Report on Galeras (Colombia) — 18 May-24 May 2005
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 18 May-24 May 2005
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2005. Report on Galeras (Colombia). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 18 May-24 May 2005. Smithsonian Institution and US Geological Survey.
1.22°N, 77.37°W; summit elev. 4276 m
All times are local (unless otherwise noted)
According to a news article, on 24 May the Colombian government ordered the evacuation of ~9,000 people living near Galeras due to an increase in volcanic activity. INGEOMINAS reported that during 16-23 May, small shallow earthquakes occurred beneath the volcano. There was an increase in earthquakes associated with fracturing within the volcano during the night of 21 May to the morning of 22 May. Gas emissions slightly decreased on 17 and 20 May in comparison to 29 April and 2 May, and slightly increased around 23 May. Deformation continued to be recorded at the volcano's summit. There were no ash emissions. Galeras remained at Alert Level 2 (probable eruption in terms of days or weeks) as it has since 19 April 2005.
Geologic Background. Galeras, a stratovolcano with a large breached caldera located immediately west of the city of Pasto, is one of Colombia's most frequently active volcanoes. The dominantly andesitic complex has been active for more than 1 million years, and two major caldera collapse eruptions took place during the late Pleistocene. Long-term extensive hydrothermal alteration has contributed to large-scale edifice collapse on at least three occasions, producing debris avalanches that swept to the west and left a large horseshoe-shaped caldera inside which the modern cone has been constructed. Major explosive eruptions since the mid-Holocene have produced widespread tephra deposits and pyroclastic flows that swept all but the southern flanks. A central cone slightly lower than the caldera rim has been the site of numerous small-to-moderate historical eruptions since the time of the Spanish conquistadors.