Report on Galeras (Colombia) — October 1990
Bulletin of the Global Volcanism Network, vol. 15, no. 10 (October 1990)
Managing Editor: Lindsay McClelland.
Galeras (Colombia) Ash emitted; seismicity declines slightly
Please cite this report as:
Global Volcanism Program, 1990. Report on Galeras (Colombia) (McClelland, L., ed.). Bulletin of the Global Volcanism Network, 15:10. Smithsonian Institution.
1.22°N, 77.37°W; summit elev. 4276 m
All times are local (unless otherwise noted)
Seismicity decreased slightly during October. One high-frequency earthquake (M 2.8) was felt in Pasto (10 km E) on 5 October. Earthquakes were centered in distinct zones: under, NE, and E of the crater. Low-frequency earthquakes remained at low levels of occurrence and energy. Spasmodic tremor was variable, and was associated with ash emissions on 17 and 18 October.
Deformation measurements showed little change, although dry tiltmeters continued to show low levels of deformation with an inflationary trend. Electronic tilt 2 km E of the crater (Peladitos station) showed changes of 1-8 Nrad.
The SO2 flux, measured by COSPEC, decreased slightly from 2,378 t/d on 1 October, to 1,994 t/d at the end of the month.
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: INGEOMINAS-OVP.