Report on Galeras (Colombia) — 2 February-8 February 2011
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 2 February-8 February 2011
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2011. Report on Galeras (Colombia) (Sennert, S, ed.). Weekly Volcanic Activity Report, 2 February-8 February 2011. Smithsonian Institution and US Geological Survey.
1.22°N, 77.37°W; summit elev. 4276 m
All times are local (unless otherwise noted)
On 8 February, INGEOMINAS reported that "tornillo-type" earthquakes from Galeras had not been detected since 5 February. Seismic levels continued to fluctuate. On 6 February an overflight revealed that gas emissions had increased in comparison to the previous week, forming plumes that drifted NW. The Alert Level was lowered to III (Yellow; "changes in the behavior of volcanic activity").
Geological Summary. 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 open 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 eruptions since the time of the Spanish conquistadors.