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.

Geological Summary. The symmetrical cone of San Miguel, one of the most active volcanoes in El Salvador, rises from near sea level to form one of the country's most prominent landmarks. A broad, deep, crater complex that has been frequently modified by eruptions recorded since the early 16th century caps the truncated unvegetated summit, also known locally as Chaparrastique. Flanks eruptions of the basaltic-andesitic volcano have produced many lava flows, including several during the 17th-19th centuries that extended to the N, NE, and SE. 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. Flank vent locations have 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.