San Miguel

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  • Country
  • Volcanic Region
  • Primary Volcano Type
  • Last Known Eruption
  • 13.434°N
  • 88.269°W

  • 2130 m
    6986 ft

  • 343100
  • Latitude
  • Longitude

  • Summit
    Elevation

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    Number

23 July-29 July 2014

SNET reported seismic activity at San Miguel during 23-29 July. On 24 July an ash cloud from a small explosion rose 400 m and drifted SW and deposited small amounts of ash in La Morita, Piedra Azul, and San Rafael East. Ash clouds from small explosions on 27-28 July deposited small amounts of ash to the SW in the La Morita Townships of La Piedrita and La Ceiba.

Source: Servicio Nacional de Estudios Territoriales (SNET)

Index of Weekly Reports


2014: January | April | May | June | July
2013: December
2011: March
2010: August
2009: July
2006: October
2005: October
2004: February
2002: October

Weekly Reports


23 July-29 July 2014

SNET reported seismic activity at San Miguel during 23-29 July. On 24 July an ash cloud from a small explosion rose 400 m and drifted SW and deposited small amounts of ash in La Morita, Piedra Azul, and San Rafael East. Ash clouds from small explosions on 27-28 July deposited small amounts of ash to the SW in the La Morita Townships of La Piedrita and La Ceiba.

Source: Servicio Nacional de Estudios Territoriales (SNET)


16 July-22 July 2014

SNET reported elevated seismic activity at San Miguel on 17, 19, 20, and 22 July. RSAM had increased significantly. SO2 flux measurements indicated variability in air quality, which at times reached unhealthy levels.

Source: Servicio Nacional de Estudios Territoriales (SNET)


9 July-15 July 2014

According to the Ministry of Environment and Natural Resources (MARN), elevated activity was detected on 10 July from San Miguel. RSAM had increased significantly and was also high on 14 July, but decreased the next day. On 15 July MARN reported that seismicity was continuing from the N flank. SO2 flux measurements indicated a significant decrease of gas.

Sources: Servicio Nacional de Estudios Territoriales (SNET); Servicio Nacional de Estudios Territoriales (SNET)


25 June-1 July 2014

MARN issued a special report on 27 June and related the unstable system at San Miguel as RSAM values decreased then climbed to fluctuate between 118 and 335. Concentrations of sulfur dioxide (SO2) values measured over the past 24 hours have fluctuated between good and unhealthy.

Source: Servicio Nacional de Estudios Territoriales (SNET)


11 June-17 June 2014

According to SNET, the Ministerio de Medio Ambiente y Recursos Naturales (MARN) reported that seismicity at San Miguel increased significantly during 11-12 June, and remained very high through 17 June. Webcam images on 17 June showed a small steam plume rising from the summit crater.

Source: Servicio Nacional de Estudios Territoriales (SNET)


4 June-10 June 2014

According to SNET in a report from 1 June, the Ministerio de Medio Ambiente y Recursos Naturales (MARN) reported that seismicity at San Miguel remained high. Locals observed more intense gas plumes rising from the crater with occasional and minor amounts of ash, especially after rain. Rumbling was also reported.

Source: Servicio Nacional de Estudios Territoriales (SNET)


28 May-3 June 2014

According to SNET in a report from 1 June, the Ministerio de Medio Ambiente y Recursos Naturales (MARN) reported that seismicity at San Miguel remained high. Locals observed more intense gas plumes rising from the crater with occasional minor amounts of ash, especially after rainfall. Rumbling was also reported.

Source: Servicio Nacional de Estudios Territoriales (SNET)


21 May-27 May 2014

According to SNET, the Ministerio de Medio Ambiente y Recursos Naturales (MARN) reported that during 22-23 May heavy rains at San Miguel caused lahars that originated from the upper part of the volcano and were heard by residents. Seismicity and gas output both remained high. Gas plumes rose 300 m and drifted W; the plumes were different colors and suggested that fine material was being carried out of the crater.

Source: Servicio Nacional de Estudios Territoriales (SNET)


14 May-20 May 2014

According to SNET, the Ministerio de Medio Ambiente y Recursos Naturales (MARN) reported on 19 May that activity at San Miguel had increased significantly in the previous few days. The activity was characterized by an increase in the frequency and magnitude of gas emissions, rumbling in the crater, and small explosions followed by juvenile ashfall. On 18 May between 2230 and 2300 less than 1 mm of ash fell to the WNW in San Jorge. On 19 May the webcam recorded periodic pulses of gray gas plumes that rose 300 m and drifted W. On 20 May seismicity remained high and gray emissions rose 300 m.

Source: Servicio Nacional de Estudios Territoriales (SNET)


7 May-13 May 2014

According to SNET, the Ministerio de Medio Ambiente y Recursos Naturales (MARN) reported that on 10 May San Miguel emitted small amounts of ash. Ashfall, less than 1 mm thick, was observed in areas between the Parque de las Placitas and Placitas.

Source: Servicio Nacional de Estudios Territoriales (SNET)


9 April-15 April 2014

According to SNET, the Ministerio de Medio Ambiente y Recursos Naturales (MARN) reported that on 12 April moderate to strong gas plumes from San Miguel rose from the crater and drifted SW. The most robust plume occurred at 1607 and rose 400 m. Images recorded by a webcam showed that the plumes had dark tones, suggesting small amounts of ash.

Source: Servicio Nacional de Estudios Territoriales (SNET)


15 January-21 January 2014

SNET reported that during 15-20 January RSAM values at San Miguel fluctuated between 14 and 97, except for a period starting at 1500 on 19 January where the values were 102-215. Gas emissions were characterized by light gray plumes that rose 100-250 m above the crater and drifted S and SW.

Source: Servicio Nacional de Estudios Territoriales (SNET)


8 January-14 January 2014

SNET reported that during 8-10 January activity at San Miguel was low. The number of seismic events fluctuated but remained at low levels, sometimes lower than values recorded before the eruption on 29 December 2013. Gas emissions were also low and characterized by light gray plumes that rose 100-150 m above the crater and drifted S. RSAM values and sulfur dioxide emissions increased for a period of time during 11-12 January, but decreased again to low levels.

Source: Servicio Nacional de Estudios Territoriales (SNET)


1 January-7 January 2014

SNET reported that sulfur dioxide gas flux in tonnes per day from San Miguel was high: 2,200 on 31 December 2013, 1,740 on 1 January 2014, and 700 on 2 January. The report noted that the measurement on 2 January was likely low due to changes in wind patterns that day. During 1-2 January RSAM values ranged from 17 to 28 units. On 5 January gas plumes rose as high as 150 m above the crater. The next day light-gray gas plumes rose 200 m and drifted SW. RSAM values during 5-6 January were between 15 and 33 units.

