Report on Santa Ana (El Salvador) — 24 August-30 August 2005
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 24 August-30 August 2005
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2005. Report on Santa Ana (El Salvador). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 24 August-30 August 2005. Smithsonian Institution and US Geological Survey.
13.853°N, 89.63°W; summit elev. 2381 m
All times are local (unless otherwise noted)
SNET reported a significant increase in seismic activity at Santa Ana (also called Ilamatepec) on the night of 27 August. A cluster of 17 volcano-tectonic earthquakes were recorded, with four located S of the volcano. Afterwards, continuous high-frequency tremor was recorded until at least 30 August. Observations made on 29 August revealed incandescent rocks in the fumarole field. The incandescence was due to the hot gases emitted from the fumaroles heating the rocks. A significant increase in sulfur-dioxide emission was recorded, and gas-and-steam plumes rose 500-1,000 m above the volcano's crater (or 9,400-11,000 ft a.s.l.). As a safety measure, access to the volcano's crater was restricted to visitors.
Prior to the current increase in activity, strong degassing had been measured at the volcano since June 2004. An ash emission occurred on 16 June 2005, and a slight increase in seismicity and a significant increase in gas emission was measured from 27 July until at least 30 August.
Geologic Background. Santa Ana, El Salvador's highest volcano, is a massive, dominantly andesitic-to-trachyandesitic stratovolcano that rises immediately W of Coatepeque caldera. Collapse of Santa Ana (also known as Ilamatepec) during the late Pleistocene produced a voluminous debris avalanche that swept into the Pacific Ocean, forming the Acajutla Peninsula. Reconstruction of the volcano subsequently filled most of the collapse scarp. The broad summit is cut by several crescentic craters, and a series of parasitic vents and cones have formed along a 20-km-long fissure system that extends from near the town of Chalchuapa NNW of the volcano to the San Marcelino and Cerro la Olla cinder cones on the SE flank. Historical activity, largely consisting of small-to-moderate explosive eruptions from both summit and flank vents, has been documented since the 16th century. The San Marcelino cinder cone on the SE flank produced a lava flow in 1722 that traveled 13 km E.