IG reported a high level of activity at Sangay during 17-23 May, though weather clouds sometimes prevented visual observations. Incandescent material at the crater and along the lava flow extending 1 km down the SE flank was visible nightly. On 17 May steam-and-ash emissions rose 500 m above the summit and drifted SW. On 18 May an ash plume rose 1.7 km and drifted N and SW. At 2000 on 20 May ash plumes rose 2 km above the summit and drifted to the SW. Continuous ash emissions persisted during 21-22 May, drifting W and SW. Ashfall during 20-22 May was reported in Chauzan, Guamote, Tixán, Palmira, Cebadas, and Alausí cantons in the Province of Chimborazo. Servicio Nacional de Gestión de Riesgos y Emergencias (SNGRE) maintained the Alert Level at Yellow (the second lowest level on a four-color scale).

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.

Sources: Instituto Geofísico-Escuela Politécnica Nacional (IG-EPN), Servicio Nacional de Gestión de Riesgos y Emergencias (SNGRE)