INGEOMINAS reported an explosive eruption from Galeras that began at 0705 on 20 February; the Alert Level was raised from II (Orange; "probable eruption in term of days or weeks") to I (Red; "imminent eruption or in progress"), on a scale of 4-1. The eruption was accompanied by shock waves detected in several local communities and produced sounds heard in Popayán (about 160 km NNE). Observers from areas on the E flank reported two explosions, incandescent blocks ejected above the summit, ash emissions, and sulfur gas odor. An ash plume rose to an altitude of 12.5 km (41,000 ft) a.s.l. and drifted E, W, and N. Ashfall was reported in areas to the W. Gas plumes with a low ash content continued, especially in the afternoon, and rose 700 m above the summit. On 21 February, the Alert Level was lowered to back to II. During 22-24 February, occasional steam plumes rose 500 m above the summit and drifted NNW.

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)