SNET reported that local observers of San Miguel reported a series of rumbling noises that occurred from 1900 on 20 February to 0750 on 21 February. The report noted an increase in amplitude of microearthquakes and minor gas emissions form the main crater. Sulfur dioxide levels had also increased. Beginning at 1055 on 22 February an ash emission that lasted 10 minutes long resulted in a small gas-and-ash plume that rose 400 m above the crater rim. Minor ashfall was reported in the area of Piedra Azul, 5 km SW. RSAM peaked at 510 units during the period of emissions, above the normal values of 150, as recorded by station VSM located on the upper N flank. The number of low-amplitude tremor events increased after a quiet period of about 11 hours and were associated with gas emissions; RSAM was 33-97 units and minor gas plumes were visible rising 400 m during 23-24 February.

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: Servicio Nacional de Estudios Territoriales (SNET)