Source: Servicio Nacional de Estudios Territoriales (SNET)


25 December-31 December 2013

According to news articles, an explosive eruption at San Miguel that began at 1030 on 29 December prompted an evacuation of 1,400-2,600 people. A dense ash plume rose from the crater. Based on wind data, the Washington VAAC reported that the ash plume rose to an altitude of 9.7 km (32,000 ft) a.s.l. and drifted ENE at higher altitudes and W at lower altitudes.

SNET reported that sulfur dioxide flux was 637 tonnes per day on 29 December and 1,244 tonnes per day on 30 December. During 30-31 December seismicity decreased significantly. Through the morning of 31 December emissions had consisted of gas and slight amounts of ash that drifted WSW.

Sources: Servicio Nacional de Estudios Territoriales (SNET); Washington Volcanic Ash Advisory Center (VAAC); United Press International (UPI); elsalvador.com


23 March-29 March 2011

Servicio Nacional de Estudios Territoriales (SNET) reported that during a survey of the San Miguel crater on 9 and 16 March observers noted pulses of gas rising 200 m from the crater. On 12 March the number and amplitude of earthquakes increased. RSAM values rose the next day to 121 units per day on average, up from normal values around 50 units per day. RSAM values continued to fluctuate during the next few days and reached as high as 319 units on 19 March, 414 units on 20 March, and 234 on 21 March. On 18 and 20 March, local residents felt vibrations and heard minor rumbling. Observations on 25 March indicated that gas plumes rose 100 m from the crater. On 28 March SNET noted that seismicity had gradually decreased during the previous few days, and was as low as 80 RSAM units on 27 March. Access to areas within a 2-km-radius remained restricted.

Source: Servicio Nacional de Estudios Territoriales (SNET)


11 August-17 August 2010

On 13 August, Servicio Nacional de Estudios Territoriales (SNET) reported that seismicity remained above background levels after an increase was detected on 1 August. Average background RSAM values ranged from 15 to 50 units per day. During 12-13 August, RSAM values ranged between 433 and 465. Over the next few days, seismicity decreased significantly; from 14 August to 16 August, RSAM values decreased from 188 to 132. Access to areas within a 2-km-radius remained restricted.

Source: Servicio Nacional de Estudios Territoriales (SNET)


15 July-21 July 2009

On 20 July, Servicio Nacional de Estudios Territoriales (SNET) reported that the amplitude of seismic events from San Miguel had decreased to normal or background levels. Access to areas within a 2-km-radius continued to be restricted.

Source: Servicio Nacional de Estudios Territoriales (SNET)


8 July-14 July 2009

Servicio Nacional de Estudios Territoriales (SNET) reported that the amplitude of seismic events from San Miguel had decreased during 9-13 July, but RSAM values remained above the background average. Access to areas within a 2-km-radius was restricted.

Source: Servicio Nacional de Estudios Territoriales (SNET)


1 July-7 July 2009

Servicio Nacional de Estudios Territoriales (SNET) reported that seismic amplitude from San Miguel increased for a period of time between 0500 and 1400 on 6 July. Seismicity remained elevated above background levels on 7 July.

Source: Servicio Nacional de Estudios Territoriales (SNET)


11 October-17 October 2006

Servicio Nacional de Estudios Territoriales (SNET) reported on 10 October that an Alert Level for San Miguel was established as Green within 4 km from the center of the crater due to a slight increase in seismic activity. On 15 October, the Alert Level was increased to Yellow due to further increases in seismic activity, but then decreased to Green again the next day.

Source: Servicio Nacional de Estudios Territoriales (SNET)


12 October-18 October 2005

SNET reported that activity had not changed at San Miguel after small clusters of earthquakes occurred at the volcano during 27 September to about 14 October. During a visit to the volcano on 13 October small rockfalls were seen, but there were no significant changes in the crater and sulfur-dioxide emissions were very weak.

Source: Servicio Nacional de Estudios Territoriales (SNET)


11 February-17 February 2004

According to a news article, a tectonic earthquake near San Miguel on the evening of 8 February caused landslides within the crater and on the volcano's flanks. One of the landslides threatened retention walls in the community of Carretos near the volcano. Citizens feared that heavy rains in the future could mix with the landslide material and overload the retention walls, causing them to fail.

Source: La Prensa Grafica


30 October-5 November 2002

A news report stating that a rockslide released dangerous fumes at San Miguel on 17 October was found to be false.

Source: Associated Press


23 October-29 October 2002

A news report stating that a rockslide released dangerous fumes at San Miguel on 17 October was found to be false.

Source: Associated Press


Index of Monthly Reports

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

04/1970 (CSLP 32-70) Eruption during 30 March-4 April causes ashfall 10 km away

12/1976 (SEAN 01:15) Explosive eruption began on 2 December; ashfall damages crops

03/1977 (BVE 17) New spatter cone in the central crater

12/1980 (SEAN 05:12) Small vapor plume

01/1986 (SEAN 11:01) Ash emission and seismicity

03/1995 (BGVN 20:03) Increased seismicity and minor ashfall near the crater

02/2002 (BGVN 27:02) Minor gas-and-ash emission in January 2002; summary of earlier activity

10/2006 (BGVN 31:10) Restlessness persists during 2005-6; heavy tropical rains trigger lahars

09/2007 (BGVN 32:09) Background seismicity since October 2006; crater visit in July 2007


Contents of Monthly Reports

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

All times are local (= UTC - 6 hours)

04/1970 (CSLP 32-70) Eruption during 30 March-4 April causes ashfall 10 km away

Card 0902 (03 April 1970) Renewed activity on 30 March

Reports arriving from the city of San Miguel state that Chaparraspique [Chaparrastique] volcano has again become active, at times intensively. It was reported that the first signs that the volcano had become active were noticed at 1300 GMT 30 March and that it continues to be covered by a layer of smoke and mist, which indicates that it may become active again at any moment, forcing the authorities to evacuate the area populated by hundreds of families.

Card 0904 (07 April 1970) Ashfall extends 10 km from the summit; crater visit

"Ash erupted from the crater of San Miguel volcano, El Salvador, on 30 March 1970, at 0230, 0700, and 0800. The first ash eruption, accompanied by a loud noise heard four kilometers away, reached a height of 400 m above the crater floor, according to Sr. Santiago Ventura Arevalo, Secretary of the Finca la Placita, San Miguel, and a report in La Prensa (San Salvador) of 31 March 1970. Ash fell in a fan-shaped area extending at least 10 km NE of the summit. From measurements of ash deposits three and four days after the eruption, the minimum volume of ash is estimated to be 75,000 m3. At the time of the ascent into the crater on 4 April 1970, there was ash in the crater floor to a depth of 15 mm. Infrequent ash eruptions up to 100 m high were observed on 3 and 4 April from the deep chimney in the summit crater. A land-based infrared radiation thermometry survey on 4 April detected no anomalous heat patterns on the NW side of the cone."

