INGEOMINAS reported that during 4-5 October, steam plumes from Galeras rose to altitudes of 5.8-6.3 km (19,000-20,700 ft) a.s.l. Occasional pulses of ash accompanied the steam emissions. Plumes drifted N and NW. The Alert Level remained at 3 (changes in the behavior of volcanic activity have been noted) on a scale of 4-1.

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.

Source: Servicio Geológico Colombiano (SGC)