Report on Galeras (Colombia) — 18 July-24 July 2012
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 18 July-24 July 2012
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2012. Report on Galeras (Colombia). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 18 July-24 July 2012. 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 during 18-24 July earthquakes at Galeras were less than M 1.3 and located at depths not exceeding 3 km. Gas emissions, observed by a network of video cameras, contained ash almost daily. Sulfur dioxide levels fluctuated. On 18 July observatory staff working near the crater reported a strong sulfur odor and fine ash falling on the upper N flank. Ashfall was also reported to the N in the Quebrada Maragato area (municipality of Nariño). The Alert Level remained at 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.