The IG reported that although visual observations were occasionally limited due to cloud cover during 22-28 April, ash-and-steam plumes from Tungurahua were spotted and rose to altitudes of 6-8 km (19,700-26,200 ft) a.s.l. Ashfall was reported in areas downwind on 23, 25, and 28 April. On 22 April, a small lahar descended the Mapayacu drainage to the SW. On 23 April, explosions accompanied by "cannon shot" noises produced ash plumes that drifted WSW and caused windows to rattle in areas to the NW, W, and SW. Blocks rolled 600 m down the flanks. On 25 April, fumarolic activity was noted on the interior of the NE crater rim. Sounds resembling blocks rolling down the flanks were reported.

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)