During 15-22 May, IG reported that ash plumes intermittently visible from Tungurahua rose to altitudes of 5.1-7 km (16,700-23,000 ft) a.s.l. and drifted mainly W, NW, and E. Ashfall was reported from areas SW and W during 16-17 May, SW on 19 May, and W and NW during 20-21 May. Lahars and muddy waters traveled down W, NW, and N ravines during 15 and 17-19 May and caused the road to Baños to close on 18 May. Lahars that traveled in the Bilbao sector and down NW ravines on 20 May blocked the Baños-Penipe highway and obstructed the route between Ambato and Baños for about 6 hours. Muddy waters traveled down ravines to the N.

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)