Servicio Nacional de Estudios Territoriales (SNET) reported that during a survey of the San Miguel crater on 9 and 16 March observers noted pulses of gas rising 200 m from the crater. On 12 March the number and amplitude of earthquakes increased. RSAM values rose the next day to 121 units per day on average, up from normal values around 50 units per day. RSAM values continued to fluctuate during the next few days and reached as high as 319 units on 19 March, 414 units on 20 March, and 234 on 21 March. On 18 and 20 March, local residents felt vibrations and heard minor rumbling. Observations on 25 March indicated that gas plumes rose 100 m from the crater. On 28 March SNET noted that seismicity had gradually decreased during the previous few days, and was as low as 80 RSAM units on 27 March. Access to areas within a 2-km-radius remained restricted.

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)