Information Contacts:
Card 0902 (03 April 1970) San Salvador Domestic Service, El Salvador.
Card 0904 (07 April 1970) Richard E. Stoiber, Dartmouth College, USA; Ian Lange, Fresno State College; Richard Birnie, USA Cold Reg. Research and Engineering Laboratory.

12/1976 (SEAN 01:15) Explosive eruption began on 2 December; ashfall damages crops

An explosive eruption of San Miguel was reported to have begun during the morning of 2 December. "Smoke", loud noises, and a sulfur smell were reported from the nearby town of San Miguel. By 9 December, the eruption cloud was visible from a considerable distance and ashfalls had caused some crop damage. A few persons were evacuated. Although "fire" was reported by the press, only a white cloud was seen by Richard Stoiber during a 9 December overflight. The last activity at San Miguel was the eruption of more than 75,000 m3 of ash beginning 30 March 1970.

Further Reference. Martinez, M.A., 1977, The eruption of 2 December, 1976 of San Miguel Volcano, Republic of El Salvador, Central America: Centro de Investigaciones Geotécnicas, San Salvador, 4 p.

Information Contacts: AFP; Sercano Radio Network; R. Stoiber, Dartmouth College.

03/77 (BVE 17) New spatter cone in the central crater

The following is based on a report in BVE 17. After 6 years of dormancy since the last activity in 1970, San Miguel started erupting at about 0030 on 2 December 1976. The eruption was characterized by lava fountains. On 12 December the eruption stopped, and fumarole activity was seen around a new spatter cone in the bottom of the central crater. Fifty-six days later, the activity started again during the night of 28 February and lasting until 1 March 1977.

Information Contacts: M.A. Martinez, Centro de Investigaciones Geotécnicas, San Salvador, El Salvador.

12/1980 (SEAN 05:12) Small vapor plume

During a flight over El Salvador by Dartmouth geologists, a small, continuous vapor plume rose from the summit crater.

Information Contacts: R. Stoiber, S. Williams, R. Naslund, L. Malinconico, and M. Conrad, Dartmouth College.

01/1986 (SEAN 11:01) Ash emission and seismicity

Weak steam and ash emission accompanied by frequent small earthquakes began in November and were continuing in early February. The eruption deposited a thin layer of ash near the summit. Geologists installed a telemetering seismometer about 1 km from the summit, recording about 200 discrete microseismic events/day from November through much of January. By the end of January, seismic activity had declined somewhat, to 100-120 events/day.

Information Contacts: José González and Salvador Jesus, Dept de Sismología, Centro de Investigaciones Geotécnicas, San Salvador, El Salvador; David Harlow, USGS.

03/1995 (BGVN 20:03) Increased seismicity and minor ashfall near the crater

New fumaroles were found near the central vent in early January, followed by an increase in seismic activity from an average of 20-30 events/day. On 8 February there were 52 recorded earthquakes. Seismicity increased to 73 events on 19 February, 100 on the 20th, and peaked at 267 on the 21st. This activity then declined on 22 February to an average of 76 events/day, a rate which continued through at least 24 March. Minor ashfall was reported on 23 March within ~100 m of the crater.

The Centro de Investigaciones Geotécnicas (CIG) concluded that this activity was no cause for alarm, but they would increase their monitoring efforts. The population at risk from an eruption with significant ashfall is a mix of urban and rural residents. The city of San Miguel (at the foot of the W flank) has a population of ~150,000, and the rural zone that would likely be affected has a population of ~100,000.

Information Contact: Jorge Alberto Rodríguez Deras, Director, Centro de Investigaciones Geotécnicas, San Salvador, El Salvador.

02/2002 (BGVN 27:02) Minor gas-and-ash emission in January 2002; summary of earlier activity

On 16 January 2002 a gas-and-steam plume containing a little ash rose with a mushroom-like profile a few hundred meters above the summit crater of San Miguel. During a visit to the summit on 28-29 January, Demetrio Escobar and a group from Michigan Technological University observed a thin layer of ash inside the summit crater produced by the 16 January event. COSPEC measurements of 100 metric tons/day were recorded at a time that the plume from San Miguel rose about 100 m above the crater rim. Long-period earthquakes, volcanic tremor, and explosion events were recorded at San Miguel in late January and February. This style of increased seismicity and gas emission is within the range of normal activity at San Miguel, and the Servicio Geologico de El Salvador concluded that this activity was no cause for alarm, but planned the installation of more telemetry seismic stations. The population at risk from an eruption with significant ashfall is a mix of urban and rural residents. The city of San Miguel (at the foot of the W flank) has a population of ~150,000, and the rural zone that would likely be affected has a population of ~100,000.

The events at San Miguel received extensive coverage in the local press, which had previously reported ash eruptions on 25 December 2001. However, during field studies around the volcano during 4-6 January by Escobar and Craig Chesner, extensive interviews of local residents revealed that the report of ashfall was incorrect. Vigorous steam plumes from the volcano had been confused with fly ash from the burning of sugar cane fields.

Summary of previous activity. Intermittent periods of vigorous steam-and-gas emission from San Miguel have been commonly reported in recent years. On at least two occasions, in early 1995 and at the end of December 1997, minor gas-and-ash emissions had occurred. Although discussed previously in BGVN 20:03, Escobar provided additional information on the 1995 event. Elevated seismicity and gas emission occurred at San Miguel from 26 December 1994 to 11 January 1995.

On 12 January 1995 Escobar visited the volcano and heard jet-like sounds at the crater, along with probable small explosions. Gas emission formed a plume about 100 m high that was blown to the SW. Escobar found 3-4 mm of ash in the summit crater. He also observed fine ashfall deposits on the SW flank and measured up to 2-3 mm of gray ash on the NW flank at a distance of 3 km from the crater. Residents reported that the ashfall caused damage to coffee plantations.

Elevated seismicity continued, and similar conditions were observed during a visit to the crater in February 1995. On 20 March the telemetered seismic station worked only 11 hours, but registered 48 events, including 4 volcanic tremor events and 39 LP events. Three events were felt by residents living near the volcano.

At the time of a 23-24 April 1995 visit, residents reported they had not felt any seismic events, but that ashfall had occurred on 19 April following a rainstorm. Seismicity returned to normal in May of that year.

On 17 June 1996 seismic stations registered a seismic swarm at San Miguel volcano during 1128 to 1333, consisting of 24 volcano-tectonic events with a maximum magnitude of 2.5. No felt events were reported.

