IG reported a high level of activity at Sangay during 10-16 March. Seismicity was characterized by daily explosions, long-period earthquakes, and signals indicating emissions. Weather clouds often prevented visual observations of the volcano, but satellite and webcam images recorded daily ash plumes.

Ash plumes were notable during 10-11 March and impacted communities downwind with ashfall. Pyroclastic flows, visible in webcam images, descended the flanks at 0950 on 10 March. The Washington VAAC stated that ash plumes rose 6.7-8.5 km (22,000-28,000 ft) a.s.l. and drifted W at lower altitudes and NW at higher altitudes. A period of explosions recorded during 0315-0545 on 11 March produced ash plumes that rose as high as 13.7 km (45,000 ft) a.s.l., or 8.5 km above the summit, and drifted NW, W, and SW. Ash plumes drifted N, NW, and W, causing significant ashfall in Guamote (42 km WNW), notable ashfall in Chambo (43 km NW), Riobamba (50 km NW), Penipe (55 km NW), and Guano (55 km NW), and minor ashfall in Colta (55 km NW), Alausí (60 km SW), and Macas. According to a social media video post the ash plumes caused widespread darkness in Riobamba for several hours. Other residents posted photos of crops covered in ash. The eruption released 31 kilotons of sulfur dioxide, the highest value recorded during the current eruptive period that began in May 2019.

Heavy rainfall overnight during 11-12 March caused hot lahars in the Volcán River drainage that reached the confluence of the Upano River. Overflows in the Upano River resulting in additional lahars and debris flows. Weather clouds hindered visual observations. During 13-15 March gas-and-ash plumes rose as high has 2 km above the summit and drifted NE. Seismic signals indicating lahars were recorded on 14 March. The VAAC reported that ash plumes rose to 6-9 km (20,000-30,000 ft) a.s.l. and drifted W and WNW on 16 March.

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), Darwin Volcanic Ash Advisory Centre (VAAC), Marlon Puertas