IG reported that activity at Tungurahua remained high during 23-27 October. Although cloud cover sometimes prevented visual observations of the crater, ash plumes were observed almost daily. During 23-24 October continuous ash emissions produced plumes that rose 3-4 km above the crater and drifted NNE and SW. Ashfall was reported in Penipe (15 km SW), Palitahua (S), Riobamba (30 km S), Tisaleo (29 km NW), El Manzano (8 km SW), and Choglontus (SW). On 25 October blocks were observed rolling down the flanks, and ash fell in El Manzano and Choglontus. The next day continuous ash emissions rose 2 km and drifted SW. Ashfall was noted in Cevallos (23 km NW), Mocha (25 km WNW), Tisaleo, Penipe, El Manzano, and Cloglontus. Ash plumes rose 2 km and drifted W on 27 October. Low-energy gas-and-ash emissions drifted W and SW on 28 October. Ashfall was reported in Palitahua. On 29 October ash plumes rose 4 km and drifted E and NE. Ash fell in Penipe, Mocha, and El Manzano.

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)