No ash emissions from Tungurahua were reported by the IG between 27 September and 2 October. However, a slow-moving lava flow was seen moving down the NNW flank on 2 October. Some fumarolic activity from the crater was observed this week when the weather was clear. On 3 October an explosion sent an ash plume to a height of 5 km above the summit, about 10 km (6,200 ft) a.s.l. Ash fell in nearby communities to the W. Multiple sources that contributed to an aviation ash advisory that indicated a higher-level plume to 9.8 km (32,000 ft) a.s.l. extending E to a distance of 22 km.

Geological Summary. Tungurahua, a steep-sided andesitic-dacitic stratovolcano that towers more than 3 km above its northern base, is one of Ecuador's most active volcanoes. Three major edifices have been sequentially constructed since the mid-Pleistocene over a basement of metamorphic rocks. Tungurahua II was built within the past 14,000 years following the collapse of the initial edifice. Tungurahua II collapsed about 3,000 years ago and produced a large debris-avalanche deposit to the west. The modern glacier-capped stratovolcano (Tungurahua III) was constructed within the landslide scarp. Historical eruptions have all originated from the summit crater, accompanied by strong explosions and sometimes by pyroclastic flows and lava flows that reached populated areas at the volcano's base. Prior to a long-term eruption beginning in 1999 that caused the temporary evacuation of the city of Baños at the foot of the volcano, the last major eruption had occurred from 1916 to 1918, although minor activity continued until 1925.

Sources: Instituto Geofísico-Escuela Politécnica Nacional (IG-EPN), Washington Volcanic Ash Advisory Center (VAAC)