Based on visual observations during clear weather, INGEOMINAS reported that steam-and-gas plumes from Galeras rose to a maximum altitude of 5.3 km (17,400 ft) a.s.l. during 21-23 November and 3 December. The plumes occasionally contained small volumes of ash and were associated with seismic tremor. Gas and ash plumes that rose to an altitude of 4.4 km (14,400 ft) a.s.l. and drifted NW were observed during an overflight on 27 November. Thermal images indicated an increase in temperatures since a 2 October overflight at the point sources of emissions. 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)