquakes were recorded later that day.

Figure 1. Map showing deposits from the 8 May 1991 phreatic eruption at Rincón de la Vieja. Site numbers correspond to cross-sections in figures 2 and 3, and table 1. Courtesy of OVSICORI.

Table 1. Field observations of 8 May 1991 mudflow deposits from Rincón de la Vieja. Sites correspond to locations in figure 1. Courtesy of OVSICORI.

    Site  Distance  Deposit  Channel  Max. flow     Deposit
                     width    width    height     description

     1     7.2 km     41 m    10 m     4-6 m     1.65 m of erosion.
     2     6.6 km    185 m    12 m     2-3 m     ~8 m deposited.
     3     7.0 km    239 m     **      4-5 m     2-60 cm of fine
                                                 (2-16 mm) material.
     4    16.6 km     **       **      2.15 m    Blocks (to 1.5 x 2.0
                                                 m) and tree trunks
                                                 (50 cm diameter);
                                                 10-50-cm mantle of
                                                 fine sediment.

Mudflows traveled down the N flank (along the Quebrada Azufrosa, and Río Pénjamo), destroying two small bridges and cutting off access to the towns of Buenos Aires (~12 km NE) and Gavilán. Several smaller mudflows traveled down tributaries to the Río Azul (also to the N). Erosion occurred predominantly between 1,500 and 500 m elevation. Field observations of the mudflow deposits were made at several sites (figures 2 and 3; table 1). Park guards reported small quantities of sediment transported by the Río Colorado (S flank), but no effects on the ecosystem were observed.

Figure 2. Cross-section of 8 May 1991 Rincón de la Vieja mudflow deposits near a bridge over the Río Azul. Site location is marked in figure 1. Courtesy of OVSICORI.
Figure 3. Cross-section of 8 May 1991 Rincón de la Vieja mudflow deposits near a bridge over the Río Pénjamo. Site location is marked in figure 1. Courtesy of OVSICORI.

Blocks (to 40 x 50 cm) with impact craters and ejected lake sediments were found near the summit during a 9 May visit. Acidity and sediment-fall had variable impacts on nearby vegetation, ranging to complete defoliation. Fumarolic activity continued, as evidenced by a strong sulfur odor, eye irritation, and breathing difficulties near the crater. Rain collected 3 km S had a pH of 3.85.

Seismicity declined to 9 low-frequency recorded earthquakes/day (9 May), with only sporadic (1-2/day) events on later days.

Information Contacts: E. Fernández S., Jorge Brenes M., V. Barboza M., and Tomás Marino H., Observatorio Vulcanológico y Sismológico de Costa Rica, Univ Nacional.

07/1991 (BGVN 16:07) Seismicity and tremor

A total of 399 microearthquakes were recorded in July (figure 4) at a seismic station (RIN3) 6 km SW of the crater. Six hours of low- and medium-frequency tremor (1.3-3.2 Hz), were recorded in episodes 12 minutes to 3 hours long. Low-frequency earthquakes were also recorded, with durations that reached 175 seconds.

Figure 4. Daily number of earthquakes at Rincón de la Vieja, July 1991. Courtesy of OVSICORI.

Information Contacts: J. Barquero, E. Fernández, V. Barboza, and J. Brenes, OVSICORI.

08/1991 (BGVN 16:08) Explosions eject ash and blocks

After reports of strong sulfur odors, geologists visited the summit area on 28-30 August. A sulfurous odor was noted at Copelares on the S flank (1,400 m elevation), during the evening of 28 August. An explosion was heard at 0151 the next morning, followed several seconds later by the sound of falling material. Examination of 29 August records from a seismic station 6 km SW of the crater (RIN3) showed that a small earthquake occurred at 0148:47, then a larger earthquake sequence lasting 7.5 minutes began at 0151:40, coinciding with the first audible explosion. As the ascent continued later that morning, traces of fresh ash were observed beginning at about 1,500 m elevation. Large quantities of ash and blocks, ranging from 15 to 75 cm in diameter, were found deposited in the summit area. Impact craters reached 120 cm in diameter and 35 cm deep.

Bad weather obscured the view of the crater floor, but several explosions were heard, and the largest, at 0930, rained very wet ash on the scientists. Near the crater, the smell of sulfur was very strong, making breathing difficult and stinging the eyes. Nearby vegetation was partially or completely dead. Rain collected at Copelares had a pH of 4.1.

On 30 August, scientists visited Ríos Azul and Pénjamo, which flow down the N flank from the crater area. Both rivers were gray-white with suspended sediment, which was also visible, but in lower concentrations, in the Ríos Colorado and Blanco on the S and SE flanks.

[On 6 September, strong fumarolic activity (jet engine noise) was seen in the active crater. During explosive events of May-August 1991 the ejecta was mainly composed of gray mud (sulfide-rich), lithics, and bread-crust bombs (~10% by volume).]

Information Contacts: J. Barquero and E. Fernández, OVSICORI; R. Barquero and G. Soto, ICE; Mario Fernández, Héctor Flores, and Sergio Paniagua, Univ. de Costa Rica.

02/1992 (BGVN 17:02) Gas emission and sporadic phreatic eruptions

Gas emission has continued over the last several months, punctuated by sporadic phreatic eruptions. Fumarolic activity was concentrated on the active crater's E wall, producing a plume that occasionally reached 500 m height, smelling of sulfur, and irritating eyes and skin. The crater lake was gray, with yellow areas over bubbling points. Concentric and radial fissures, to 1 m wide and to >4 m deep, were found on the upper E, N, and NW flanks. The fissures were probably formed by partial collapse of the crater walls, especially on the E and NW flanks. Seven low-frequency earthquakes were recorded during February, down from a peak of 30 recorded 8 May 1991, associated with a large phreatic eruption. Abnormal seismicity was reported for several months after 8 May.

Information Contacts: E. Fernández, J. Barquero, V. Barboza, and R. Van der Laat, OVSICORI.

03/1992 (BGVN 17:03) Small explosions and rumbling; earthquakes

Rumbling and small explosions were reported on several occasions in March. Portable seismometers at Proyecto Geotérmico Miravalles (35 km SE of the active crater) recorded small earthquakes, possibly associated with explosions, on 13-16, 20, and 26 March. A maximum of five events was recorded, on 16 March.

Information Contacts: G. Soto and R. Barquero, ICE; Guillermo Alvarado, GEOMAR, Christian-Albrechts-Universität, Germany; Mario Fernández, Univ. de Costa Rica.

05/1992 (BGVN 17:05) Thermal activity from crater lake; occasional seismicity

The active crater lake (150-200 m diameter) was gray to dirty white during May fieldwork, with weak, intermittent bubbling. Fumarolic activity in the E part of the crater, where water was slightly greenish, was stronger than during February fieldwork. The activity, audible at the crater rim, produced a plume that rose more than 100 m (the height of the crater wall), and was visible several kilometers N. Crater-lake level had dropped about 30 cm since February, while the temperature remained at 37°C and the pH at 1.6. Small mats of sulfur were visible on the lake surface. Weak vapor emission began at several points along a fissure (first observed in February) near the SE and SW rim, with temperatures of 55°C and 60°C, respectively.

Six microearthquakes were recorded in May (at OVSICORI station RIN3, 5 km S). A 16-minute tremor episode (1-2.5 Hz) was recorded on 22 May.

Information Contacts: G. Soto, R. Barquero, and Guillermo E. Alvardo, ICE; Mario Fernández, Univ. de Costa Rica; E. Fernández, J. Barquero, and V. Barboza, OVSICORI.

06/1992 (BGVN 17:06) Continued fumarolic activity

Fumarolic activity continued through June in the active crater, where it had fed a plume more than 100 m high during May fieldwork. Chemical analyses of water collected 13 May showed pH values of less than 3 in two of the three N-flank rivers sampled, and some enhancement in sulfate and chloride concentrations (table 2). A seismographic station 5 km SW of the crater (RIN3) registered seven low-frequency earthquakes in June.

Table 2. Chemistry of water collected 13 May 1992 from three rivers on the N flank of Rincón de la Vieja. Data courtesy of the Univ. de Costa Rica.

    River     pH    Cl(-) (ppm)   SO4(-2) (ppm)
    Pénjamo   2.9      1.5            392
    Blanco    5.8      2.1            122
    Azul      2.4     10.0            384

Information Contacts: E. Fernández, J. Barquero, and V. Barboza, OVSICORI; G. Soto, ICE; Mario Fernández, Univ. de Costa Rica.

08/1992 (BGVN 17:08) Strong degassing; explosion seismicity

Strong degassing occurred in the active crater. Some seismic signals with durations of up to 3 minutes were recorded during August, interpreted by ICE geologists as probably associated with small or moderate eruptions from the hot crater lake. However, no deposits of mud were found on the crater rim during fieldwork on 28 August, so any deposition must have been confined to the interior of the crater. Parts of the rim rise >150 m above the lake. A UNA seismic station (RIN3) 5 km SW of the main crater recorded 11 low-frequency events in August, with brief (1-6 minute) periods of tremor at frequencies of <2.5 Hz.

