Report on Galeras (Colombia) — 17 September-23 September 2008
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 17 September-23 September 2008
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2008. Report on Galeras (Colombia). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 17 September-23 September 2008. 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 incandescence was observed in Galeras's crater during an overflight on 19 September. Thermal images revealed a significant anomaly from the cone in the main crater that measured 550 degrees Celsius; other anomalies on the sides of the cone measured 270 degrees Celsius. Sulfur dioxide values were near 8,200 tonnes. Further measurements during 19-23 September revealed temperatures between 500 and 600 degrees Celsius and sulfur dioxide values between 3,000 and 5,200 tonnes.
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.