Report on Galeras (Colombia) — 6 October-12 October 2004
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 6 October-12 October 2004
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2004. Report on Galeras (Colombia). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 6 October-12 October 2004. Smithsonian Institution and US Geological Survey.
1.22°N, 77.37°W; summit elev. 4276 m
All times are local (unless otherwise noted)
During 8-11 October, emissions of gas and fine ash continued at Galeras. Plumes rose to a maximum height of ~1.5 km above the volcano. Small-amplitude tremor associated with gas-and-ash emissions was recorded.
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.