INGEOMINAS reported that volcanic and seismic activity increased at Galeras on 11 August at 2349 when an eruption began that sentan ash-and-gas cloud to an unknown height and generated visible incandescence. According to the Washington VAAC, satellite imagery showed that an ash plume rose to a height of ~10.7 km a.s.l. It spread in all directions, but mainly to the NE, E, and SW. Later in the day, a thin plume at a height of ~7.3 km a.s.l drifted SW into northern Ecuador. A plume also drifted NW at a height of ~6.1 km a.s.l. By 1315 ash was no longer visible on satellite imagery. Fine ash was deposited in villages near the volcano including, La Florida (~10 km NW of the volcano), Nariño, Sandoná, and Consacá, and farther afield in Ancuya, Linares, and Sotomayor (~ 40 km NW of the volcano).

News articles reported that ~230 families were evacuated mainly from the volcano's N flank. Ash contaminated potable water in some villages, impacted farm animal's health, and left hundreds of dead fish floating in rivers. The village of La Florida was most strongly impacted by the eruption. On 16 August, ash emissions continued, depositing ash in several villages. A thin plume was visible on satellite imagery extending ~75 km NW.

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), EL PAÍS, El Spectador