Report on Galeras (Colombia) — 8 February-14 February 2006
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 8 February-14 February 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, 8 February-14 February 2006. 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 on 10 February that a lava dome was growing inside the main crater of Galeras. The lava dome was not seen during the previous observation flight on 16 January. Seismicity was dominated by long-period earthquakes, with an average of 150 occurring daily during 13 January to 8 February. On 5 February, strong degassing was visible from different parts of the active cone and around the lava dome. Cracks were visible on the high parts of the lava dome. During a field visit on 8 February, scientists found fall material [originally incorrectly reported in the WVAR as pyroclastic-flow deposits] high on the SE flank of the volcano. The exact date of the small emission was not known, but it occurred after 26 November when scientists previously visited the area. Galeras remained at Alert Level 3 ("changes in the behavior of volcanic activity have been noted").
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.