IG reported a high level of activity at Sangay during 23-30 May, though weather clouds sometimes prevented visual observations. There were 304-600 daily explosions recorded by the seismic network; no data was reported on 28 May. Ash plumes were seen in webcam images and reported by the Washington VAAC almost daily. On 23 May incandescent material extending 1.8 km down the SE flank was visible in webcam images. On 24 May pyroclastic flows descending 200 m were visible in between somewhat-dense weather clouds. An ash plume rose 300 m and drifted W. On 25 May ash plumes rose as high as 2 km and drifted NE and SE. Ash emissions were visible in webcam images at 1734 and were continuous for a period of time. Crater incandescence was visible overnight during 25-27 May and ash plumes that rose 500-800 m drifted SW and NW during 26-27 May. Incandescence from the lava flow on the SE flank was noted overnight during 28-29 May. The VAAC reported that at 0610 on 29 May ash plumes were visible in satellite images drifting W at 30,000 ft a.s.l., or 3.9 km above the summit, and drifting N at 40,000 ft a.s.l., or 6.9 km above the summit. Several pyroclastic flows descending the SE flank were visible in webcam images at 0615. At 1730 ashfall was reported in Cebadas Parish (Chimborazo province). 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)