Information Contacts: G. Soto and R. Barquero, ICE; E. Fernández, J. Barquero, and V. Barboza, OVSICORI.

09/1992 (BGVN 17:09) Strong fumarolic activity; seismic swarm

Intense fumarolic activity continued from the SE inner wall of the active crater (figure 5). The emissions were rich in water vapor and sulfurous gases, emerging with a jet-engine sound and rising 350 m above the level of the crater lake in the absence of wind. Sulfur cones formed at the vents. Four main hot areas were evident in the crater lake (near the center, and on the NW, N, and NE sides), which was about 250 m in diameter. The lake was colored gray by the large amount of muddy sediment that it carried in suspension. Strands of mud and sulfur floated on the lake surface. Its temperature was measured by the Instituto Costarricense de Electricidad (ICE) at 52°C on 25 September. Of the 403 events of medium to high frequency recorded in September, 388 occurred between 1 and 10 September, the period in which the medium-frequency seismicity (>2.5 Hz) was recorded (figure 6). Sporadic low-frequency harmonic tremor was detected for periods of up to 2.5 minutes.

Figure 5. Topographic map of the Rincón de la Vieja complex, showing the site of the currently active crater. A national park building near the Las Pailas thermal area on the lower S flank is marked P.N. Contour interval, 200 m below 1,400 m elevation, 100 m at higher altitudes. Courtesy of ICE.
Figure 6. Number of seismic events per day at Rincón de la Vieja, recorded by a UNA seismic station (RIN3), 5 km SW of the main crater. Courtesy of UNA.

Information Contacts: E. Fernández, J. Barquero, and V. Barboza, OVSICORI; G. Soto and R. Barquero, ICE.

10/1992 (BGVN 17:10) Degassing and minor seismicity

Degassing continued from the active crater. Seismic stations at the Proyecto Geotérmico de Miravalles (8-10 km from the active crater) continued to register 2-3 low-frequency volcanic events/day of <100 seconds duration. Vigorous seismicity had continued into early September, after seismic signals interpreted as probably associated with small to moderate eruptions from the lake were recorded in August.

Information Contacts: G. Soto and R. Barquero, ICE; E. Fernández, J. Barquero, and V. Barboza, OVSICORI.

01/1993 (BGVN 18:01) Fumaroles; minor seismicity

Fumarolic activity continued in the E wall of the active crater. A seismic station (RIN3) 5 km SW of the crater registered 30 high-frequency shocks on 26 January. The same day at 1646, a M 3.0 earthquake occurred 4 km NNE of the main crater at 9 km depth. No significant tilt changes were observed during the most recent measurements in November 1992.

Information Contacts: E. Fernández, J. Barquero, R. Van der Laat, F. de Obadía, T. Marino, and R. Sáenz, OVSICORI; M. Martini, Univ di Firenze, Italy.

02/1993 (BGVN 18:02) Gas plumes rise to 500 m; lake level drops

Fumarolic activity continued from the E wall of the active crater, with gas plumes rising 500 m. A strong smell of sulfur near the crater caused eye and skin irritation. Gas vents in the SE and SW parts of the crater had disappeared. Small collapses had occurred along the E and NE crater walls.

The level of the crater lake has dropped 1 m since last year. The light-gray colored lake had a temperature of 35°C in February and a pH of 1.6. The number of floating sulfur patches has decreased, and only one small bubbling area remains, producing very small intermittent bubbles.

Information Contacts: E. Fernández and J. Barquero, OVSICORI.

03/1993 (BGVN 18:03) Hour-long earthquake swarm

The seismic station 5 km SW of the main crater recorded an hour-long swarm of 10 volcano-tectonic earthquakes (M <1.9) on 26 March. Fumarolic activity continued inside the crater and in the crater lake.

Information Contacts: G. Soto and R. Barquero, ICE; E. Fernández, J. Barquero, V. Barboza, T. Marino, R. Van Der Laat, F. de Obaldía, and R. Sáenz, OVSICORI.

04/1993 (BGVN 18:04) Seismic activity continues

A seismograph about 5 km SW of the active crater recorded 28 microearthquakes and four high-frequency earthquakes in April (figure 7).

Figure 7. Seismic events/day recorded 5 km SW of the active crater of Rincón de la Vieja. Courtesy of OVSICORA.

Information Contacts: E. Fernández, J. Barquero, V. Barboza, and W. Jimenez, OVSICORI.

05/1993 (BGVN 18:05) Seismicity continues

A total of 40 seismic events was recorded in May at a station 5 km SW of the main crater: 35 middle- and low-frequency events, and five high-frequency shocks (1.2-3 Hz). Volcanic tremor peaked on 20 May when 1.5 hours were recorded. Tremor was also detected 23, 25, 27, and 30 May for 11, 8, 3, and 8 minutes, respectively.

Information Contacts: E. Fernández, J. Barquero, F. De Obaldía, T. Marino, R. Van Der Laat, V. Barboza, and R. Sáenz, OVSICORI.

09/1993 (BGVN 18:09) Crater lake level drops 10 m

A visit to the active crater on 6 October took place in bad weather, but scientists found strong fumarolic activity and a >10 m drop in lake level compared to September 1992. The lake level began changing after the 8 May 1991 phreatic eruption.

Low-frequency microseismic activity increased over the last 3 months, with three events in July, five events in August, and 93 events in September. Tremor was not reported in July, 165 minutes of tremor occurred in August, and no tremor was detected in September. Dry-tilt for the interval from November 1992 to July 1993 indicated an 11 µrad radial deflation; in contrast, the majority of intervals as far back as 1987 showed little or no change.

Information Contacts: E. Fernández, J. Barquero, R. Van der Laat, F. de Obaldia, T. Marino, V. Barboza, and R. Sáenz, OVSICORI; G. Soto, Guillermo E. Alvarado, and Francisco Arias, ICE; Héctor Flores, Univ. de Costa Rica.

01/1994 (BGVN 19:01) New seismic data, but still relatively quiet

During 1993 Rincón de la Vieja continued fumarolic venting in Rincón crater. Gas columns rose to 500 m high and contained sufficient gas concentrations to irritate the eyes and sting the skin of observers on the crater margin. The crater lake was clear gray in color, with clouds of suspended sulfur and several areas of discontinuous bubbling. It had a temperature of 35°C.

When seismically active, as in January and September 1993 (figure 8), both high- and low-frequency signals were common. A swarm of 25 high-frequency events took place on 26-29 January. On 26 March, 10 small-amplitude high-frequency events registered, their S - P (S minus P) times were <1.6 seconds. In January 1993 there was a lapse of 16 days in the record, and consequently the number of earthquakes for the month on figure 8 was adjusted [assuming the other recorded days suitably reflect the average seismicity for the whole month]. The January 1994 events were of low-frequency, some with durations over 1 minute. Until July 1993 the volcano deflated radially at a rate of 11 µrad/year; in contrast, the majority of intervals as far back as 1987 showed little or no change. Deflation was unreported in August through January.

Figure 8. Seismic events at Rincón de la Vieja received at station RIN3, 5 km SW of the active crater, January 1993-January 1994 (October-December 1993 data presumed unrecorded). Courtesy of OVSICORI.

Information Contacts: E. Fernández, J. Barquero, R. Van der Laat, F. de Obaldia, T. Marino, V. Barboza, and R. Sáenz, OVSICORI.

03/1994 (BGVN 19:03) Subaqueous degassing; fractures surrounding SE crater rim

During March, Rincón de la Vieja continued fumarolic and seismic activity. The crater lake, which was 40 cm below the level seen in June 1993, had a temperature of 36°C. The lake had a clear gray color, although a fog of condensed gases hovering over the lake hampered visual observations. Visitors noted that vigorous, noisy fumaroles in the E crater wall produced enough sulfurous fumes to provoke coughing and irritate the eyes and skin. Fumes have also injured the already sparse vegetation adjacent to the active crater.

ICE researchers reported "sporadic and intermittent bubbling events (up to several meters in height and diameter) rising up from the center and SE portions of the warm lake, producing strong waves and noise, and giving a muddy-gray color to the lake." They also saw new, open fractures surrounding the SE crater rim.

In the interval February-March 1993, Rincón's seismic station registered an increase in events of low frequency (0.5-1.3 Hz) with durations [of] 25-150 seconds (figure 9). When previously seismically active, as in January and September 1993, both high- and low-frequency signals were common.

Figure 9. Seismic events at Rincón de la Vieja received at station RIN3, 5 km SW of the active crater, January-March 1994. Courtesy of OVSICORI.

Information Contacts: Gerardo J. Soto, Guillermo E. Alvarado, and Francisco (Chico) Arias, ICE; E. Fernández, J. Barquero, R. Van der Laat, F. de Obaldia, T. Marino, V. Barboza, and R. Sáenz, OVSICORI.

