A large eruption of Tungurahua began on 16 August at 1900 and continued to 17 August at 0200, when activity began to diminish. According to the Instituto Geofísico, seismic activity increased on 16 August and clinometer measurements indicated a bulge on the N flank as compared to 11 August measurements. Ash-and-gas plumes reached heights of 3 km above the summit (26,300 ft a.s.l.) and drifted W and NW. About 3,200 people were evacuated from at-risk areas. On 17 August, about 20 pyroclastic flows traveled NW through the Achupashal, La Hacienda, and Mandur drainages, and NNW towards the Juive and Vazcún drainages. The Chambo and Puela rivers and several roads to the W and S were blocked by pyroclastic-flow debris. Tephra fall (3 cm in diameter) was reported from several areas in a zone that extended from Penipe in the SW to about 15 km NW. Ash plumes reached estimated heights of 10 km above the summit (49,000 ft a.s.l.) and covered the central part of Ecuador, forming a cloud ~742 km long and ~185 km wide trending NNW and SSE.

On 18 August, incandescent blocks were ejected from the summit and descended about 1.7 km down the flanks. Based on seismic interpretation, one of the blockages damming part of the Chambo River had been breached. During 18-19 August, the N flank continued to inflate. During 20-21 August, steam emissions were observed during breaks in the cloud cover and the N flank exhibited deflation. On 23 August, two lava flows were identified on the NW slope moving at a slow rate.

According to news reports, ash and debris fall caused fires and severe damage to five villages. An estimated 20,000 hectares (50,000 acres) of crops were destroyed. At least five people are dead or missing, and several more were injured. An estimated 4,000 people have been relocated to shelters.

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.

Sources: Agence France-Presse (AFP), Associated Press, ReliefWeb, Instituto Geofísico-Escuela Politécnica Nacional (IG-EPN), ReliefWeb