Report on Galeras (Colombia) — 12 April-18 April 2006
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 12 April-18 April 2006
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2006. Report on Galeras (Colombia). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 12 April-18 April 2006. 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 Galeras remained at a critical state during 10-17 April, with a partially solidified lava dome in the main crater. Seismicity continued to decrease, with an average of 70 small earthquakes occurring at the beginning of the report week, and an average of 45 occurring at the end of the week. In addition, there were small gas emissions from the volcano. Galeras remained at Alert Level 2 (likely eruption in days or weeks).
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.