Report on Galeras (Colombia) — May 1990
Bulletin of the Global Volcanism Network, vol. 15, no. 5 (May 1990)
Managing Editor: Lindsay McClelland.
Galeras (Colombia) Earthquake swarm but no ash emissions
Please cite this report as:
Global Volcanism Program, 1990. Report on Galeras (Colombia) (McClelland, L., ed.). Bulletin of the Global Volcanism Network, 15:5. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199005-351080
1.22°N, 77.37°W; summit elev. 4276 m
All times are local (unless otherwise noted)
Activity was at a low level during May, with no observed ash emissions or morphologic changes in the crater. A high-frequency earthquake swarm occurred on 4-5 May with magnitudes <=2.2. On 27 May, 3 June, and 6 June, single high-frequency earthquakes felt by flank residents had magnitudes of 3.0, 3.05, and 3.2 respectively, and depths ranging between 2.5 and 6.0 km. The swarm events and the felt earthquakes were centered 2 km W of the crater, one of the loci of seismic activity during April (15:4). The number and intensity of low-frequency earthquakes and tremor remained at normal levels. No significant changes in ground deformation were recorded.
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.