Report on Galeras (Colombia) — 3 June-9 June 2009
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
3 June-9 June 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, 3 June-9 June 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 an eruption of Galeras on 7 June was preceded by a M 4 earthquake located about 3 km SSE of the crater at a depth of 2 km, and felt by nearby residents. The eruption produced an ash plume that rose to an altitude of 6.8 km (22,300 ft) a.s.l. and drifted NW. Vibrations from an accompanying acoustic wave were detected by residents. Ashfall was reported in areas downwind. The Alert Level was raised to I (Red; "imminent eruption or in progress"). On 8 June, two explosions about 5 minutes apart were heard by people up to 45 km away. The event was preceded by an M 3.9 earthquake located 1 km E at a depth near 2 km. Ashfall was reported in areas to the NW, up to 180 km away. Based on analysis of satellite imagery, the Washington VAAC reported that the ash plume rose to an altitude of 10 km (33,000 ft) a.s.l. and drifted NW. They also reported that a second and larger eruption produced an ash plume that rose to an altitude of 13.7 km (45,000 ft) a.s.l. and drifted SE. On 9 June, INGEOMINAS reported that seismicity and sulfur dioxide output were low, and that clear conditions revealed no emissions.
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.