Report on Galeras (Colombia) — 22 March-28 March 2006
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
22 March-28 March 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, 22 March-28 March 2006. Smithsonian Institution and US Geological Survey.
1.22°N, 77.37°W; summit elev. 4276 m
All times are local (unless otherwise noted)
Due to an increase in tremor at Galeras beginning on the morning of 28 March, INGEOMINAS raised the Alert Level from 3 ("changes in the behavior of volcanic activity have been noted") to 2 ("likely eruption in days or weeks"). On the 28th, energetic signals and tremor began that had been absent during previous weeks. In addition, seismic instruments detected very shallow low-energy hybrid signals, similar to ones recorded during 1991-1993 when dome emplacement occurred on the main crater's floor.
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 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.