Report on Galeras (Colombia) — November 1992
Bulletin of the Global Volcanism Network, vol. 17, no. 11 (November 1992)
Managing Editor: Lindsay McClelland.
Galeras (Colombia) Low-level seismicity, gas emission, and deformation
Please cite this report as:
Global Volcanism Program, 1992. Report on Galeras (Colombia) (McClelland, L., ed.). Bulletin of the Global Volcanism Network, 17:11. Smithsonian Institution.
1.22°N, 77.37°W; summit elev. 4276 m
All times are local (unless otherwise noted)
Seismicity, gas emission, and deformation were generally at low levels during November, although a swarm of 22 long-period events was recorded on the 10th. Most of the month's seismicity was thought to be associated with movement of fluids. Rock-breakage events were less frequent than in October, and were centered E of the active crater. Tremor episodes remained at low energy levels, with maximum durations and amplitudes of 287 seconds and 3.2 mm, respectively. SO2 flux measured by COSPEC ranged from 46 to 547 t/d, similar to October values.
Tilt data from [Crater Station] showed 6 µrad of deflation in November. A second station, 1.6 km E of the crater, measured 6 µrad of inflation during the first half of the month. A 40-µrad change registered by its tangential component during the second half of November may have been caused by local movements at the site.
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.
Information Contacts: F. Muñoz, INGEOMINAS—Observatorio Vulcanológico del Sur.