Santa Ana volcano (El Salvador) - Smithsonian / USGS Weekly Volcanic Activity Report for 24 August-30 August 2005 (New Activity / Unrest)

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.

Source: Servicio Nacional de Estudios Territoriales (SNET)
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From: Global Volcanism Program, 2005. Report on Santa Ana. In: Mayberry, G (ed.), Weekly Volcanic Activity Report 24 August-30 August 2005. Smithsonian Institution and US Geological Survey.