Report on Galeras (Colombia) — 11 March-17 March 2009
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 11 March-17 March 2009
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2009. Report on Galeras (Colombia). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 11 March-17 March 2009. 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 an explosive eruption from Galeras that began at 1555 on 13 March; the Alert Level was raised from II (Orange; "probable eruption in term of days or weeks") to I (Red; "imminent eruption or in progress"), on a scale of 4-1. Inclement weather prevented direct observations of the volcano. The Washington Volcanic Ash Advisory Center (VAAC) indicated that a plume rose to an altitude of 12.3 km (40,400 ft) a.s.l. and drifted NW. The eruption produced sounds heard in areas 10 km E and W. Ashfall was reported in multiple areas E and NW; a sulfur odor was also reported in some areas. On 14 March, gas plumes with some ash content rose to an altitude of 6.3 km (20,700 ft) a.s.l. The Alert Level was lowered to back to II.
According to news articles, authorities ordered the evacuation of about 8,000 people living in high-risk areas, but few went to evacuation shelters.
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.