Although storm clouds occasionally prevented observations of Tungurahua's summit area during 16-18 June, steam-and-ash plumes were seen that rose to altitudes of 5.5-7 km (18,000-23,000 ft) a.s.l. Daily reports of ashfall came from multiple areas about 8 km W and SW, but ash was noted as far away as 15 km SW on 17 June. Ashfall in Cahuají (8 km SW) covered pastureland, preventing animals from grazing. Roaring noises were occasionally reported. During 17-18 June, incandescence from the crater was seen at night. An explosion was followed by roaring noises, sounds resembling blocks rolling down the flanks, and incandescence.

On 19 June steam-and-ash plumes rose 500 m above the crater and large windows vibrated after noises were heard. The next day snow covered parts of the E and S flanks. Steam-and-gas plumes rose 500 m and drifted SSW, E, and NW during 20-21 June. Lahars in drainages to the SW carried blocks up to 50 cm in diameter. On 21 June ashfall was reported in areas 8 km W.

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)