Residents living near the volcano reported minor ashfall on 31 December 1997, although no geologists were present to document the ashfall distribution. On 13 January 2000, volcanic tremor was recorded for 15 minutes. On 25 January, 17 minutes of tremor occurred, along with explosion events. During May tremor was recorded for a total of 2.5 hours, and intervals of long-period earthquakes, volcanic tremor and explosion events occurred later in the year.

On 26 August 2000 a lahar from San Miguel damaged houses and a highway N of the volcano, and a similar event on 6 September 2001 affected a highway. Previously lahars had destroyed or damaged houses and highways N of the volcano on 7 May 1985 and 28 September 1992.

Information Contacts: Carlos Pullinger and Demetrio Escobar, Seccion Vulcanologia, Servicio Geológico de El Salvador, c/o Servicio Nacional de Estudios Territoriales, Alameda Roosevelt y 55 Avenida Norte, Edificio Torre El Salvador, Quinta Planta, San Salvador, El Salvador (Email: pulga@salnet.net; cdescoba@mtu.edu); Gustavo Chigna, Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hidrologia (INSIVUMEH), Ministero de Communicaciones, Transporto, Obras Públicas y Vivienda, 7a. Av. 14-57, zona 13, Guatemala City 01013, Guatemala (http://www.insivumeh.pagina.de), Bill Rose, Liset Rodríguez, Gustavo Chigna, Otoniel Matías, Janelle Byman, Elly Bunzendahll, Ivonne Branan, and Matt Watson, Michigan Technological University, Houghton, MI 49931 USA (Email: raman@mtu.edu).

10/2006 (BGVN 31:10) Restlessness persists during 2005-6; heavy tropical rains trigger lahars

According to El Salvador's Servicio Nacional de Estudios Territoriales (SNET) activity levels at San Miguel have generally remained similar to those during January 2002 when a minor plume rose above the summit crater (BGVN 27:02). The volcano's vigor continued into at least October 2006 at a level slightly at or above the base line of normal activity.

Recent publications have discussed the volcano and its lahar-hazard potential (Escobar, 2003; Chesner and others, 2003; Major and others, 2001). Figures 1 and 2 are taken from the latter publication.

Figure 1. Index map indicating El Salvador's volcanic front and the location of volcan San Miguel. Major cities are also shown (circles). From Major and others (2001).
Figure 2. The lahar hazard map of San Miguel depicts likely lahar paths, which are shown as colored or shaded areas. The contour interval is 20 m; the urban center ~ 11 km NE of the summit is San Miguel. From Major and others (2001); their plate 1, cropped, highly reduced, and excluding the key.

In January 2005 observers saw new fumaroles as well as small landslides on the N and SW wall of the crater. The accumulation of mass-wasted material in the crater led to a rise in the elevation of the crater floor.

During February 2005, weak fumaroles and small rock landslides persisted in the central crater. Digital sensors installed there recorded fumarolic temperatures in real time. On the outer portions of the cone the terrain is steeply sloping and contains prominent gullies (figure 3).

Figure 3. A photo of San Miguel taken from the N on 22 February 2005 showing the steep sides of the upper slopes and the incised drainages there. Although much of the area on the volcano is rural, hazards could easily affect 40,000 residents living nearby. Courtesy of Servicio Nacional de Estudios Territoriales (SNET).

The SNET reports for March and April 2005 noted that the crater was structurally weak due to the fumarolic activity, ongoing rock alteration, occasional landslides, and fractures on the western plateau. Microseismicity had increased; but it did not exceed typical base-line levels. Workers at the Santa Isabel farm (finca) noted N-flank lahars after heavy rains during March. The N flank contains abundant fine-grained volcanic deposits of the sort easily swept away during times of heavy rain.

Intense rains during May 2005 were associated with tropical storm Adrian (over an unstated interval the meteorological station near the volcano, San Miguel UES, recorded 428 mm of rainfall). As a result of the deluge, fumarolic activity from the crater increased. The crater walls remained intact, but eroded material previously deposited in the central crater that was poorly consolidated had to some degree stabilized. Substantial further compaction, settling, or collapse in the central crater seemed to have ceased by July 2005. During August 2005 the crisis at volcan Santa Ana forestalled visits to San Miguel.

A spike in seismic activity occurred during August 2005, with 7,048 long-period earthquakes, compared to July 2005, with 2,239 long-period earthquakes. SNET reports noted that based on monitoring, San Miguel generally remained within its base-line of normal behavior during the reporting interval. Figure 4 shows a histogram of long-period and volcano-tectonic events from the SNET reports for the interval September 2005-June 2006.

Figure 4. A plot of seismicity at San Miguel during September 2005-June 2006. Courtesy of SNET.

On 14 September 2005 a visiting group (OIKOS- Soliradaridad Internacional) made a trek to the summit and videotaped the scene there. SNET said the video disclosed a lack of significant changes in the crater; however, they saw debris-flow deposits in summit drainages on the volcano's outboard flanks. The visitors described both sounds of degassing and moderately intense odors of H2S. During the course of September the seismic system recorded several minutes of tremor.

The October 2005 SNET report noted that workers at the plantation Santa Isabel noted N-slope lahars associated with rainfall. The lahars were also described as small debris flows; they descended from the high-elevation headwater areas, which are steep sided and narrow. The November report commented about the quantity of debris-flow material accumulating at the base of some N-flank channels. The same report also mentioned that moderate degassing was seen in the crater leaving areas of abundant sulfur, which appeared as yellow zones in one or more fumarolic areas.

The November 2005 report of SNET also discussed substantial landslides inside the crater that were followed by widening of the funnel-shaped area of collapse in the central crater. The landslides had left three distinct perched remnants of the crater floor (small terraces) at various elevations on the crater walls. The crater's western plain (one such terrace of the sort mentioned above) was stable but showed areas of subsidence (figure 5).

Figure 5. (top) A photo of San Miguel taken on 16 November 2005 showing the 'western plain' of San Miguel's crater (a terrace representing a remnant of a former crater floor). A considerable portion of the remaining terrace is in the process of subsidence (slumping). (bottom) A photo of the same area taken on 15 February 2006 (looking S). A zone of local subsidence, a pit along the head scarp, appears in the foreground but the subsidence also includes the region to the left of the large arcuate area extending well beyond the pit and still conspicuous in the upper left edge of the photograph. Courtesy of SNET.

Lahar monitoring during December 2005 disclosed erosion of easily mobilized cinders and scoria material on the N to NW flanks during the previous wet season. December seismicity was elevated, but cracks in the crater changed little compared to previous measurements. A field team visited the summit on 11 January 2006 and again in February and found few substantive changes in the crater. On the ascent route during January, the team saw a small recent "fall of material" reaching 40 cm thick. Some fumaroles discharged yellowish gases. During February the team conducted measurements of cracks on the western plain but found few changes, suggesting the headscarp had moved little if at all. February and March tremor episodes were centered at ~ 5 Hz and lasted 1-3 minutes.

