Report on Galeras (Colombia) — 1 June-7 June 2005
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 1 June-7 June 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, 1 June-7 June 2005. Smithsonian Institution and US Geological Survey.
1.22°N, 77.37°W; summit elev. 4276 m
All times are local (unless otherwise noted)
During 30 May to 6 June, there was a decrease in seismicity and deformation at Galeras in comparison to the previous week. The number and magnitude of earthquakes decreased and there were smaller changes in deformation. The level of alert was decreased from 2 (probable eruption in days or weeks) to 3 (changes in the behavior of volcanic activity have been noted).
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.