INGEOMINAS reported that on 17 May ash emissions originating from an area N and W of the cone within Galeras's main crater rose 200 m above the crater rim. During 26-27 May ash plumes rose 800 m above the crater; ashfall was reported in Sandona (13 km NW). Ash emissions occurred on 2 June, and on 5 June plumes rose 1 km and drifted W. The Alert Level remained at III (Yellow; "changes in the behavior of volcanic activity").

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.

Sources: Washington Volcanic Ash Advisory Center (VAAC), Servicio Geológico Colombiano (SGC)