IG reported a high level of activity at Sangay during 18-25 October. Daily seismic counts ranges were 230-734 explosions, 39-86 tremor events indicating emissions, and 1-2 lahar events; 10-23 long-period events were recorded during 22-23 October. Daily ash-and-gas plumes were identified in IG webcam images and/or visible in satellite images according to the Washington VAAC. Plumes generally rose as high as 2.1 km above the volcano and drifted NW, W, and SW. Almost daily thermal anomalies were identified in satellite images, though weather clouds sometimes prevented views. Sulfur dioxide emissions averaged 363-1,716 tons per day during 18-25 October. Incandescence at the summit and from a new lava flow on the SE flank was visible during 18-19 October; incandescence from lava-flow activity continued to be periodically visible the rest of the week. Servicio Nacional de Gestión de Riesgos y Emergencias lowered the Alert Level to Yellow (on a four-color scale) during 20-21 October.

Geological Summary. The isolated Sangay volcano, located east of the Andean crest, is the southernmost of Ecuador's volcanoes and its most active. The steep-sided, glacier-covered, dominantly andesitic volcano grew within the open calderas of two previous edifices which were destroyed by collapse to the east, producing large debris avalanches that reached the Amazonian lowlands. The modern edifice dates back to at least 14,000 years ago. It towers above the tropical jungle on the east side; on the other sides flat plains of ash have been eroded by heavy rains into steep-walled canyons up to 600 m deep. The earliest report of an eruption was in 1628. Almost continuous eruptions were reported from 1728 until 1916, and again from 1934 to the present. The almost constant activity has caused frequent changes to the morphology of the summit crater complex.

Source: Instituto Geofísico-Escuela Politécnica Nacional (IG-EPN)