IG reported that on 27 March, at 1716, an ash column from Tungurahua rose to an altitude of 11 km (36,000 ft) a.s.l. An accompanying pyroclastic flow traveled 1 km down the Mandur gorge on the NW flank. A lahar traveled W down the Bilbao gorge and vibrated near-by structures. On 28 March, ash plumes again rose to altitudes of 11 km (36,000 ft) a.s.l. Ashfall was reported from areas downwind. Noises that resembled rolling blocks down the flanks were reported. Hot steaming mudflows traveled N, NW, and W. On 29 March, three explosions rattled windows in areas as far away as 8 km. During 30 March-3 April, ash plumes, occasionally accompanied by roaring noises and "cannon shots," rose to altitudes of 6-10.5 km (19,700-34,400 ft) a.s.l. and drifted mainly W and NW. Incandescent material was ejected 300 m above the crater and subsequently descended about 1 m down the flank on 31 March; similar activity was observed at the summit during 1-2 April. Ashfall was reported from areas about 8 km SW, N, and W.

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)