The IG reported that although visual observations were limited due to cloud cover, ash and ash-and-steam plumes from Tungurahua were spotted and rose to altitudes of 5.5-9 km (18,000-30,000 ft) a.s.l. during 2-8 April. Ash plumes drifted in almost all directions; ashfall was reported in areas downwind during 4-8 April. Explosions were occasionally registered by the seismic network and roaring and "cannon shot" noises were reported. Incandescent material rolled 0.5-1 km down the flanks during 2-4 and 6-7 April and Strombolian activity at the summit was noted during 3-4 April.

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)