INGEOMINAS reported that during 22-23 June gas plumes rising from Galeras contained some ash. An overflight on 23 June revealed that temperatures in the main crater measured between 60 and 120 degrees Celsius, except for a small zone where the temperature measured 220 degrees Celsius. Gas emissions originated from the periphery of the main crater. On 26 June, seismicity similar to that seen prior to previous eruptions, along with low rates of gas emissions, prompted INGEOMINAS to raise the Alert Level to II (Orange; "probable eruption in term of days or weeks").

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)