Although storm clouds occasionally prevented observations of Tungurahua's summit area, steam-and-gas plumes were seen on 22 and 23 June and steam-and-ash plumes were seen during 24-28 June. The plumes rose as high as 1 km above the crater and drifted NW, W, and SW. During most days ash fell in areas within 8 km SW and occasionally in areas 8 km W and NW. Roaring noises were sometimes heard, and on 25 June were followed by vibrating windows 8 km W and SW. Lahars on 26 June traveled down drainages to the NW and W carrying blocks up to 2 m in diameter. On 27 June ashfall was reported from areas 23 km NW and 25 km W. During 27-28 June incandescence emanated from the crater at night.

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)