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Report on Galeras (Colombia) — January 1990


Bulletin of the Global Volcanism Network, vol. 15, no. 1 (January 1990)
Managing Editor: Lindsay McClelland.

Galeras (Colombia) Ash emission and increased seismicity; earthquake swarm 3-5 km W of the crater

Please cite this report as:

Global Volcanism Program, 1990. Report on Galeras (Colombia) (McClelland, L., ed.). Bulletin of the Global Volcanism Network, 15:1. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199001-351080



1.22°N, 77.37°W; summit elev. 4276 m

All times are local (unless otherwise noted)

The number of high- and low-frequency earthquakes increased in January (see figure 18). Pulses of spasmodic tremor accompanied ash emission on the 7th. A swarm of high-frequency events occurred W of the crater at depths of 3-5 km on the 10th (figure 14). The electronic tiltmeter showed an increase of 3 µrad on 26 January, coinciding with an M 2 earthquake beneath the tiltmeter station. Gas emission was not measured in January.

Figure (see Caption) Figure 14. Epicenters of 95 seismic events near Galeras, January 1990. Courtesy of INGEOMINAS.

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, Pasto; INGEOMINAS, Manizales.