IG reported a high level of activity at Sangay during 21-28 December. Seismicity was characterized by daily explosions, long-period earthquakes, and signals indicating emissions. Weather clouds and rain sometimes prevented visual and webcam observations of the volcano, though almost daily ash-and-gas plumes were identified in satellite images by the Washington VAAC or in webcam views; plumes rose as high as 1.5 km above the volcano and drifted SE, S, SW, and W. Multiple (33-73 per day) daily thermal anomalies over the volcano were visible in satellite data. On 25 December volcano observers near Macas reported hearing noises coming from Sangay, possibly due to favorable weather conditions, though the intensity of explosions had slightly increased. Crater incandescence and an active lava flow on the SE flank were visible at night during 27-28 November.

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)