The Instituto Geofísico-Escuela Politécnica Nacional (IG-EPN) reported high levels of eruptive activity at Sangay during 21-29 April. The seismic network recorded 124-258 daily explosions. Several ash-and-gas plumes were observed rising more than 4 km above the summit during 22-24 April, as high as 3 km above the summit during 24-25 April, and up to 1.7 km above the summit during the rest of the week; weather clouds sometimes obscured views during the last half of the week and almost completely obscured views during 21-22 and 26-27 April. The ash-and-gas plumes drifted mainly NW, W, and SW. Minor ashfall was reported in the province of Chimborazo during 22-25 April, and especially in the parish of Cebadas and in Utucun, Rayoloma, and Pueblo Cebadeño during 23-24 April. Nighttime crater incandescence was visible. On most nights several incandescent avalanches were observed descending the SE flank as far as 1 km below the summit. Incandescent material was ejected 100 m above the summit during 23-24 April. Secretaría de Gestión de Riesgos (SGR) maintained the Alert Level at Yellow (the second highest 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), Secretaría de Gestión de Riesgos (SGR)