During 20-27 February, seismicity continued at Galeras, with an average of 280 small earthquakes occurring per day. On 26 February seismic stations detected a cluster of earthquakes. A shallow M 4.8 volcano-tectonic earthquake was registered below the volcano at 1009, followed by 35 smaller earthquakes. Slight deformation was recorded at the volcano. A flux of about 600 metric tons of sulfur dioxide was measured per day. Steam and gas rose to ~700 m above the volcano (or 16,300 ft a.s.l.). 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)