04/1994 (BGVN 19:04) Decreased seismicity

During April, the local seismic station received only 13 low-frequency events. In contrast, there were 283 low-frequency events during the previous month, the most so far this year. Neither the increase nor the decrease in seismicity were associated with any other observed changes.

Information Contacts: E. Fernández, J. Barquero, V. Barboza, and W. Jiménez, OVSICORI; G. Soto, Guillermo E. Alvarado, and Francisco (Chico) Arias, ICE; Héctor (Chopo) Flores, Univ. de Costa Rica.

09/1994 (BGVN 19:09) Vigorous fumarolic activity

Fumarolic activity in the main crater remained vigorous during August and September. Preliminary processing of seismicity recorded by ICE with a portable digital station 2.2 km S of the crater during fieldwork in late August indicated several hundred low-frequency earthquakes beneath the crater, and background tremor-like activity. The preliminary interpretation is that the low-frequency seismicity is caused by hydrothermal circulation among a shallow magma body, aquifers, and the lake system. The OVSICORI-UNA seimic station (5 km SW of the active crater) registered 15 high-frequency low-magnitude events during September.

From the village of México (40 km NE), early morning observations during late September and early October by an ICE geologist revealed a steam-rich gas column rising up to 1 km above the crater. This is higher than the 300-400 m estimated in March.

Information Contacts: E. Fernandez, J. Barquero, V. Barboza, R. Van der Laat, T. Marino, F. de Obaldia, and L. Carvajal, OVSICORI; G. Soto, W. Taylor, F. Arias, G. Alvarado, and R. Barquero, ICE; Mauricio Mora, Univ. de Costa Rica.

10/1994 (BGVN 19:10) Thirty-one small high-frequency events

Seismic station RIN (5 km W of the active crater) received 31 events of high-frequency. The events were only detected locally, they had Richter magnitudes of less than 1, and S minus P times of less than 2 seconds. For comparison, during April, the local seismic station received only 13 low-frequency events. In contrast, there were 283 low-frequency events during the previous month, the most reported so far this year.

Information Contacts: E. Fernández, J. Barquero, and V. Barboza, OVSICORI.

11/1994 (BGVN 19:11) Vigorous fumarolic activity continues

The fumarolic activity in the main crater that remained vigorous during August and September, continued in November. A seismic record made by ICE in November suggested seismo-volcanic activity of low frequency and magnitude located at very shallow depths beneath the crater.

Information Contacts: E. Fernández, J. Barquero, R. Van der Laat, F. de Obaldia, T. Marino, V. Barboza, and R. Sáenz, OVSICORI; G. Soto, Guillerma E. Alvarado, and Francisco (Chico) Arias, ICE.

12/1994 (BGVN 19:12) Minor seismicity

During December 1994, Rincón de la Vieja was seismically active. The local station (5 km SW of the active crater) registered three small-amplitude events on 19 December and, at 2121, a fourth of Richter magnitude 3.0. The last event had a focal depth of 23 km and an epicenter 4.5 km NE of the active crater. One event took place each day on 23, 24, and 25 December; these events each had an S -P delay in the range of 1.9 to 2.5 seconds.

Information Contacts: OVSICORI.

01/1995 (BGVN 20:01) Ongoing low-frequency seismic signals and fumarolic venting

During January Rincón de la Vieja continued fumarolic venting from the main crater. ICE reported that they continued to record seismic signals of low-frequency and magnitude at the volcano. They interpreted the signals as seismo-volcanic activity at shallow depth beneath the main crater.

Information Contacts: ICE.

04/1995 (BGVN 20:04) Description of the crater lake and fumaroles

The remote Rincón de la Vieja volcanic complex continues to display unsettled seismic and fumarolic activity. OVSICORI-UNA reported that during April fumarolic venting continued from the W wall, creating noise audible from the crater's rim. Escaping gases stung the skin. Radial fractures encircled the crater on its NE, N, and NW sides.

G. Soto (ICE), Jean-Philippe Rancon, and Gorges Boudon climbed the volcano on 1 May and reported that the lake contained a scum of floating sulfur and was pale turquoise in color. No lake temperature measurements were made but the entire surface steamed slightly. In contrast to a previous visit in March 1994, the lake level seemed significantly higher, although the amount has yet to be quantified from photographic records; zones of bubbling (previously several meters across) were absent.

Fumaroles on the crater's inner SE wall were quite active and fumed noiselessly. Gas plumes, clearly visible from the volcano's N flank, rose up to 100 m above the crater before being blown by the wind. Small, steam-rich fumaroles adjacent to concentric fractures surrounded the crater, typically near the 1,640 m contour. These fumaroles were also active last year.

At least two other noteworthy fumaroles, expelling steam and sulfurous gases, sit on the N flank (along the valley called Quebrada Azumicrorada at around 1,200- and 1,300-m elevation). In clear weather, these fumaroles are visible from local villages and residents stated that they had been active for the past several years.

Information Contacts: Erick Fernandez, Vilma Barboza, and Jorge Barquero, Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica; Gerardo J. Soto, Oficina de Sismologia y Vulcanologia del Arenal y Miravalles: OSIVAM; Instituto Costarricense de Electricidad (ICE), Apartado 10032-1000, San José, Costa Rica; Jean-Philippe Rancon, BRGM, Orleans, France (presently at USGS Cascades Volcano Observatory, 5400 MacArthur Blvd., Vancouver, WA 98661-7095 USA); Georges Boudon, Observatoires Volcanologiques, Institut de Physique du Globe de Paris, 4 Place Jussieu, 75252 Paris 05, France.

09/1995 (BGVN 20:09) Seismic activity continues at a rate of tens of events per month

The seismic receiver at the remote Rincón de la Vieja volcanic complex (RIN3) is located 5 km SW of the active crater. During August it registered 42 events at frequencies below 1.5 Hz; during September, 28 events with frequencies below 2.5 Hz.

Information Contacts: E. Fernandez, E. Duarte, R. Sáenz, W. Jimenez, and V. Barboza, Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica.

10/1995 (BGVN 20:10) New eruption; lahars damage a bridge and lead to evacuations

A new phreatomagmatic eruption followed three months of declining seismicity. During 1995 the number of local earthquakes peaked in July and then progressively decreased (figure 10). Prior to the eruption, during October, OVSICORI-UNA reported that park rangers who ascended to the main summit saw increased degassing and noted the appearance of fumaroles along cracks at the E and NE crater margins. Rangers described the crater lake's color as green and the smell as strong and sulfurous.

Figure 10. The number of monthly earthquakes at Rincón de la Vieja volcanic complex recorded 5 km SW of the active crater (station RIN3), January-October 1995. The seismic system failed to operate on 29 October; the three events recorded during the rest of the month were all of low frequency (<2.5 Hz). Courtesy of OVSICORI-UNA.

ICE described the eruption as phreatomagmatic, beginning at 1504 on 6 November, and climaxing on 8 November with 25 explosions. They noted the ash-bearing and steam-rich columns rose to 1 and 4 km, respectively, above the crater. Ash blew WSW; medium- to fine-grained ash reached up to 30 km from the volcano (Santa Rosa National Park).

According to ICE, on 9 November the eruption entered a steam-rich phase. Columns typically rose 200 m, but sometimes as much as 1.5 km after some steam explosions.

During the course of the eruption, ballistic ejecta were thrown over a zone extending to ~1 km N. Ejecta formed lahars that followed two key rivers (Penjamo and Azul rivers) and their tributaries. Heavy rains beginning on 10 and continuing on 11 November triggered secondary lahars and associated floods; a bridge 7 km N of the crater (Penjamo bridge) was damaged but not destroyed, interrupting traffic flow. During this episode, lahars along a tributary of the Penjamo river produced a gully 8-m deep and 25-m wide, isolating some inhabitants.

Initial inspections of ash and the lahar matrix indicated that they mainly consisted of hydrothermally altered fragments, lake-sediment mud, and vesiculated glassy andesite fragments.

Some residents living near the volcano were evacuated to a safe village 9 km NW of the crater. News reports on 8 November by both Associated Press and Deutsche Presse-Agentur stated that about 100 families were evacuated. Two days later Enrique Coen reported relocation of 300 families.

Information Contacts: E. Fernandez, E. Duarte, and V. Barboza, Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica; G.J. Soto, Oficina de Sismologia y Vulcanologia del Arenal y Miravalles: OSIVAM, Instituto Costarricense de Electricidad (ICE), Apartado 10032-1000, San José, Costa Rica; Enrique Coen, Departamento de Fisica, University Nacional, Heredia, Costa Rica; Associated Press; Deutsche Presse-Agentur.