The March 2006 SNET report noted small rockslides on the crater's N and S sides and, with the beginning of the rainy season in March 2006, there was a potential for the development of lahars. During the March visit the team found abundant granular material in the gullies on the NW flank, judged to be the result of debris flows. Monitored cracks remained stable.

With the arrival of the wet season in April, lahars and enhanced fumarolic output became apparent. One debris flow intersected a highway. On 23-24 April, 105 mm of rain was recorded at plantation (finca) Santa Isabel. Figure 6 shows the results of one lahar which left a trail of debris during the rainy interval. Earlier in the month on the 16th, a tremor or multi-phase episode lasted over an hour.

Figure 6. A San Miguel photo showing a part of the freshly scoured upslope channel in the Gato erosional gully. The material deposited in the channel consisted of reworked volcanic rocks and must have descended as a small lahar or debris flow. Several such flows occurred during heavy late-April rains at the start of the rainy season, a few days before this picture was taken. Courtesy of SNET (from their April 2006 report).

In April 2006, an increase in fumarole degassing within the crater and small landslides contributed to the instability of the deposits on the NW flanks of the volcano. Steam emanated from the fumaroles occasionally forming a weak column that reached the edge of the crater. There was a slight increase in seismicity throughout the month. Seismic activity increased in March and April 2006 (figure 4). Rocks in the crater show intense hydrothermal alteration with a yellowish reddish color. Small rock landslides were observed in the N and S zone of the crater.

During June 2006, the temperature of the fumaroles, opening of cracks and the gas discharge by the crater of the volcano, remained stable. There was an increase of small landslides within the crater. The analysis of the seismicity indicates that the volcano is slightly above its base line of normal behavior. New landslides and cracked rock were observed in the walls of the crater (figure 7). Rains have transferred volcanic material down the NW flank. Seismicity gradually increased in both frequency and magnitude beginning on 16 June. 47 VT earthquakes and 7,505 LP earthquakes were recorded, an amount that surpasses those registered in May; but smaller than those registered in March and April (figure 4).

Figure 7. San Miguel's S crater wall exposes zones of altered and fractured rocks. A planar zone of structural weakness appears towards the right. Photo taken on 22 June 2006. Courtesy of SNET.

During July 2006, stability continued with respect to fumarole temperatures, crack openings, and gas emissions around the crater. However, the seismicity increased by ~ 70%. Small and sporadic landslides took place inside the crater off the SE to SW walls. Intense hydrothermal alteration in the NW wall was also observed. SNET did not report any lahars during July 2006; however intense rains have continued to remove volcanic material from the NW flanks. The fumarolic field gave off weak emissions.

In August 2006, the monitored parameters such as fumarole temperature, crack opening, and visual estimates of gas discharge maintained normal levels. The seismicity diminished significantly in relation to July.

During September 2006, San Miguel reached a low level of activity. There were no significant changes in the morphology of the volcano as reported in previous months. At the S wall, there were evidence of small rock slides.

A sudden increase in seismicity occurred on 9 October 2006. Contact was made with other observatories and it was determined there were no landslides or rock falls associated with the event. Seismic increases such as 9 October had previously occurred, particularly on 19 June 2003 and from 2-6 May 2004. The 9 October increases were attributed to gas emission from the crater.

References. Chesner, C. A., Pullinger, C., Escobar, C. D., 2003, Physical and chemical evolution of San Miguel Volcano, El Salvador. GSA Special Paper 375.

Escobar, C.D., 2003, San Miguel Volcano and its Volcanic Hazards; MS thesis, Michigan Technological University, December 2003. 163 p.

Major, J.J.; Schilling, S.P., Pullinger, C.R., Escobar, C.D., Chesner, C.A, and Howell, M.M., 2001, Lahar-Hazard Zonation for San Miguel Volcano, El Salvador: U.S. Geological Survey Open-File Report 01-395. (Available on-line.)

Information Contacts: Carlos Pullinger, Seccion Vulcanologia, Servicio Geológico de El Salvador, c/o Servicio Nacional de Estudios Territoriales, Alameda Roosevelt y 55 Avenida Norte, Edificio Torre El Salvador, Quinta Planta, San Salvador, El Salvador (URL: http://www.snet.gob.sv/Geologia/Vulcanologia/).

09/2007 (BGVN 32:09) Background seismicity since October 2006; crater visit in July 2007

A sudden increase in seismicity occurred on 9 October 2006 but no landslides or rock falls were associated with the event and it was attributed to gas emissions in the crater (BGVN 31:10). This report carries on from 9 October 2006.

During the morning of 10 October 2006, seismic activity declined to a continuous vibration with an amplitude that oscillated between 50 and 75 RSAM (real-time seismic amplitude measurement) units. This condition continued until 0600 on 11 October, when the seismicity increased to 125 continuous RSAM units.

The responsible authorities issued an alert that encompassed an area within 4 km from the center of the crater. Because of the elevated energy level of seismicity relative to the previous activity, the National Service of Territorial Studies elected to monitor the volcano and report developments to the National System of Civil Defense.

As of 15 October 2006, the level of activity at San Miguel was considered to be moderate, implying the possibility of an eruption sometime in the next several months. The civil defense authorities established a Yellow alert level (phase 3) for the area within 4 km of the crater center but later reduced it to Green. Around 15 October the RSAM continued to vary from 8 units to 45 units. During the preceding 24 hours, 55 earthquakes were registered; however, none were noticed by the local population. Sulfur dioxide (SO2) fluxes reached 150-250 metric tons per day, which was considered a low level. On 16 October, tremor fluctuated between 45 and 50 units, and 25 earthquakes were recorded but not felt by residents.

The period from the October 2006 activity through July 2007 was essentially devoid of any abnormal variations in seismicity, volcanism, or elevated gas emissions.

On 4 July 2007, volcanologists from Servicio Nacional de Estudios Territoriales (SNET) and Michigan Technological University climbed San Miguel to make observations and take fumarole temperatures. The volcano remained at a low level of activity. The crater morphology and the intensity and location of fumaroles within the crater remained similar to that observed in recent visits (e.g., October 2006 BGVN 31:10). The main fumarolic area was near the bottom of the crater on the S wall (figure 8). Other sparse fumaroles were present, with most clustered near the crater bottom and on the crater's W wall.

Figure 8. View of the crater at San Miguel, looking S on 4 July 2007. The whitish area in the bottom right of the photo reflects steaming from the main fumarole field. Courtesy of Servicio Nacional de Estudios Territoriales (SNET) and Michigan Technological University.

