Report on Galeras (Colombia) — 30 November-6 December 2011
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 30 November-6 December 2011
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2011. Report on Galeras (Colombia). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 30 November-6 December 2011. 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 29 November revealed thermal analomies in the main crater. During an overflight on 6 December scientists observed that gas emissions rose from the main crater and two craters to the N and SW (Paisita and Chavas, respectively) and had increased in comparison to the previous week. Thermal anomalies were also detected in the main crater. INGEOMINAS raised the Alert Level to III (Yellow; "changes in the behavior of volcanic activity") on 6 December.
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.