Observations of Tungurahua's summit area during 21-27 July were sometimes not possible due to inclement weather. Ash plumes seen during 21-23 July rose to altitudes of 6-9 km (19,700-29,500 ft) a.s.l. and drifted W and NW. Ashfall was reported in areas within 10 km NW, W, and SW during 22-24 July. Steam plumes were seen rising 200 m above the crater on 25 July and an explosion was heard on 26 July. On 27 July a series of explosions was detected by the seismic network. Roaring noises were followed by vibrating windows in areas to the N and NW. Slight ashfall was noted in areas to the SW and W, and as far as 23 km NW.

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)