Fumarole measurements: Temperatures were measured at two fumarolic areas on the upper W crater wall (figure 9). These are visited by SNET on a regular basis and comprise the only fumaroles safely accessible from the rim. Temperatures at fumaroles 1 and 2 were 67°C and 57°C, respectively. The gas lacked any sulfurous smell, suggesting water vapor only. These fumarole temperatures are similar to those measured in recent visits.

Figure 9. View of the W side of San Miguel's crater, taken from the N rim. Fumaroles 1 (F1) and 2 (F2) are in the right central portion of the image. Courtesy of Servicio Nacional de Estudios Territoriales (SNET) and Michigan Tech University.

References. Chesner, C.A., Pullinger, C., Escobar, C.D., 2003, Physical and chemical evolution of San Miguel Volcano, El Salvador. GSA Special Paper 375.

Escobar, C.D., 2003, San Miguel Volcano and its Volcanic Hazards: MS thesis, Michigan Technological University, December 2003, 163 p.

Major, J.J., Schilling, S.P., Pullinger, C.R., Escobar, C.D., Chesner, C.A, and Howell, M.M., 2001, Lahar-Hazard Zonation for San Miguel Volcano, El Salvador: U.S. Geological Survey Open-File Report 01-395 (Available on-line).

Information Contacts: Eduardo Gutierrez, Demetrio Escobar, and Francisco Montalvo, Servicio Nacional de Estudios Territoriales (SNET), Km. 5 ½ carretera a Santa Tecla y Calle las Mercedes, contiguo a Parque de Pelota, Edificio SNET, Apartado Postal #27, Centro de Gobierno, El Salvador (URL: http://www.snet.gob.sv/, Email: egutierrez@snet.gob.sv, descobar@snet.gob.sv, fmontalvo@snet.gob.sv); Matthew Patrick and Anna Colvin, Dept. of Geological and Mining Engineering and Sciences, Michigan Tech University, 1400 Townsend Drive, Houghton, MI 49931, USA (Email: mpatrick@mtu.edu; ascolvin@mtu.edu).

The symmetrical cone of San Miguel volcano, one of the most active in El Salvador, rises from near sea level to form one of the country's most prominent landmarks. The unvegetated summit of the 2130-m-high volcano rises above slopes draped with coffee plantations. A broad, deep crater complex that has been frequently modified by historical eruptions (recorded since the early 16th century) caps the truncated summit of the towering volcano, which is also known locally as Chaparrastique. Radial fissures on the flanks of the basaltic-andesitic volcano have fed a series of historical lava flows, including several erupted during the 17th-19th centuries that reached beyond the base of the volcano on the north, NE, and SE sides. The SE-flank lava flows are the largest and form broad, sparsely vegetated lava fields crossed by highways and a railroad skirting the base of the volcano. The location of flank vents has migrated higher on the edifice during historical time, and the most recent activity has consisted of minor ash eruptions from the summit crater.

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

Start Date Stop Date Eruption Certainty VEI Evidence Activity Area or Unit
2013 Dec 29 2014 Jun 1 (continuing) Confirmed 2 Historical Observations
2002 Jan 16 2002 Jan 16 Confirmed 1 Historical Observations
1997 Dec 31 Unknown Confirmed 1 Historical Observations
1995 Jan 12 1995 Apr 19 Confirmed 1 Historical Observations
1985 Nov 1986 Feb (in or after) Confirmed 1 Historical Observations
1976 Dec 2 1977 Mar 1 Confirmed 1 Historical Observations
1970 Mar 30 1970 Apr 5 Confirmed 1 Historical Observations
1967 Jan 5 Unknown Confirmed 2 Historical Observations
1966 Jul Unknown Confirmed 2 Historical Observations
1966 Feb 22 Unknown Confirmed 2 Historical Observations
1964 Oct 23 1964 Nov Confirmed 2 Historical Observations
1954 Oct 21 1954 Oct 21 Confirmed 2 Historical Observations
1939 May 1939 Jul Confirmed 2 Historical Observations
[ 1936 (?) ] [ Unknown ] Uncertain 2  
1931 Mar 1931 Jun Confirmed 2 Historical Observations
1930 Jan 26 ± 5 days Unknown Confirmed 2 Historical Observations
1929 Aug Unknown Confirmed 2 Historical Observations
1920 Aug 14 1925 Confirmed 2 Historical Observations
1919 Dec 10 1920 Jan Confirmed 2 Historical Observations
1890 1891 Confirmed 2 Historical Observations
1884 Jan 25 1884 Jan 28 ± 1 days Confirmed 2 Historical Observations NE side of main crater
1882 Dec 5 ± 4 days Unknown Confirmed 2 Historical Observations
1867 Dec 14 1868 Feb 16 (in or after) Confirmed 2 Historical Observations WSW flank (1000 m)
1862 Jan Unknown Confirmed 2 Historical Observations
1857 Nov Unknown Confirmed 2 Historical Observations
1855 Dec Unknown Confirmed 2 Historical Observations SSE flank (800 m)
[ 1854 ] [ Unknown ] Uncertain 2  
1844 Jul 25 1848 Confirmed 2 Historical Observations NNW (1120 m) and upper east flanks
1819 Jul 18 Unknown Confirmed 2 Historical Observations SSE flank (400 m; near Los Perolitos)
[ 1811 ] [ Unknown ] Uncertain 2  
[ 1798 (?) ] [ Unknown ] Uncertain 2  
1787 Sep 21 1787 Sep 23 Confirmed 2 Historical Observations Summit, north and SE flanks
1769 Unknown Confirmed 2 Historical Observations East flank ?
1762 Unknown Confirmed 2 Historical Observations NE flank (400 m)
1699 Unknown Confirmed 2 Historical Observations SE flank (400 m)
1510 ± 5 years Unknown Confirmed   Historical Observations

This compilation of synonyms and subsidiary features may not be comprehensive. Features are organized into four major categories: Cones, Craters, Domes, and Thermal Features. Synonyms of features appear indented below the primary name. In some cases additional feature type, elevation, or location details are provided.



Synonyms
Chaparrastique | Perolitos, Los | Bosotlán
The summit of San Miguel volcano contains a deep crater whose morphology has been frequently modified by historical eruptions. In 1586 the volcano already had a truncated summit; before then the volcano was said to have had a sharp peak. In 1866 the crater was 600 m wide and 320 m deep and contained a subcrater on the ENE side. A cinder cone that formed at the NE side of the crater in 1884 had largely disappeared by 1924, and a ring plain on the crater floor was largely gone by 1949.

Copyrighted photo by Dick Stoiber, 1965 (Dartmouth College).
The fresh-looking lava flow at the upper right on the north flank of San Miguel volcano was emplaced during an eruption in 1844. The flow originated on July 25 from a NNW-flank fissure and traveled initially to the NNW before diverting to the NE and reaching to 8 km from the summit. After December the volcano began long-term explosive activity that lasted until 1848, when another lava flow occurred.

