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Report on Galeras (Colombia) — January 1992


Bulletin of the Global Volcanism Network, vol. 17, no. 1 (January 1992)
Managing Editor: Lindsay McClelland.

Galeras (Colombia) Sporadic ash emission; seismicity down from October-November peak; no new dome growth

Please cite this report as:

Global Volcanism Program, 1992. Report on Galeras (Colombia) (McClelland, L., ed.). Bulletin of the Global Volcanism Network, 17:1. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199201-351080



1.22°N, 77.37°W; summit elev. 4276 m

All times are local (unless otherwise noted)

Gas emission in January was punctuated by sporadic fine ash emission, a decrease from the intense degassing and almost continuous ash emission in September-November 1991. Sulfur accumulations were observed on the E edge of the October-November 1991 dome; no dome growth has been reported since mid-November 1991. The SO2 flux, measured by COSPEC, was at low levels.

Seismicity stablized in January, at levels somewhat higher than those recorded before the October-November 1991 peak in activity (figure 52). High-frequency earthquakes were centered around the active crater at 3.3-6.8 km depth. Long-period events, often associated with ash emissions, reached a maximum for the month on 20 January. Tremor was recorded as spasmodic pulses, most intense in the first half of the month.

Figure (see Caption) Figure 52. Daily number (top) and released energy (bottom) of earthquakes at Galeras, 27 February 1989-31 January 1992. Courtesy of INGEOMINAS.

Electronic tilt measurements [at Crater Station] showed slight deflation in January (20 µrad, N component; no change, E component), ending a trend of inflation measured since September 1990. The rate of inflation increased rapidly in August 1991, then deformation stopped in November. Deformation [at Peladitos Station] fluctuated, but suggested slight inflation during the second half of the month (8 µrad in both components).

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 open 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 eruptions since the time of the Spanish conquistadors.

Information Contacts: INGEOMINAS-Observatorio Vulcanológico del Sur.