The IG reported that although visual observations were occasionally limited due to cloud cover during 29 April-6 May, ash-and-steam plumes from Tungurahua were spotted and generally rose to altitudes of 5.5-7 km (18,000-23,000 ft) a.s.l. Ashfall was reported in areas to the SW and W during 29 April-1 May and on 4 May. On 30 April, explosions produced steam-and-ash plumes to altitudes of 9-10 km (29,500-32,800 ft) a.s.l. Incandescence at the summit was visible and incandescent blocks rolled down the flanks. Roaring noises were audible. On 1 May, explosions were accompanied by "cannon shots" and intense incandescence at the summit. Windows vibrated in areas 6 km NE. Incandescent blocks rolled 1 km down the flanks. On 3 May, a small lahar descended the W flank.

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)