Report on Galeras (Colombia) — 5 April-11 April 2006
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 5 April-11 April 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, 5 April-11 April 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 that Galeras remained at a critical state during 5-10 April, with a partially solidified lava dome in the main crater. Decreases were observed in various measured parameters at the volcano, including seismicity, deformation, gas emissions, and temperatures. According to INGEOMINAS, most of the explosive eruptions at Galeras in the past 17 years occurred when parameters were at similarly low levels. In addition, the current lava dome has a significantly greater volume than the dome that was destroyed during an eruption in 1992. Also, the volume of magma in the interior of the volcanic system is greater than during 1989-1993. Galeras remained at Alert Level 2 (likely eruption in days or weeks).
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.