12/1995 (BGVN 20:11) Additional details about the 6-10 November eruption

An eruption on 6 November 1995 followed increases in fumarolic activity and a several-month long increase in local earthquakes and tremor (figures 11 and 12). Park rangers who visited the summit at the start of October noted increased fumarolic activity and witnessed landslides down the main crater's walls. Strong sulfur smells were noted W-SW of the volcano on multiple occasions in the days prior to 6 November (figure 13).

Figure 11. Rincón de la Vieja's monthly totals for tremor and low-frequency seismicity, January-September 1995. Courtesy of OVSICORI-UNA.
Figure 12. Rincón de la Vieja's seismicity, 1-13 November 1995. An eruption began on 6 November. Courtesy of OVSICORI-UNA.
Figure 13. Map of NW Costa Rica showing key features associated with Rincón de la Vieja's 6 November 1995 eruption. Courtesy of OVSICORI-UNA.

The seismic receiver (RIN3) sits 5 km SW of the active crater. Although the OVSCICORI-UNA seismic system failed on 29 October (and possibly other times during the month), it functioned reliably again after the 31st. Low-frequency events gradually increased during 1-6 November (figure 12), followed by a modest decline. High-frequency events were only registered after 3 November. Tremor was absent prior to the 6 November eruption.

OVSCICORI reported that the first phase of the eruption consisted of vapor with subordinate ash in a discharge lasting 2 minutes. Later, vigorous fumarolic activity led to many hours of constant tremor. Only two more clear eruptions followed in the initial 17 hours of venting, but others followed in subsequent days. The eruption climaxed on the morning of the 8th, when columns reached 3.5 km altitude. Fine ash blew W and NW; larger blocks and tephra were confined to within ~1 km and the area of heavy ashfall reached ~5 km away (figure 13).

During some phases of the eruption, lahars flowed down the Azul and Penjamo rivers and an interfluvial ravine called the Quebrada Azumicrorada (figure 13). Upper reaches of these drainages sustained up to 6 m of erosion. Lahars on the 7th were cooler and more water-rich than those on the 8th. In addition to previously reported damage, on 8 November lahars shut down some communications systems.

At 0900 and 1130 on 8 November OVSICORI scientists visited the summit area and saw impact craters as large as 2 m in diameter; the craters were produced by 0.5-1.0 m diameter blocks, some of which were still warm to the touch. The scientists also saw ongoing phreatic eruptions escaping from a vent adjacent to the crater lake.

At 0411 on the 9th a shock wave was felt 25 km SE in the city of Liberia; the related outburst was seen from the N flank, where residents witnessed incandescent block ejections.

Amplitudes on the seismic recorders regularly peaked at over 30 mm on 6-9 November. The highest amplitudes, on 7-9 November, reached nearly 60 mm. Amplitudes decreased the morning of 9 November; following the eruption (10-14 November) amplitudes generally remained under 10 mm with infrequent spikes to ~20 mm and a few rare spikes to 30 mm. Tremor decreased by an order of magnitude on 10 November and it dropped to <1 hour/day on 13 November.

During fieldwork in early December, G. Soto (ICE) and G. Boudon (IPG) inspected the near-source region. For a radial distance of ~1 km from the crater they saw a deposit consisting of muddy ash, lapilli, and blocks. These reached 40 cm thick on the crater's southern outer rim at a point 150 m from the inner rim. The deposit's thickness and grain size decreased rapidly with distance, such that at 600 m SW of the crater the deposit was only 7 cm thick. The deposit's basal zone was enriched in fine grained, muddy-looking material, but throughout the deposit there occurred lustrous black juvenile clasts. Over ~1 km2 of the upper surface of the deposit, there lay a blanket consisting of (a) dense, quenched blocks, (b) breadcrust bombs with notably vesicular cores, and (c) some highly vesiculated fragments. On 8 December at points 5 and 8 km from the summit, the Penjama and Blanco rivers, respectively, still ran milky and were slightly acidic in taste. That same day, the scientists saw only fumarolic activity. Although scientists looked for a lake in the depths of the crater, they failed to gain a clear view there.

Reference. Boudon, G., Rancon J.-P., Kieffer, G., Soto, G.J., Traineau, H., and Rossignol, J.-C., 1995, Estilio eruptivo actual del Volcan Rincón de la Vieja: evidencias de las productos de las erupciones de 1966-70 y 1991-92: Rothschildia, 2 (2): 10-13, Area de conservacion de Guanacaste, Costa Rica.

Information Contacts: E. Fernandez, E. Duarte, R. Sáenz, W. Jimenez, and V. Barboza, Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica; Georges Boudon, Institut de Physique du Globe de Paris, 4, Place Jussieu, 75252, Paris Cedex 05, France.

01/1996 (BGVN 21:01) Eruption on 11-13 November followed by decreasing seismicity

The eruption that began on [6] November had ended by 13 November (BGVN 20:11/12), yet somewhat elevated seismicity (4 events/day) prevailed through late November. Although the seismic system (RIN3, 5 km SW of the active crater) later failed (all or partly inoperative, 3 December-3 January), it received low-frequency events during most of 1-10 December at the rate of 1-3 events/day, and on 6 December it recorded eight events. During January, RIN3 registered near background levels of seismicity: 8 events/month, consisting of two at low frequencies and six at high frequencies.

Information Contacts: Rodolfo Van der Laat, Vilma Barboza, Erick Fernández, Jorge Barquero, Franklin de Obaldia, Tomás Marino, and Rodrigo Sáenz, Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica.

03/1996 (BGVN 21:03) Mild seismicity continues in February

Several small-to-moderate eruptions took place in early November 1995 (BGVN 20:10 and 20:11/12). Mild seismicity continued after the eruption; during February seismic station RIN3, located 5 km SW of the active crater, registered seven microseisms (six low-frequency, one high-frequency). These microseisms were only detected locally.

Information Contacts: Erick Fernández, Elicer Duarte, Vilma Barboza, Rodolfo Van der Laat, and Enrique Hernandez, Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica; Gerardo J. Soto, Oficina de Sismolog¡a y Vulcanolog¡a, Departamento de Geolog¡a, Instituto Costarricense de Electricidad (ICE), Apartado 10032-1000, San José, Costa Rica.

05/1996 (BGVN 21:05) Seven minor seismic events

During May seismic station RIN3 registered a total of seven events: two of high frequency and five of low frequency.

Information Contacts: Erick Fernández, Elicer Duarte, Vilma Barboza, Rodolfo Van der Laat, and Enrique Hernandez, Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica.

06/1996 (BGVN 21:06) Six-fold seismic increase over previous months in 1996

The local seismic station (RIN3, located 5 km SW of the active crater) registered a total of 50 events, a 6-fold increase over any previous month in 1996. These events were only detected at this seismic station.

Information Contacts: Erick Fernández, Elicer Duarte, Vilma Barboza, Rodolfo Van der Laat, and Enrique Hernandez, Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica.

08/1996 (BGVN 21:08) Small local earthquakes

Seismic station RIN3, located 5 km SW of the active crater, detected local microseisms. During July there were 27 events; during August, 16 events. For comparison, the near background levels of seismicity during January 1996 consisted of 8 events/month.

Information Contacts: E. Fernández, E. Duarte, V. Barboza, R. Van der Laat, E. Hernandez, M. Martinez, and R. Sáenz, Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica.

01/1997 (BGVN 22:01) Sulfur-bearing steam, mass wasting, and acid rain in September

A visit to the crater during September 1996 revealed vegetation killed by the phreatic eruption of November 1995 (BGVN 20:10 and 20:11/12), by mass wasting in its aftermath, and by continued acidic rainfall. Although some plants were beginning to return, most suffered visible damage such as scalded leaves. The crater area continued to smell of sulfur and the loud noise of escaping steam could be heard from the crater's margin.

Information Contacts: E. Fernández, E. Duarte, V. Barboza, R. Van der Laat, E. Hernandez, M. Martinez, and R. Sáenz, Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica.

05/1997 (BGVN 22:05) Conspicuous fumaroles and plumes persist

During April, fumarolic activity remained in the E and S parts of the main crater. In the latter location, escaping gases hissed like a pressure cooker and were audible from the crater rim. Gas columns rose up to 200 m high. Adjacent to the crater, visitors smelled sulfur gases and their throats, eyes, and skin became irritated. Some of the plants damaged during November 1995 showed new signs of recovery. Although the seismic station (RIN3, located 5 km SW of the active crater) remained out of service during May, earthquake counts numbered five events in December 1996 and 24 in January 1997.

Information Contacts: E. Fernandez, R. Van der Laat, F. de Obaldia, T. Marino, V. Barboza, W. Jimenez, R. Sáenz, E. Duarte, M. Martinez, E. Hernandez, and F. Vega, Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica.

09/1997 (BGVN 22:09) Variable but modest seismicity during June-September 1997

OVSCORI-UNA reported that over the last several months earthquake totals were as follows: June, 2; July, 43 (including 24 microseisms); August, 20; and September, 100 (including 45 microseisms). Gerardo Soto (OSIVAM) spoke with park rangers who said there had been several rockslides along the crater's NE and N inner slopes during the first half of 1997. Some of these slides created small islands in the lake.

