IG reported that the eruption at Sangay that began on 7 May was continuing as of 4 December without a notable increase or decrease in activity levels. Activity was concentrated at two eruptive centers: the Central Crater and the Ñuñurcu dome (located 190 m SSE of Central Crater). Sporadic explosions at Central Crater produced ash plumes that rose as high as 2 km above the crater rim and drifted mainly NE during the previous month. Minor ashfall was recorded in the towns of Alao (20 km NW), Cebadas (35 km WNW), and Guaguallá (Chimborazo province), in Macas (42 km SSE, Morona-Santiago province), and in the Azuay province. Almost continuous lava effusion from the Ñuñurcu dome fed lava flows that traveled down the SE flank.

Collapses along the margins of the lava flows generated small pyroclastic flows and small rockfalls that reached the upper channel of the Río Volcán. These deposits created dams which were remobilized by rainfall into lahars, which in turn partially dammed parts of the river at the confluence of the Río Upano. Parque Nacional Sangay and IG-EPN staff measured deposits at the confluence that were more than 2 m thick on 27 November; similar deposits were observed along a 16-km stretch upsteam. Sulfur dioxide emissions up to 640 tons/day were detected by satellite in recent weeks, and a strong sulfur odor was noted around 1 km above the crater rim during a 3 December overflight.

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)