On 30 October, INGEOMINAS reported that the Alert Level for Galeras was raised to II (Orange; "probable eruption in term of days or weeks"). Since 27 October, degassing decreased and seismicity increased, reflecting conditions seen prior to previous eruptions. On 3 November, INGEOMINAS stated that gas emissions had been low during the previous days, and seismicity had decreased that day.

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)