Report on Galeras (Colombia) — 22 April-28 April 2009
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 22 April-28 April 2009
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2009. Report on Galeras (Colombia) (Sennert, S, ed.). Weekly Volcanic Activity Report, 22 April-28 April 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 that on 24 April seismicity from Galeras was similar to that seen prior to previous eruptions. Video camera views of the crater showed decreased gas emissions. The Alert Level was raised to II (Orange; "probable eruption in term of days or weeks"). Later that day, an explosive eruption was detected, prompting INGEOMINAS to raise the Alert Level to I (Red; "imminent eruption or in progress"). Incandescent blocks caused fires on the N flank. An accompanying shock wave was reported by residents up to 25 km away. A second eruption, of greater duration but less energy than the first, was detected about a half an hour later. Incandescence from both eruptions was seen from the city of Pasto (10 km E). An ash plume rose to an altitude of 10.3 km (33,800 ft) a.s.l. Ashfall was reported in areas up to 20 km W, WNW, and NW. According to a news article, populations living near the volcano were ordered to evacuate; about 200 people responded. On 25 April, ash-and-gas plumes rose 1 km above the crater. Thermal anomalies in the crater near the W flank measured 100 degrees Celsius. Ejected rocks had landed 2-3 km from the crater. The Alert Level was lowered to II.
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 open 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 eruptions since the time of the Spanish conquistadors.