Report on Galeras (Colombia) — February 1994
Bulletin of the Global Volcanism Network, vol. 19, no. 2 (February 1994)
Managing Editor: Richard Wunderman.
Galeras (Colombia) Numerous rock-fracture events, but other seismicity remains low
Please cite this report as:
Global Volcanism Program, 1994. Report on Galeras (Colombia) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 19:2. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199402-351080.
1.22°N, 77.37°W; summit elev. 4276 m
All times are local (unless otherwise noted)
Seismic activity stayed at low levels in February (0-4 events/day); however, small variations in background tremor amplitude were noted. A large number of relatively small seismic events (2,810) were associated with rock fractures and fluid movement near the cone. There were a few rock-fracture events centered NNE of the crater. These "butterfly-type events" appear to be influenced by the gravitational field associated with the tides and by other external agents such as rain. No deformation changes were detected by E-flank electronic tiltmeters 0.9 and 1.6 km from the summit. Degasification was concentrated in the W sector of the cone at the "La Chava" and "Florencia" craters. SO2 flux, measured by COSPEC 15 times in January-Feb, stayed below 240 t/d, except on 15 February when it was ~480 t/d.
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: INGEOMINAS, Pasto.