Report on Galeras (Colombia) — 13 May-19 May 2009
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 13 May-19 May 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, 13 May-19 May 2009. Smithsonian Institution and US Geological Survey.
1.22°N, 77.37°W; summit elev. 4276 m
All times are local (unless otherwise noted)
On 19 May, INGEOMINAS reported that gas plumes from Galeras occasionally contained some ash during the previous four days. An overflight on 17 May revealed gas emissions emanating from multiple points inside and outside of the main crater. Some thermal anomalies surpassed 180 degrees Celsius. During 17-18 May, two M 2.9 earthquakes occurred 6 km SSE at depths of 2-3 km, and on 18 May one M 2.3 earthquake occurred at a depth of 3-5 km, 5 km SSW. The Alert Level was lowered to III (Yellow; "changes in the behavior of volcanic activity").
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.