Information Contacts: E. Fernandez, R. Van der Laat, F. de Obaldia, T. Marino, V. Barboza, W. Jimenez, R. Sáenz, E. Duarte, M. Martinez, E. Hernandez, and F. Vega, Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica; G.J. Soto, Oficina de Sismologia y Vulcanologia del Arenal y Miravalles (OSIVAM), Instituto Costarricense de Electricidad (ICE), Apartado 10032-1000, San José, Costa Rica.

03/1998 (BGVN 23:03) Phreatic eruptions on 15-17 February thrust steam to 2 km

Beginning at 1428 on 15 February, Rincón de la Vieja volcano discharged phreatic eruptions from the main crater. Ten eruptions took place in the first 15 hours of activity; only two followed in the subsequent 13 hours. During the course of the outburst subsidiary fumarolic activity also became more vigorous; it remained elevated until 18 February.

During 15-17 February numerous steam plumes rose hundreds of meters above the volcano. On 17 February one outburst sent a steam plume to a height of 2 km above the crater. This plume was seen by residents on the N and NE flanks of the volcano. A dozen eruptions around this time were small and lacked associated mudflows. An exception, at 0514 on 16 February, produced a modest mudflow that traveled about 9 km/hour and left a capping deposit of mud 30-cm thick in the upper reaches of the Pénjamo and Azul rivers. Rivers had been low in the region, attributed to the El Niño phenomena, with the result that the mudflow was relatively dry. The mudflow had a large impact on local fish and other stream organisms. Sediment from the mudflow was found 12.3 km from the main crater.

Inspecting the 16 February deposit near the summit on 1 March, scientists inferred from the scorching, burning, and other damage to vegetation on the NE flanks that there must have been several smaller eruptions around that time as well. Mudflows failed to develop due to the paucity of surface water in local drainages.

The 1 March visit also revealed the lake's temperature, 48°C, its color, light gray, the presence of suspended sulfur in the lake, and a haze of condensed gases above the lake. An outgassing fumarole on the SW wall made loud hissing noises (similar to gases exiting a high pressure valve) audible from the crater's rim. Columns of gas rose about 200 m above the crater before being blown E. Those inspecting the scene noted strong sulfurous odors, and experienced irritated skin and eyes. The material erupted was uniformly fine- to medium-grained, lacking either bombs, blocks, or impact craters. This contrasted with deposits left by previous eruptions in 1991 and 1995.

The local seismic station (RIN3) lies 5 km SW of the active crater. The station registered microearthquakes as follows: during January, 18 (including 3 of high frequency and 9 of low frequency); during February, 48 (including 1 of high frequency, 21 of low frequency); during March, 7. In assessing their records of the 48 February microearthquakes, seismologists recognized 20 eruptions including 11 comparatively high-intensity phreatic eruptions mainly registered on 15-18 February. Banded tremor occurred on 15 and 16 February during the main eruptive interval; the tremor prevailed for a total of ~6.5 hours. Low in frequency, the tremor had amplitudes that ranged between 1.0 and 37 mm. The larger amplitude registered during the eruption's initial phase, at 1428 on 15 February. Tremor amplitudes later declined to the 1-4 mm range. As with the 1991 and 1995 eruptions, seismic precursors were absent.

Information Contacts: E. Fernandez, V. Barboza, R. Van der Laat, R. Sáenz, E. Duarte, E. Malavassi, T. Marino, M. Martinez, and E. Hernandez, Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica; Mauricio Mora Fernandez, Sección de Sismologia, Vulcanologia y Exploración Geofisica, Escuela Centroamericana de Geología, Universidad de Costa Rica, P.O. Box 35-2060, San José, Costa Rica (Email: mmmora@cariari.ucr.ac.cr).

06/1998 (BGVN 23:06) Non-eruptive and relatively quiet seismically during April-June

The volcano has been relatively quiet since phreatic eruptions on 15-17 February sent plumes to 2 km. During April, May, and June the local seismic system registered 3, 27, and 17 events, respectively. The April seismic events were of unspecified type. The May seismic events included eight of high frequency; in addition, one hour of low-frequency tremor took place. Seismicity during June included some low-frequency events.

Information Contacts: E. Fernandez, V. Barboza, E. Duarte, R. Sáenz, E. Malavassi, M. Martinez, and Rodolfo Van der Laat, Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.una.ac.cr/ovsi/).

06/1999 (BGVN 24:06) 1.5-year record of seismicity and eruptions through May 1999

Seismicity during 17 months through April 1999 (figure 14) showed pronounced peaks at over 100 events/month in one parameter, microseisms, during September- October 1998. Otherwise, relative quiet prevailed; microseisms, high-frequency, and low-frequency events all generally took place fewer than 20 times/month. Tremor was nearly absent during roughly half the months of 1998 and in 1999 during January, February, and April. Months with 2-10 hours of tremor included February, August, September 1998 and March and May 1999.

Figure 14. Selected seismic parameters at Rincón de la Vieja during January 1998-May 1999. The arrows indicate months with detected eruptions (mainly in February 1998, a month with ~10; the other indicated months with fewer than 2). Courtesy of OVSICORI-UNA.

In March, fumarolic activity continued on the NE, S, and SW walls of the main crater. The lake had a gray color and contained suspended particles of sulfur. The temperature of the lake was 35.5°C.

During May, the main crater's N-flank fumarolic activity fluctuated in temperature between 68°C and 92°C. The lake in the crater was light blue with particles of sulfur, and a temperature of 37°C. On the S and N walls, there were columns of gases that irritated eyes and skin.

Information Contacts: E. Fernandez, V. Barboza, E. Duarte, R. Sáenz, E. Malavassi, M. Martinez, and R. Van der Laat, T. Marino, and E. Hernandez; Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.una.ac.cr/ovsi/); Wendy Perez Fernandez, Seccion de Seismologia, Vulcanologia y Exploracion Geofisica, Escuela Centroamericana de Geologia, Universidad de Costa Rica, POB 35-2060, San José, Costa Rica (Email: wendyp@cariari.ucr.ac.cr).

03/2000 (BGVN 25:03) Non-eruptive through November 1999 but with ongoing tremor

The noisy escape of fumarolic gases continued at Rincón de la Vieja during June-November 1999. A summary of monitoring data appears in table 7. During August the crater floor became covered with a shallow ephemeral lake, covering the fumaroles there. Plumes then rose less than 100 m above their fumarolic sources. The active crater lake, with a sky-blue color, had a temperature of 36°C; the maximum measured fumarole temperature was 70°C.

Table 7. Geotechnical data at Rincón de la Vieja, July-November 1999. Seismic data recorded at station RIN3, 5 km SW of the active crater, includes microseisms who's amplitudes were under 5 mm, and those volcano-tectonic (VT) earthquakes with S minus P arrival times under 1.5 seconds (i.e. focused near the volcano). The reported tremor durations were sums of discontinuous segments, and were low-frequency (below 2 Hz). Courtesy of OVSICORI-UNA.

    Month      Low-frequency     Microseism         VT         Tremor
                earthquake    (amplitude <5 mm)  earthquake   duration

    Jul 1999        9                 2           2 hrs         NR
    Aug 1999        8                 1             14        0.5 hrs
    Sep 1999        5                21              4        0.75 hrs
    Oct 1999        4                12              4        6.5 hrs
    Nov 1999        6                 5              0        2 hrs

Information Contacts: E. Fernandez, E. Duarte, V. Barboza, R. Sáenz, E. Malavassi, R. Van der Laat, T. Marino, J. Barquero, and E. Hernández, Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.una.ac.cr/ovsi/).

11/2001 (BGVN 26:11) Fumarolically active through August 2001

During March 2000 through at least August 2001, fumarolic and seismic activity continued at Rincón de la Vieja. Fumarolic gases often irritated the eyes, skin, and throat.

On 1 March 2000 the crater lake was blue, with sulfur particles in suspension, a constant surge, and a temperature of 37°C. Compared to a visit in September 1999, the level of the lake was higher and the bubbling in the SW part had ended. The fumaroles on the NE (91°C) and SW walls were no longer steaming. The fumaroles on the NE flank (89°C) were steaming slightly. The edge of the crater displayed concentric 50-m-long and 40-cm-wide cracks.

During October 2000, the lake was gray with a high water level, sulfur particles floating on the surface, evaporation, and a temperature of 44°C. Fumarolic activity was observed in the SW and N wall of the main crater. The fumarolic area of the N flank (60°C) was steaming slightly, and sublimate deposition occurred.

