Report on Galeras (Colombia) — 15 February-21 February 2006
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 15 February-21 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, 15 February-21 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)
During 13-20 February, seismicity continued at Galeras, with an average of about 190 small earthquakes occurring per day. A flux of about 200 metric tons of sulfur dioxide was measured daily. Steam and gas rose to ~1.1 km above the volcano (or ~17,600 ft a.s.l.) on 19 February. Incandescence was visible at parts of the lava dome. The volume of the lava dome in the main crater was approximately 1.5 times larger than when it was first observed on 13 January. Galeras remained at Alert Level 3 ("changes in the behavior of volcanic activity have been noted").
Note: It was incorrectly reported in the 8-14 February Weekly Volcanic Activity Report that on 8 February pyroclastic-flow deposits were found at Galeras. Pyroclastic-fall deposits were observed.
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.