IG reported that ash plumes from Tungurahua, occasionally noted after explosions, rose to altitudes of 5.5-9 km (18,000-29,500 ft) a.s.l. during 17-23 October. Plumes drifted all directions, except to the E and SE. On 17 October, incandescent material propelled from the summit by explosions fell onto the flanks. A resultant ash plume drifted W. Fumarolic activity was noted on the NW flank. During 17-18 October, ashfall was reported from areas to the NW, N, and SW. On 19 October, lahars descended NW drainages and consequently the road between Ambato and Baños was closed.

During 20-21 October, explosions vibrated windows and doors in areas 8 km to the SW and N, including Tungurahua Observatory (OVT) in Guadalupe, 11 km N. On 21 October, incandescent material was ejected from the crater and roaring noises were heard. Ashfall was reported from areas to the SW on 21 October.

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)