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Report on Galeras (Colombia) — 29 July-4 August 2009


Galeras

Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 29 July-4 August 2009
Managing Editor: Sally Sennert.

Please cite this report as:

Global Volcanism Program, 2009. Report on Galeras (Colombia) (Sennert, S, ed.). Weekly Volcanic Activity Report, 29 July-4 August 2009. Smithsonian Institution and US Geological Survey.

Weekly Report (29 July-4 August 2009)

Galeras

Colombia

1.22°N, 77.37°W; summit elev. 4276 m

All times are local (unless otherwise noted)


On 4 August, INGEOMINAS reported that activity from Galeras had remained at a low level since the previous report on 28 July; the Alert Level was lowered to III (Yellow; "changes in the behavior of volcanic activity"). During the previous few days, active fumaroles were seen on the W flank of the active cone.

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.

Source: Servicio Geológico Colombiano (SGC)