On 17 July, INGEOMINAS (Instituto Colombiano de Geología y Minería) reported that after the 12 July eruption of Galeras, seismic activity decreased considerably. Observations of the dome and secondary craters in the W sector post-12 July, showed small physical changes. Gas plumes with little steam content were observed without associated seismic activity. Galeras remained at Alert Level 3 (changes in the behavior of volcanic activity have been noted).

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)