Report on Galeras (Colombia) — February 1997
Bulletin of the Global Volcanism Network, vol. 22, no. 2 (February 1997)
Managing Editor: Richard Wunderman.
Galeras (Colombia) Shallow seismicity NNE of the active crater
Please cite this report as:
Global Volcanism Program, 1997. Report on Galeras (Colombia). In: Wunderman, R. (ed.), Bulletin of the Global Volcanism Network, 22:2. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199702-351080.
1.22°N, 77.37°W; summit elev. 4276 m
All times are local (unless otherwise noted)
Low seismicity during January and February was characterized by events NNE of the crater at depths of 2- 8 km. A source at 4-10 km depth generated 30 events with M <= 1.6 (figure 81). Long-period events remained comparatively infrequent: The average occurrence was one event/day, a trend similar to previous months.
|Figure 81. Seismicity around Galeras volcano during January and February 1997. Major towns are also shown. Courtesy of OVP-INGEOMINAS.|
Galeras deformation stations located 2, 4, and 7 km from the active crater typically inflated by 15 µrad.
Geologic Background. 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: Observatorio Vulcanologico y Sismologico de Pasto, INGEOMINAS, Carrera 31, No. 18-07 Parque Infantil, PO Box 1795, Pasto, Colombia (URL: http://mafalda.univalle.edu.co/~ovp).