Global Volcanism Program

23 March-29 March 2011

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.

Sources: Servicio Nacional de Estudios Territoriales (SNET)

Available Weekly Reports

23 March 2011 Back to Top

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.

Sources: Servicio Nacional de Estudios Territoriales (SNET)

11 August 2010 Back to Top

On 13 August, Servicio Nacional de Estudios Territoriales (SNET) reported that seismicity remained above background levels after an increase was detected on 1 August. Average background RSAM values ranged from 15 to 50 units per day. During 12-13 August, RSAM values ranged between 433 and 465. Over the next few days, seismicity decreased significantly; from 14 August to 16 August, RSAM values decreased from 188 to 132. Access to areas within a 2-km-radius remained restricted.

Sources: Servicio Nacional de Estudios Territoriales (SNET)

15 July 2009 Back to Top

On 20 July, Servicio Nacional de Estudios Territoriales (SNET) reported that the amplitude of seismic events from San Miguel had decreased to normal or background levels. Access to areas within a 2-km-radius continued to be restricted.

Sources: Servicio Nacional de Estudios Territoriales (SNET)

8 July 2009 Back to Top

Servicio Nacional de Estudios Territoriales (SNET) reported that the amplitude of seismic events from San Miguel had decreased during 9-13 July, but RSAM values remained above the background average. Access to areas within a 2-km-radius was restricted.

Sources: Servicio Nacional de Estudios Territoriales (SNET)

1 July 2009 Back to Top

Servicio Nacional de Estudios Territoriales (SNET) reported that seismic amplitude from San Miguel increased for a period of time between 0500 and 1400 on 6 July. Seismicity remained elevated above background levels on 7 July.

Sources: Servicio Nacional de Estudios Territoriales (SNET)

11 October 2006 Back to Top

Servicio Nacional de Estudios Territoriales (SNET) reported on 10 October that an Alert Level for San Miguel was established as Green within 4 km from the center of the crater due to a slight increase in seismic activity. On 15 October, the Alert Level was increased to Yellow due to further increases in seismic activity, but then decreased to Green again the next day.

Sources: Servicio Nacional de Estudios Territoriales (SNET)

12 October 2005 Back to Top

SNET reported that activity had not changed at San Miguel after small clusters of earthquakes occurred at the volcano during 27 September to about 14 October. During a visit to the volcano on 13 October small rockfalls were seen, but there were no significant changes in the crater and sulfur-dioxide emissions were very weak.

Sources: Servicio Nacional de Estudios Territoriales (SNET)

11 February 2004 Back to Top

According to a news article, a tectonic earthquake near San Miguel on the evening of 8 February caused landslides within the crater and on the volcano's flanks. One of the landslides threatened retention walls in the community of Carretos near the volcano. Citizens feared that heavy rains in the future could mix with the landslide material and overload the retention walls, causing them to fail.

Sources: La Prensa Grafica

30 October 2002 Back to Top

A news report stating that a rockslide released dangerous fumes at San Miguel on 17 October was found to be false.

Sources: Associated Press

23 October 2002 Back to Top

A news report stating that a rockslide released dangerous fumes at San Miguel on 17 October was found to be false.

Sources: Associated Press

Summary of eruption dates and Volcanic Explosivity Indices (VEI).

Start Date	Stop Date	Eruption Certainty	VEI	Evidence	Activity Area or Unit
2002 Jan 16	2002 Jan 16	Confirmed	1	Historical
1997 Dec 31	Unknown	Confirmed	1	Historical
1995 Jan 12	1995 Apr 19	Confirmed	1	Historical
1985 Nov	1986 Feb (in or after)	Confirmed	1	Historical
1976 Dec 2	1977 Mar 1	Confirmed	1	Historical
1970 Mar 30	1970 Apr 5	Confirmed	1	Historical
1967 Jan 5	Unknown	Confirmed	2	Historical
1966 Jul	Unknown	Confirmed	2	Historical
1966 Feb 22	Unknown	Confirmed	2	Historical
1964 Oct 23	1964 Nov	Confirmed	2	Historical
1954 Oct 21	1954 Oct 21	Confirmed	2	Historical
1939 May	1939 Jul	Confirmed	2	Historical
[ 1936 (?) ]	[ Unknown ]	Uncertain	2
1931 Mar	1931 Jun	Confirmed	2	Historical
1930 Jan 26 ± 5 days	Unknown	Confirmed	2	Historical
1929 Aug	Unknown	Confirmed	2	Historical
1920 Aug 14	1925	Confirmed	2	Historical
1919 Dec 10	1920 Jan	Confirmed	2	Historical
1890	1891	Confirmed	2	Historical
1884 Jan 25	1884 Jan 28 ± 1 days	Confirmed	2	Historical	NE side of main crater
1882 Dec 5 ± 4 days	Unknown	Confirmed	2	Historical
1867 Dec 14	1868 Feb 16 (in or after)	Confirmed	2	Historical	WSW flank (1000 m)
1862 Jan	Unknown	Confirmed	2	Historical
1857 Nov	Unknown	Confirmed	2	Historical
1855 Dec	Unknown	Confirmed	2	Historical	SSE flank (800 m)
[ 1854 ]	[ Unknown ]	Uncertain	2
1844 Jul 25	1848	Confirmed	2	Historical	NNW (1120 m) and upper east flanks
1819 Jul 18	Unknown	Confirmed	2	Historical	SSE flank (400 m; near Los Perolitos)
[ 1811 ]	[ Unknown ]	Uncertain	2
[ 1798 (?) ]	[ Unknown ]	Uncertain	2
1787 Sep 21	1787 Sep 23	Confirmed	2	Historical	Summit, north and SE flanks
1769	Unknown	Confirmed	2	Historical	East flank ?
1762	Unknown	Confirmed	2	Historical	NE flank (400 m)
1699	Unknown	Confirmed	2	Historical	SE flank (400 m)
1510 ± 5 years	Unknown	Confirmed		Historical

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 of the 2130-m-high volcano 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 of the towering volcano, which is 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 north, NE, and SE sides. The SE-flank lava 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.