Report on San Miguel (El Salvador) — January 1986
Scientific Event Alert Network Bulletin, vol. 11, no. 1 (January 1986)
Managing Editor: Lindsay McClelland.
San Miguel (El Salvador) Ash emission and seismicity
Please cite this report as:
Global Volcanism Program, 1986. Report on San Miguel (El Salvador). In: McClelland, L. (ed.), Scientific Event Alert Network Bulletin, 11:1. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198601-343100.
13.434°N, 88.269°W; summit elev. 2130 m
All times are local (unless otherwise noted)
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.
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: José González and Salvador Jesus, Dept de Sismología, Centro de Investigaciones Geotécnicas, San Salvador, El Salvador; David Harlow, USGS.