IG reported that activity at Tungurahua remained at moderate-to-high levels during 17-22 September. On 18 September ash plumes rose 2 km and drifted mainly NW. Ashfall was reported in Cusúa (8 km NW), Mocha (25 km W), and Chacauco (NW), and windows vibrated at the Tungurahua Observatory (OVT) in Guadalupe (14 km N). An ash plume rose 2 km and drifted NW on 19 September. At night crater incandescence was noted and windows vibrated. A steam plume rose 2 km and drifted W and NW on 20 September, and ashfall was reported in Runtún (6 km NNE). On 21 September ash plumes rose 2.5 km and drifted NW; ashfall was reported in Manzano (8 km SW), Choglontus (13 km WSW), Bilbao (8 km W), Cusúa, Coltaló, and Motilones. Steam-and-ash plumes rose 2.5 km on 22 September and drifted W to NW. Ash fell in Cevallos, Quero, Mocha, and Tizaleo.

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)