MARN reported that an eruption at San Miguel’s central crater began on 15 November, and by 1100 on 20 November a total of 62 phreatic explosions had been recorded, averaging 10 per day. An additional 24 explosions were recorded from 1100 on 20 November to 1100 on 21 November and 12 more were recorded between 1100 and 1100 during 21-22 November. Explosions generated gas, ash, and steam plumes that generally rose around 500 m above the crater rim, though at 1336 on 18 November and 1206 on 19 November eruption plumes rose as high as 1.1 km. Some of the events were accompanied by crater incandescence during 15-20 November. Sulfur dioxide emissions generally averaged 100-170 tons per day, below the baseline of 300 tons per day. Specific measurements during explosive events revealed that the emissions were sometimes higher; 1,200 tons per day was measured on 19 November during one of the largest explosions, and 378 tons per days was measured during an explosion on 21 November. Seismicity was characterized by volcano-tectonic events, long-period events, and tremor. Deformation data showed no significant changes. The public was warned to stay 2 km away from the volcano, and for those living within a 2-5 km radius to identify evacuation routes and to take preparation measures as guided by the Sistema Nacional de Protección Civil.

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.

Source: Ministerio de Medio Ambiente y Recursos Naturales (MARN)