Report on Galeras (Colombia) — 28 December-3 January 2006
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 28 December-3 January 2006
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2005. Report on Galeras (Colombia). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 28 December-3 January 2006. Smithsonian Institution and US Geological Survey.
1.22°N, 77.37°W; summit elev. 4276 m
All times are local (unless otherwise noted)
During 23 December to 2 January, Galeras emitted gas and small amounts of ash. On the 23rd, four events produced ash plumes that rose to ~3 km above the volcano (or 23,900 ft a.s.l.) and drifted toward the sector of Consacá, ~13 km WSW. A cluster of 33 volcano-tectonic earthquakes occurred beneath the volcano's crater during 29-30 December. The earthquakes reached a maximum magnitude of 1.2. The sulfur-dioxide flux at the volcano varied between 300 and 1,500 tons per day. Galeras remained at Alert Level 3 ("changes in the behavior of volcanic activity have been noted").
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.