IG reported that seismicity decreased after a period of Strombolian activity at Tungurahua detected during 1900-2100 on 11 October; explosions were detected at 2015, 2110, and 2248. An explosion at 2318 on 13 October ejected blocks onto the W flank. Ashfall was reported in Choglontus (13 km WSW) the next morning. Cloud cover often prevented views of the summit area during 14-20 October. Ash fell in Cotaló (8 km NW), Bilbao (8 km W), and Choglontus on 19 October. Later that day a steam-and-ash emission rose 500 m above the crater and drifted W. Ashfall was reported in Manzanó (8 km SW) on 20 October.

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.

Source: Instituto Geofísico-Escuela Politécnica Nacional (IG-EPN)