During July 2001, OVSICORI-UNA reported that the level of the lake had descended ~2 m since mid-March. The lake was gray in color with sulfur particles floating on the surface; vigorous evaporation made observation of its bottom difficult, and its temperature stood at 58°C. In the SW wall there were small areas sliding towards the lake, and a new noisy fumarole appeared on the S wall. The fumaroles on the NE and SW walls remained active, producing gas columns that reached up to 300 m. The columns, often visible from the N and NW flanks, were blown by predominant winds towards the W and SW flanks. Low-frequency events and microearthquakes increased during June and August 2001. A summary of earthquakes at Rincón de la Vieja appears in table 1.

Table 1. Summary of earthquakes at Rincón de la Vieja during May 2000 to August 2001, registered by a seismograph at a station located 5 km SW of the main crater. The reported earthquakes include microseisms with amplitudes under 5 mm. The reported tremor durations were sums of discontinuous segments and were of low frequency (below 2 Hz). Missing months indicate that no data were available at the time of report preparation. Courtesy of OVSICORI-UNA.

    Month      LF   HF   Micro-        Tremor         VT    Total
                         earthquakes   duration

    May 2000    3    1      25         105 minutes    --     29
    Aug 2000    8   --      21          30 minutes    --     29
    Sep 2000    7   --      --         210 minutes    11     18
    Mar 2001    2   --       5          --            --      7
    May 2001    5   --       2          --            --      7
    Jun 2001   12   --      20          --             1     33
    Aug 2001   35   --      50          --            --     85

General References. Barquero, J., and others, 1978-1986, Estado de los Volcanes de Costa Rica (15 annual or semi-annual reports): Boletín de Vulcanología, nos. 2-13 and 15-17.

Garcia, M.O., and Malavassi, E. (eds.), 1983, Memoir, USA-Costa Rica Joint Seminar in Volcanology, San José, January 1982: Universidad Nacional, Heredia, 155 p. (18 papers).

Information Contacts: Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.una.ac.cr/ovsi/).

10/2007 (BGVN 32:10) Continued fumarolic activity; sulfur floating in the lake

During September 2006 through at least May 2007, low-level fumarolic and seismic activity continued at Rincón de la Vieja. At the edge of the crater, Fumarolic gases often irritated the eyes, skin, and throat.

During September 2006, the level of the lake was high, with convection cells and particles of sulfur floating on the surface. The lake displayed yellow color with minor evaporation and a temperature of 39°C. Fumarolic activity was occurring in the S wall and SW part of the crater. Columns of gases rose above the edge of the crater and were carried by the predominant winds toward the W and SW. The fumaroles on the N side produced only low-level emissions.

By April and May 2007, the level of the lake had descended some 50 cm with respect to September 2006. The lake color turned to gray with minor evaporation. In the S, there were particles of sulfur floating on the surface and a temperature of 45°C. The fumarolic activity on the SW wall displayed low levels of gas emission and rich sulfur depositions. The fumaroles of the N side were inactive.

Information Contacts: E. Fernández, E. Duarte, R. Van der Laat, M. Martinez, W. Sáenz, V. Barboza, Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/).

07/2008 (BGVN 33:07) Tremor durations from minutes to over an hour during June-April 2008

Activity at Rincón de la Vieja was last reviewed in May 2007 (BGVN 32:10), when low-level fumarolic activity was noted. During June 2007, the seismographic station 5 km to the SW of the crater registered seven low-frequency earthquakes and three low-frequency tremors. The first tremor occurred on 12 June and lasted 2 hours and eight minutes; the second and third occurred on 27 and 28 June and they lasted 37 minutes and 38 minutes, respectively.

The July earthquake activity was consistent with June; 6 low frequency quakes were recorded. Again, tremor activity occurred on 28 and 29 July, the first lasted 35 minutes and the second lasted 17 minutes. Little activity was noted during August and September, and October activity consisted only of tremors. On 23 October, the tremor lasted 37 minutes, and on 24 October it lasted 25 minutes.

No significant seismicity was recorded during the first three weeks of November. The seismic recording instrument went out of service from 22 November through December and January.

During February, 2008, 44 low-frequency earthquakes were registered in two groups; the first on 6 and 7 February and the second between 17 and 23 February.

Technical difficulties in March precluded a complete record of seismic activity; however, when recording was available, 116 low frequency earthquakes were noted.

Technical problems persisted in April, however during the first part of the month there was a low-frequency earthquake and 1.16 hours of tremor. Two deep earthquakes were also noted; the first registering M 3.5 at a depth of 11 km and the second M 2.9 at a 25 km depth.

Information Contacts: E. Fernández, E. Duarte, R. Van der Laat, M. Martinez, W. Sáenz, V. Barboza, Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/).

04/2011 (BGVN 36:04) Fumarolically active but non-eruptive through January 2011

Low-frequency earthquakes and tremor were reported at Rincón de la Vieja during the first half of 2008 (BGVN 33:07). Since then, Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA) had issued intermittent reports of activity through January 2011. Those reports are summarized in the following sections, with much of the discussion centered around fumaroles and behavior of the geothermally warmed lake in the active crater. Occasional, typically small phreatic eruptions had occurred here in past years, for example in the 1990s (eg., BGVN 21:02, 21:03, 22:01, and 23:03) but were absent in the current reporting interval (last half of 2008 through January 2011).

August 2008. OVSICORI-UNA reported that the level of the lake was at a high level, with a bluish color, generated convection cells with evaporation, and had sulfur particles visible on it's surface. Sulfur deposition and fumarolic activity continued along the SW wall.

March 2009. In mid-March 2009, scientists visited the S and SW flank, collected samples, and noted some temperatures of 75-78°C. Because the visit occurred during the dry season, most areas encountered were dry. The scientists examined an area of acidification to the W of Von Seebach crater, ~3 km SW of the active crater. Strong winds common in that direction sometimes carried volcanic gases. Consequently, most of this narrow expanse only contained patches of grassland and shrubs that barely covered the rocky surface.

October 2009. OVSICORI-UNA reported that seismographic station RIN3, located ~5 km SW of the main crater, registered volcano-tectonic events and tremor lasting for minutes.

Weak ongoing fumarolic activity during 2010 through January 2011. OVSICORI-UNA reported that the level of the crater lake remained high during 2010, with constant evaporation. Geochemical, seismic, and deformation data did not show significant changes in physico-chemical parameters during 2010. The changing color of the lake, from blue to gray, was attributed to intense rains and fumarolic activity in the crater.

Later reporting. Reports during 2010 through at least January 2011 described fumarolic activity along the S and SW walls of the crater, with sulfur deposition and moderate gas discharge. The lake remained a gray color, with sulfur particles in suspension. Figure 15 shows a photo taken in April of the crater looking at the SW wall with fumarolic activity along with sulfur deposition. In April 2010, OVSICORI-UNA reported that the temperature of the lake was 49°C. A fumarole sometimes seen active along the N flank had stopped discharging gas.

Figure 15. Photo of the active crater lake of Rincón de la Vieja on 29 April 2010 showing yellow sulfur deposits and fumarolic activity along the SW wall of the crater. This kind of activity was typical throughout the reporting interval (last half of 2008 through January 2011). Photo by E. Fernandez, OVSICORI-UNA.

OVSICORI-UNA reported that 2010 was unusual in that four domestic volcanoes were active: Arenal, Poás, Turrialba, and Rincón de la Vieja. Irazú was comparatively inactive (see separate report in this issue of the Bulletin).

Information Contacts: E. Fernández, W. Sáenz, E. Duarte, M. Martínez, S. Miranda, F. Robichaud, T. Marino, M. Villegas, and J. Barquero, Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/).

Rincón de la Vieja, the largest volcano in NW Costa Rica, is a remote volcanic complex in the Guanacaste Range. The volcano consists of an elongated, arcuate NW-SE-trending ridge that was constructed within the 15-km-wide early Pleistocene Guachipelín caldera, whose rim is exposed on the south side. Sometimes known as the "Colossus of Guanacaste," it has an estimated volume of 130 cu km and contains at least nine major eruptive centers. Activity has migrated to the SE, where the youngest-looking craters are located. The twin cone of 1916-m-high Santa María volcano, the highest peak of the complex, is located at the eastern end of a smaller, 5-km-wide caldera and has a 500-m-wide crater. A plinian eruption producing the 0.25 cu km Río Blanca tephra about 3500 years ago was the last major magmatic eruption. All subsequent eruptions, including numerous historical eruptions possibly dating back to the 16th century, have been from the prominent crater containing a 500-m-wide acid lake (known as the Active Crater) located ENE of Von Seebach crater.

Summary of Holocene eruption dates and Volcanic Explosivity Indices (VEI).