Photo by Kristal Dorion, 1994 (U.S. Geological Survey).
Symmetrical San Miguel volcano towers 2000 m above a barren basaltic lava flow erupted from a SE-flank vent in 1819. The conical volcano is not the highest volcano in El Salvador, but is one of the most prominent, since it rises from near sea level on the Pacific coastal plain. San Miguel (also known as Chaparrastique) is one of the most active volcanoes of El Salvador, with more than two dozen eruptions recorded since the beginning of the Spanish era.

Photo by Carlos Pullinger, 1996 (Servicio Nacional de Estudios Territoriales, El Salvador).
Flat-lying Chinameca volcano on the center horizon is truncated by a 2-km-wide caldera. The volcano is seen here from the north, with the summit of San Miguel volcano behind it on the left. A cluster of fumarole fields is located on the northern flank of the volcano surrounding the city of Chinameca.

Photo by Carlos Pullinger, 1996 (Servicio Nacional de Estudios Territoriales, El Salvador).
This large lava bomb in the summit crater of San Miguel was probably erupted in 1976. Lava fountaining took place in the central crater, which was active December 2-12, 1976 and February 28 to March 1, 1977, constructing a new spatter cone. Ashfall in December 1976 caused some crop damage.

Photo by Carlos Pullinger, 1996 (Servicio Nacional de Estudios Territoriales, El Salvador).
The Chinameca volcanic complex on the center horizon is seen here from the west beyond the low-angle slopes of the Pleistocene El Tigre volcano in the foreground. The low, flat-topped peak at the right side of the Chinameca complex is Cerro el Limbo, a cone on the western flank of Chinameca caldera. The high conical peak at the upper right is San Miguel volcano, which is separated by a low saddle from Chinameca.

Photo by Carlos Pullinger, 1994 (Servicio Nacional de Estudios Territoriales, El Salvador).
Conical San Miguel volcano, one of El Salvador's most prominent landmarks, rises across a low saddle SE of Chinameca (Pacayal) volcano. The 2130-m-high San Miguel is seen here from Cerro el Limbo, a cone on the western flank of Chinameca. The southern side of Chinameca's 2-km-wide summit caldera is visible at the left.

Photo by Carlos Pullinger, 1996 (Servicio Nacional de Estudios Territoriales, El Salvador).
San Miguel is one of the most prominent volcanoes in El Salvador. Its southern slopes, seen here, rise more than 2000 m above the farmlands on the Pacific coastal plain. Both summit and flank vents have been active during historical time. The dark-colored lava flow at the right-center was erupted from a SE-flank vent in 1819.

Photo by Rick Wunderman, 1999 (Smithsonian Institution).
An eastward-looking aerial view down the main Salvadoran volcanic front shows San Vicente volcano below the cloud in the foreground and Tecapa, El Tigre, and Usulután volcanoes below the horizon at the upper right. The small cone in the saddle between Usulután and El Tigre is Cerro Oromontique. Behind Tecapa and El Tigre is conical San Miguel volcano, and to its right in the far distance is Conchagua volcano, the easternmost on the Salvadoran mainland.

Photo by Lee Siebert, 1999 (Smithsonian Institution).
The SW side of San Miguel volcano towers more than 2000 m above the Pacific coastal plain; the base of the volcano lies only about 100 m above sea level. The symmetrical volcano is one of the most active in El Salvador and has produced dominantly basaltic and basaltic andesite lava flows and tephra. Frequent eruptions have kept much of the upper part of the edifice unvegetated. Flank vents are concentrated on the SE and NW quadrants of the volcano, but have been active during historical time on all sides.

Photo by Lee Siebert, 1999 (Smithsonian Institution).
The low ridge in the left foreground is the vegetation-covered surface of a SW-flank lava flow erupted in 1867. Lava effusion began on the SW flank on December 14. Explosive activity continued, producing ashfall over the city of Usulután (20 km to the SW) and damaging tobacco plantations. The volcano was reported to be in activity again on February 2 and was particularly active on February 16. Lava fountains produced extensive scoria deposits that mantled the flow, causing it to be more vegetated than older flows.

Photo by Lee Siebert, 1999 (Smithsonian Institution).
The sparsely vegetated basaltic lava flow cutting diagonally across the photo to the upper right was erupted from a NNW-flank vent in 1844. The flow traveled initially to the NNW toward the broad saddle between San Miguel and Chinameca volcanoes and then was deflected to the NE. It traveled in a narrow lobe as far as 8 km from the summit near the path of the present-day road between the town of San Jorge and the city of San Miguel.

Photo by Lee Siebert, 1999 (Smithsonian Institution).
This sparsely vegetated basaltic lava flow was erupted from a fissure vent on the lower SE flank of San Miguel in 1819. The flow covers a broad 2.5-km-wide, 5-km-long area on the low-angle slopes below the volcano and reaches down to an elevation of less than 40 m above sea level. The principal coastal highway of El Salvador traverses the flow below the point of this photo, and the national railway crosses the flow closer to the vent.

Photo by Lee Siebert, 1999 (Smithsonian Institution).
The dark-colored areas at the bottom of the photo are lava flows erupted from a SSE-flank vent of San Miguel in December 1855. The larger dark area above it extending diagonally across the image is a cloud shadow. The 1855 lava flows were erupted from a SSE-trending radial fissure and were the smallest flows erupted at San Miguel in historical time, extending only about a kilometer from the vent.

Photo by Paul Kimberly, 1999 (Smithsonian Institution).
Small cinder cones on the lower SE flank of San Miguel between about 300 and 400 m altitude were constructed along a radial fissure that also was the source of a voluminous basaltic lava flow (foreground) erupted in 1819. The flow traveled about 5 km and covered a broad area below the base of the volcano.

Photo by Paul Kimberly, 1999 (Smithsonian Institution).
The basaltic lava flow in the foreground originated during a major effusive eruption that began from fissure vents on the NNW flank of San Miguel on July 25, 1844. By December lava was confined to the crater. The volcano then entered a several-year-long period of explosive activity. Another lava flow was reported in 1848, the year the eruption ended.

Photo by Paul Kimberly, 1999 (Smithsonian Institution).
This view from the southern crater rim shows the 2030 m high point of San Miguel on the NE rim at the upper right. An ejecta-covered terrace on the eastern side of the crater is truncated by a deep inner crater. The crater morphology has varied dramatically since the beginning of documentation in the 16th century. In 1866 a 600-m-wide, 320-m-deep crater existed in the SE part of the summit crater, while a 100-m-wide, 80-m-deep adventive crater was located in its ENE part.

