Wednesday, Jan 23, 2013
Small volcanic quakes and weak tremor are visible at the seismogram, but within normal levels for this active volcano. [more]
Thursday, Mar 22, 2012
The Mexican 7.4 magnitude earthquake near Acapulco on Tuesday might have affected the currently dormant San Salvador volcano in 1000 km distance and triggered an earthquake swarm under the volcano. ... [more]
San Salvador volcanoSan Salvador volcano is a massive stratovolcano immediately northwestwest of El Salvador city. Its modern summit cone is also called the Boqueron stratovolcano. It formed within a 6 km wide caldera left by the collapse of the predecessor volcano about 40,000 years ago. Remnants of the caldera rim form the Picacho and Jabalí peaks.
Boqueron volcano is truncated by a steep-walled, 500 m deep and 1500 m wide summit crater, which formed during a large eruption about 800 years ago. Before the last eruption in 1917, the crater of Boqueron contained a 400 m wide lake, which was replaced by a small, 30 m high young cinder cone, called Boqueroncito, built during the eruption along with a major lava flow on the north flank.
Most historical eruptions from San Salvador originated from flank vents.
Background:The San Salvador or Quezaltepeque volcanic center formed in the southern part of the main graben of El Salvador and is dominantly andesitic. 3 fracture zones that extend beyond the base of San Salvador volcano have been the locus for numerous flank eruptions, including 2 that formed maars on the WNW and SE sides.
Most of the 4 historical eruptions recorded since the 16th century have originated from flank vents, including two eruptions in the 17th century from the NW-flank cone of El Playón, during which explosions and a lava flow damaged inhabited areas.
A small seismic swarm occurred in August 1999, when volcano-tectonic earthquakes about 5 km from the crater were detected. No other signs of unrest were noted.
The last eruption of San Salvador volcano began on 6 June 1917 following strong and destructive earthquakes lasting for 2 hours. The eruption consisted of an effusive fissure eruption on the NW flank followed by a moderately explosive summit eruption (similar, but smaller in scale, to the Eyafjallajökull eruption in 2010).
The effusive phase produced a large aa lava flow on the NW flank, left a row of cinder cones on the eruptive fissure, and lasted about a week. The second phase started simultaneously with the waning of the waning of the first phase from a fissure vent inside the summit crater. It quickly evaporated a former 400 m wide lake and built the small Boqueroncito cinder cone. ...more