Start Date Stop Date Eruption Certainty VEI Evidence Activity Area or Unit
2014 Sep 17 2014 Sep 20 Confirmed 1 Historical Observations Crater lake
2012 Feb 19 2012 Apr 14 Confirmed 1 Historical Observations Crater lake
2011 Aug 15 ± 3 days 2011 Sep 26 (?) Confirmed 1 Historical Observations Crater lake
1998 Feb 15 1998 Sep Confirmed 2 Historical Observations
1995 Nov 6 1995 Nov 13 Confirmed 2 Historical Observations
1991 May 7 1992 Sep Confirmed 2 Historical Observations
1987 Apr 1 1987 Apr 1 Confirmed 1 Historical Observations
1986 Dec 31 1986 Dec 31 Confirmed 1 Historical Observations
1985 Sep 1986 Apr Confirmed 1 Historical Observations
1984 Mar 31 1984 Apr Confirmed 2 Historical Observations
1983 Feb 6 1983 Feb 21 Confirmed 1 Historical Observations
1970 Aug 14 1970 Aug 15 Confirmed 1 Historical Observations
1969 Sep 20 1969 Oct 16 Confirmed 2 Historical Observations
1969 Apr 22 1969 May Confirmed 2 Historical Observations
1966 Nov 6 (?) 1967 Dec Confirmed 3 Historical Observations
1922 Apr 11 (in or before) 1922 Jun 4 Confirmed 2 Historical Observations
[ 1917 ] [ Unknown ] Uncertain    
1912 Jun 14 Unknown Confirmed 3 Historical Observations
[ 1902 Jun 22 ] [ Unknown ] Uncertain 2  
1854 1863 Aug Confirmed 2 Historical Observations
1853 Unknown Confirmed 2 Historical Observations
[ 1851 ] [ Unknown ] Uncertain    
1849 Unknown Confirmed 2 Unknown Volcano Uncertain: more likely Rincón de la Vieja than Orosí
1844 May Unknown Confirmed 2 Unknown Volcano Uncertain: more likely Rincón de la Vieja than Orosí
1765 Unknown Confirmed 2 Historical Observations
[ 1529 ] [ Unknown ] Uncertain    
0430 ± 100 years Unknown Confirmed   Radiocarbon (corrected)
1820 BCE ± 150 years Unknown Confirmed 4 Radiocarbon (corrected) Río Blanco tephra

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.


Cones

Feature Name Feature Type Elevation Latitude Longitude
Chato, Cerro Cone 1130 m
Santa María Cone 1916 m 10° 48' 43" N 85° 19' 16" W
Von Seebach
    Braun
Cone 1895 m 10° 50' 0" N 85° 21' 11" W

Craters

Feature Name Feature Type Elevation Latitude Longitude
Active Crater Crater 1740 m 10° 50' 0" N 85° 20' 0" W
Guachipelín Pleistocene caldera

Domes

Feature Name Feature Type Elevation Latitude Longitude
Cañas Dulces Dome 655 m 10° 45' 0" N 85° 26' 0" W
Fortuna, Cerro Dome 479 m 10° 49' 0" N 85° 27' 54" W
Gallo, Cerro Dome 764 m
Gongora, Cerro Dome 768 m 10° 45' 54" N 85° 24' 54" W
San Roque, Cerro Dome 545 m 10° 46' 26" N 85° 27' 47" W
San Vicente Dome 608 m

Thermal

Feature Name Feature Type Elevation Latitude Longitude
Aguas Termales Thermal
Azufrales Thermal
Boriquén Thermal
Pailas, Las Thermal
Sitio Hornillas Thermal
Volcancitos Thermal
The SW flank of Rincón de la Vieja volcano contains an unusual broad triangular area almost entirely devoid of vegetation. This so-called "dead zone" has resulted from active eruptions and volcanically derived acid rain. Steady trade winds from the NNE distribute acidic vapors rising from Active Crater to the SW. These factors have created unusual exposures revealing the stratigraphy of the volcano.

Photo by William Melson, 1986 (Smithsonian Institution).
An ash-laden eruption column rises above Rincón de la Vieja volcano on June 4, 1922. About two months earlier (on April 11) evidence of a recent large eruption had been observed. After the explosive eruption of June 4, no further eruptive activity was recorded until 1966, when eruptions began occurring more frequently.

Photo by José Tristan, 1922 (courtesy of Jorge Barquero).
Laguna de Fria (center) is seen here from the west, along a ridge crest near Active Crater. Laguna de Fria (also known as Laguna los Jilgueros) does not lie within a volcanic crater, but was formed when meteoric waters accumulated in a depression between overlapping cones of the Rincón de la Vieja complex. The peak at the upper right is Rincón de la Vieja cone. It is one of many peaks forming the elongated summit ridge of the Rincón de la Vieja volcanic complex, and its forested summit contains a roughly 700-m-wide crater.

Photo by Cindy Stine, 1989 (U.S. Geological Survey).
The walls of Cráter Activo (Active Crater) expose thick sequences of oxidized and hydrothermally altered pyroclastic deposits and light-colored lava flows. Many sublacustral eruptions from Active Crater have originated from vents beneath the acidic crater lake seen at the lower right.

Photo by Guillermo Alvarado (Instituto Costarricense de Electricidad).
The elongated profile of the Rincón de la Vieja massif is less prominent in this view from the west across the coastal plain. The volcanic massif is the largest in NW Costa Rica. It has an estimated volume of 130 cu km and is sometimes referred to as the "Colossus of Guanacaste." A rhyolitic ignimbrite, the Liberia Tuff, originated from Rincón de la Vieja during the early Pleistocene. It covered an area of 3500-4000 sq km, blanketing wide areas of the Pacific coastal plain south and west of the volcano.

Photo by Guillermo Alvarado (Instituto Costarricense de Electricidad).
The rim of Active Crater is highest on the SW side and drops rapidly on the NW side. The 700-m-wide crater contains an acidic lake that is periodically partially ejected by explosive eruptions and therefore varies in depth. Trade winds from the ENE distribute acid fumarolic plumes from the Active Crater to the SW, destroying vegetation. Water geochemistry studies indicate that the crater lake water is leaking through the edifice into the north flank drainages.

Photo by Guillermo Alvarado (Instituto Costarricense de Electricidad).
Deposits of the Liberia Tuff are exposed in steep-walled gullies SW of the volcano. The rhyolitic ignimbrite was erupted about 1.6 million years ago and blanketed an area of 3500-4000 sq km. The Liberia Tuff differs from other ignimbrite deposits in NW Costa Rica in containing a large amount of biotite phenocrysts. Eruption of the 25 cu km ignimbrite was associated with formation of the 15-km-wide Guachipelín caldera, inside which the modern Rincón de la Vieja massif was constructed.

Photo by Lee Siebert, 1998 (Smithsonian Institution).
Cerro San Roque (left), Cerro Gongora (center), and Cerro Canas Dulces (right), seen here from the west along the Pan-American highway, are rhyodacitic lava domes just outside the Guachipelín caldera. The domes were formed prior to eruption of the Liberia Tuff and formation of the caldera about 1.6 million years ago.

Photo by Lee Siebert, 1998 (Smithsonian Institution).
Fumarolic plumes issue from vents at the margin of a pool at the Aguas Termales thermal area on the southern base of Rincón de la Vieja volcano. A popular recreational trail in Rincón de la Vieja National Park makes a circuit through the mudpots and fumaroles of the geothermal area.

Photo by Paul Kimberly, 1988 (Smithsonian Institution).
Steam rises from active bubbling mudpots at the Aguas Termales thermal area, one of several at the southern base of the Rincón de la Vieja massif in the national park of the same name.

Photo by Paul Kimberly, 1998 (Smithsonian Institution).
The Aguas Termales geothermal field at the southern base of Rincón de la Vieja volcano contains active mudpots. Several geothermal areas occur along a NW-trending lineation at the base of the volcano. Soil mercury studies delineate a fault parallel to the volcanic front that connects the geothermal sites.

Photo by Lee Siebert, 1998 (Smithsonian Institution).
This aerial photo from the east overlooks the summit cone complex of the Rincón de la Vieja volcanic massif, the centerpiece of the 14,083-hectare Rincón de la Vieja National Park. The turquoise-colored lake of the Active Crater lies at the right center, with the dark-colored Laguna Fria at the lower left. The arcuate, forested ridge at the lower left is the rim of Rincón de la Vieja cone itself. Erosional gullies cut the tephra-mantled slopes of the Active Crater and Von Seebach cone at the upper left.

Photo by Federico Chavarria Kopper, 1995 (courtesy of Eduardo Malavassi, OVSICORI-UNA).
The turquoise-colored crater lake of the Cráter Activo of Rincón de la Vieja is seen here on April 2, 1998 from its eastern rim during a quiet period of the 1998 eruption. The eruption began with phreatic explosions during February 15-18 that produced steam plumes up to 2 km above the crater lake and scorched vegetation on the NE side of the crater. On February 16 a mudflow traveled up to 12 km down the Penjamo and Azul rivers. Twenty explosions were recognized from seismic records, and additional explosions were recorded in May, June, and September.

