INGEOMINAS reported that on 29 April an eruption from Galeras was detected by the seismic network. Observers to the N and NW reported that an ash plume drifted NW; ash fell in areas up to 35 km downwind. During 4-5 May, ash plumes drifted NE and ashfall was reported in multiple areas of Pasto (about 10 km E). The Alert Level remained at II (Orange; "probable eruption in term of days or weeks").

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)