Report on Galeras (Colombia) — 9 December-15 December 2009
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 9 December-15 December 2009
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2009. Report on Galeras (Colombia). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 9 December-15 December 2009. Smithsonian Institution and US Geological Survey.
1.22°N, 77.37°W; summit elev. 4276 m
All times are local (unless otherwise noted)
INGEOMINAS reported that observations of Galeras during an overflight on 3 December revealed thermal anomalies in the main crater measuring 155 degrees Celsius. During 8-11 December, seismic activity decreased, although some seismic signals resembled patterns seen prior to previous eruptions. Sulfur dioxide emissions were low. Seismicity increased on 12 December; earthquakes M 2.2 and less were detected within 2 km of the summit and at depths up to 3 km below the summit during 12-15 December. The Alert Level was raised to II (Orange; "probable eruption in term of days or weeks").
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.