Photo by Lee Siebert, 1999 (Smithsonian Institution).
The summit crater of San Miguel volcano reflects a complex sequence of events. This view from the northern crater rim shows two lava benches that are truncated by a deep compound central pit crater from which steam plumes rise. The morphology of the summit crater has varied dramatically during historical time. The inner pit crater has gradually expanded to the east and north and increased in depth to nearly 350 m in 1999.

Photo by Lee Siebert, 1999 (Smithsonian Institution).
The dark sparsely vegetated area in the center of the photo marks basaltic lava flows erupted on the SE flank of San Miguel volcano in 1819. The flows, seen here from the summit of San Miguel, originated from fissure vents on the lower SE flank in July 1819 and traveled about 5 km downslope toward Laguna el Jocotal (upper right). The small lava flows at the lower right-center were erupted in December 1855. The principal coastal highway and the national railway of El Salvador cross the 1819 flows.

Photo by Lee Siebert, 1999 (Smithsonian Institution).
The summit of San Miguel volcano was reported to be peaked prior to the 16th century, but now is truncated by a 1-km-wide crater. This aerial view shows the 2130 m high point on the far NE crater rim in the center of the photo and several benches cut by a roughly 250-m-deep central crater. The morphology of the crater has varied greatly during historical time as a result of the creation and subsequent destruction of new craters. A cinder cone that formed in the NE part of the crater in 1884 had disappeared 50 years later.

Photo by Willard Parsons, 1964 (courtesy of Bill Rose, Michigan Technological University).
The northern slopes of the symmetrical cone of San Miguel are seen here from the city of San Miguel north of the volcano. A deep crater that has been frequently modified by historical eruptions (recorded since the early 16th century) caps the truncated summit of the basaltic-to-andesitic volcano. Radial fissures on its flanks have fed a series of fresh lava flows, including a NE-flank flow in 1762 that currently underlies the outskirts of the city of San Miguel, the third largest in El Salvador.

Photo by Bill Rose, 1971 (Michigan Technological University).
This barren lava flow issued from a fissure vent on the SE flank of San Miguel in 1819. The flow traveled about 5 km and covered a broad area below the SE base of the volcano, extending down to 25 m above sea level. Emplacement of the lava flow necessitated the construction of a new road at the base of the volcano.

Photo by Dick Stoiber, 1971 (courtesy of Bill Rose, Michigan Technological University).
The twin summits of San Vicente volcano form one of El Salvador's most prominent natural landmarks. Fresh scarps from landslides produced during the January 2001 earthquake scar the flanks of the volcano. The San Vicente area and towns at the foot of the volcano were particularly hard hit by the tectonic earthquake and suffered extensive damage. The Tecapa volcanic complex and conical San Miguel volcano rise in the distance.

Photo by Paul Kimberly, 2002 (Smithsonian Institution).
An E-W-trending chain of volcanoes extends ca. 30 km across eastern El Salvador. The small light-colored dot at the left is Laguna de Alegria, a crater of the Tecapa volcanic complex. No historical eruptions are known from the eroded Usulután and El Tigre volcanoes. The 2-km-wide Laguna Seca el Pacayal caldera is a prominent feature of Chinameca volcano. San Miguel is one of El Salvador's most active volcanoes; the dark area at the lower right is a lava flow from the 1819 eruption. The city of San Miguel is at the upper right.

NASA Space Shuttle image STS61C-31-47, 1986 (http://eol.jsc.nasa.gov/).
A large eruption took place from San Miguel in 1699, accompanied by strong earthquakes, flames, and rumblings. A major lava flow (right-center) traveled from SE-flank fissures for a straight-line distance of nearly 9 km. The flow divided around a light-colored kipuka and then banked against Pleistocene volcanic hills, where it was deflected to the south in a narrow lobe to the point labeled "X." The 2.5-km-wide caldera of Chinameca volcano lies across a saddle from San Miguel in this Space Shuttle image with north to the upper left.

NASA Space Shuttle image STS61C-31-47, 1986 (http://eol.jsc.nasa.gov/).
An eruption at San Miguel on September 21-23, 1787 from summit and N- and SE-flank vents produced five lava flows. Ashfall caused extensive crop damage. Other historical lava flows from San Miguel are labeled in this Space Shuttle image with north to the upper left. The 1762 lava flow (faintly seen at the upper right) extended as far as the present-day city of San Miguel. The 2.5-km-wide caldera of Chinameca volcano lies NW of San Miguel volcano, and the small dark-colored dot at the upper right is Laguna de Aramuaca maar.

NASA Space Shuttle image STS61C-31-47, 1986 (http://eol.jsc.nasa.gov/).

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.

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.

Chesner C A, Pullinger C R, Escobar C D, 2004. Physical and chemical evolution of San Miguel volcano, El Salvador. In: Rose W I, Bommer J J, Lopez D L, Carr M J, Major J J (eds), Natural Hazards in El Salvador, {Geol Soc Amer Spec Pap}, 375: 213-226.

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

Major J J, Schilling S P, Pullinger C R, Escobar C D, 2004. Debris-flow hazards at San Salvador, San Vicente, and San Miguel volcanoes, El Salvador. In: Rose W I, Bommer J J, Lopez D L, Carr M J, Major J J (eds), Natural Hazards in El Salvador, {Geol Soc Amer Spec Pap}, 375: 89-108.

Major J J, Schilling S P, Pullinger C R, Escobar C D, Chesner C A, Howell M M, 2001. Lahar-hazard zonation for San Miguel volcano, El Salvador. U S Geol Surv Open-File Rpt, 01-395: 1-14.

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.

Rodriquez L A, Watson M W, Rose W I, Branan Y K, Bluth G J S, Chigna G, Matias O, Escobar D, Carn S A, Fischer T P, 2004. SO2 emissions to the atmosphere from active volcanoes in Guatemala and El Salvador, 1999-2002. J Volc Geotherm Res, 138: 325-344.

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

Weber H S, Wiesemann G, 1978. Mapa Geologico de la Republica de El Salvador/America Central. Bundesanstalt fur Geowissenschaften und Rohstoffe, Hannover, Germany, 1:100,000 scale geologic map in 6 sheets.

Williams H, Meyer-Abich H, 1955. Volcanism in the southern part of El Salvador with particular reference to the collapse basins of Lakes Coatepeque and Ilopango. Univ Calif Pub Geol Sci, 32: 1-64.

Volcano Types

Stratovolcano

Tectonic Setting

Subduction zone
Continental crust (> 25 km)

Rock Types

Major
Andesite / Basaltic Andesite
Basalt / Picro-Basalt

Population

Within 5 km
Within 10 km
Within 30 km
Within 100 km
1,232
63,007
796,482
3,633,885

Affiliated Databases

Large Eruptions of San Miguel 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.