Photo by José Enrique Valverde Sanábria, 1998 (courtesy of Eduardo Malavassi, OVSICORI-UNA).
A steam plume rises from Active Crater (Cráter Activo) of Rincón de la Vieja, seen here from the south. An acid crater lake fills the innermost of two nested craters of the historically active pyroclastic cone. Frequent historical eruptions and the production of acid rain have kept the flanks of the cone unvegetated. Remobilization of fresh ashfall deposits has led to mudflows down the Quebrada Azufrosa at the upper right.

Photo by Federico Chavarria Kopper, 1999.
Part of the complex summit region of Rincón de la Vieja, the largest volcano in NW Costa Rica, is seen here from the north. Steam rises from the lake-filled Cráter Activo at the left, ENE of the shallow 1895-m-high Von Seebach crater (upper right). Laguna Fria (upper left) is not a crater lake, but a freshwater lake that formed between overlapping cones of the summit complex, which extends east and west beyond the area of this photo. Frequent historical eruptions from Cráter Activo have left surrounding terrain unvegetated and scarred by erosional gullies.

Photo by Federico Chavarria Kopper, 1999.
This aerial photo from the north overlooks the summit cone complex of the Rincón de la Vieja volcanic massif, the largest volcano in NW Costa Rica. A steam plume rises from the acidic turquoise-colored lake of the Active Crater, and erosional gullies cut its tephra-mantled slopes. Dark-colored Laguna Fria beyond the Active Crater is a non-volcanic lake formed between the forested Rincón de la Vieja crater (middle left margin) and the ridge extending to Santa María cone at the upper left margin of the photo.

Photo by Federico Chavarria Kopper, 1996.
An aerial view from the north looks down on the acidic lake of the Active Crater. Layered pyroclastic deposits are exposed in its SW crater wall. The crater rim of forested Rincón de la Vieja cone is at the upper left, with the non-volcanic Jilgueros lake (also known as Laguna Fria) at the top center.

Photo by Eliecer Duarte (OVSICORI-UNA).
The barren slopes of Von Seebach cone at the upper right are a result not of its frequent eruptions, but of tephra and acidic gases blown downwind from the lake-filled Active Crater (left). Steady trade winds from the NNE distribute acidic vapors rising from Active Crater to the SW, creating the "Dead Zone" that extends down the SW flanks visible at the extreme upper right.

Photo by Eliecer Duarte (OVSICORI-UNA).
An unnamed eroded compound crater lies near the western margin of the Rincón de la Vieja volcanic massif in this aerial view from the SE. This roughly kilometer-wide crater lies about 2 km west of the Active Crater. Steep, closely spaced erosional valleys cutting the flanks of the 1700-m-high cone are prominent at the lower left. Rincón de la Vieja means "The Old Lady's Corner," an apparent reference to its isolated location.

Photo by Eliecer Duarte (OVSICORI-UNA).
Rincón de la Vieja National Park is host to more than 300 species of birds, including quetzals, toucanets, and eagles. Mammals include howler, spider, and white-faced monkeys, kinkajous, sloths, tapirs, tayras, cougars, and even jaguars. Barren slopes surround the Active Crater of the Rincón de la Vieja volcanic massif in this aerial view from the NE. Los Jilgueros lake is in the middle and the large forested inactive crater of Rincón de la Vieja behind it and to the left. Santa María volcano is in the far background.

Photo by Eliecer Duarte (OVSICORI-UNA).

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.

Alvarado G E, 1989. Los Volcanes de Costa Rica. San Jose, Costa Rica: Universidad Estatal a Distancia, 175 p.

Alvarado G E, 2000. Volcanes de Costa Rica: su geologia, historia y riqueza natural. San Jose, Costa Rica: EUNED, 269 p.

Alvarado G E, Vega E, Chaves J, Vasquez M, 2004. Los grandes deslizamientos (volcanicos y no volcanicos) de tip debris avalanche en Costa Rica. Rev Geol Amer Central, 30: 83-99.

Alvarado G, Acevedo A P, Monsalve M L, Espindola J M, Gomez D, Hall M, Naranjo J A, Pulgarin B, Raigosa J, Sigaran C, Van der Laat R, 1999. El desarrollo de la vulcanologia en Latinoamerica en el ultimo cuarto del siglo XX. Rev Geofis, 51: 185-241.

Alvarado-Induni G E, 2005. Costa Rica, Land of Volcanoes. San Jose, Costa Rica: EUNID, 306 p.

Barquero J, de Dios Segura J, 1983. La actividad del Volcan Rincon de la Vieja. Univ Nac Bol Vulc, 13: 5-10.

Barquero-H J, Saenz-R R, 1987. Aparatos volcanicos de Costa Rica. Heredia, Costa Rica: OVSICORI-UNA, 1:750,000 map and volcano list.

Boudon G, Rancon J-P, Kieffer G, Soto G J, Traineau H, Rossignol J-C, 1995. Estilo eruptivo actual del volcan Rincon de la Vieja: evidencias de los productos de las erupciones de 1966-70 y 1991-92. Rothschildia, 2(2): 10-13.

Boudon G, Rancon J-P, Kieffer G, Soto G J, Traineau H, Rossignol J-C, 1996. Les eruptions de 1966-1970 et 1991-92 du volcan Rincon de la Vieja, Costa Rica: exemple d'activite recurrente d'un systeme hydromagmatique. Compte Rendus Acad Sci Paris, Ser II, 332: 101-108.

Carr M J, 1984. Symmetrical and segmented variation of physical and geochemical characterisitics of the Central American volcanic front. J Volc Geotherm Res, 20: 231-252.

Carr M J, Chesner C A, Gemmell J B, 1986. Nuevos analisis de lavas y bombas del volcan Rincon de la Vieja, Costa Rica. Bol Vulc Univ Nac Costa Rica, 16: 23-26.

Chiesa S, Alvarado G E, Pecchio M, Corella M, Zanchi A, 1994. Contribution to petrological and stratigraphical understanding of the Cordillera de Guanacaste lava flows, Costa Rica. Rev Geol Amer Central, 17: 19-43.

Deering C D, Vogel T A, Patino L C, Alvarado G E, 2007. Origin of distinct silicic magma types from the Guachipelin caldera, NW Costa Rica: evidence for magma mixing and protracted subvolcanic residence. J Volc Geotherm Res, 165: 103-126.

IAVCEI, 1973-80. Post-Miocene Volcanoes of the World. IAVCEI Data Sheets, Rome: Internatl Assoc Volc Chemistry Earth's Interior..

Kempter K A, Benner S G, Williams S N, 1996. Rincon de la Vieja volcano, Guanacaste province, Costa Rica: geology of the southwestern flank and hazards implications. J Volc Geotherm Res, 71: 109-127.

Kempter K A, Rowe G L, 2000. Leakage of active crater lake brine through the north flank at Rincon de la Vieja Volcano, Northwest Costa Rica, and implications for crater collapse. J Volc Geotherm Res, 97: 143-159.

Mainieri P A, 1976. Proyecto geotermico de Guanacaste: informe de previabilidad tecnica. Inst Costarricense de Electricidad (ICE), 97 p.

Mooser F, Meyer-Abich H, McBirney A R, 1958. Central America. Catalog of Active Volcanoes of the World and Solfatara Fields, Rome: IAVCEI, 6: 1-146.

Sapper K, 1925. The Volcanoes of Central America. Halle: Verlag Max Niemeyer, 144 p.

Siebert L, Alvarado G E, Vallance J W, van Wyk de Vries B, 2006. Large-volume volcanic edifice failures in Central America and associated hazards. In: Rose W I, Bluth G J S, Carr M J, Ewert J W, Patino L C, Vallance J W (eds), Volcanic hazards in Central America, {Geol Soc Amer Spec Pap}, 412: 1-26.

Smithsonian Institution-SEAN, 1975-89. [Monthly event reports]. Bull Scientific Event Alert Network (SEAN), v 1-14.

Soto G, Alvarado G E, Goold S, 2003. Erupciones <3800 a.P. del volcan Rincon de la Vieja, Costa Rica. Rev Geol Amer Central, 29: 67-86.

Stine C M, Banks N G, 1991. Costa Rica volcano profile. U S Geol Surv Open-File Rpt, 67 p.

Thorpe R S, Brown G, Rymer H, Barritt S, Randal M, 1985. Recent volcano monitoring in Costa Rica. Earthq Inf Bull, 17: 44-49.

Vogel T A, Patino L C, Alvarado G E, Gans P B, 2004. Silicic ignimbrites within the Costa Rican volcanic front: evidence for the formation of continental crust. Earth Planet Sci Lett, 226: 149-159.

Volcano Types

Complex
Caldera(s)

Tectonic Setting

Subduction zone
Continental crust (> 25 km)

Rock Types

Major
Andesite / Basaltic Andesite
Rhyolite
Dacite

Population

Within 5 km
Within 10 km
Within 30 km
Within 100 km
271
1,428
78,668
659,105

Affiliated Databases

Large Eruptions of Rincon de la Vieja 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.