Report on San Miguel (El Salvador) — March 1995
Bulletin of the Global Volcanism Network, vol. 20, no. 3 (March 1995)
Managing Editor: Richard Wunderman.
San Miguel (El Salvador) Increased seismicity and minor ashfall near the crater
Please cite this report as:
Global Volcanism Program, 1995. Report on San Miguel (El Salvador). In: Wunderman, R. (ed.), Bulletin of the Global Volcanism Network, 20:3. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199503-343100.
13.434°N, 88.269°W; summit elev. 2130 m
All times are local (unless otherwise noted)
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 (10 km NE) has a population of ~150,000, and the rural zone that would likely be affected has a population of ~100,000.
Geologic Background. 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 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, 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 N, NE, and SE sides. The SE-flank 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.
Information Contacts: Jorge Alberto Rodríguez Deras, Director, Centro de Investigaciones Geotécnicas, San Salvador, El Salvador.