Report on Galeras (Colombia) — 11 February-17 February 2009
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 11 February-17 February 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 February-17 February 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 1910 on 14 February; the Alert Level was raised from III (Yellow; "changes in the behavior of volcanic activity") to I (Red; "imminent eruption or in progress"), on a scale of 4-1. An accompanying shock wave was detected in multiple areas, including in parts of Pasto (about 10 km E). The altitude of the resultant ash plume was not known nor observed on satellite images due to cloud cover. From about 1930 until 2030 ashfall, rain, and an odor of sulfur gas were reported on the slopes of the volcano as well as in Pasto. Ash deposits were mainly in areas to the E and as far away as 25 km. Seismicity returned at 1950 to similar levels recorded prior to the eruption and remained low. On 16 February, the Alert Level was lowered to II (Orange; "probable eruption in term of days or weeks"). During 16-17 February, small steam plumes rose to altitudes of 4.6-6.7 km (15,100-22,000 ft) a.s.l. and drifted SE, E, and NE.
According to news articles, authorities ordered the evacuation of about 8,000 people living on the slopes, 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.