Volcanic activity increased at Tungurahua. A large number of long-period earthquakes accompanied several small eruptions and near-continuous gas-and-ash emission. The IG reported that an eruption on 31 May at 2120 produced an ash cloud that rose up to ~7.9 km a.s.l. and drifted to the W. Incandescent blocks were ejected during the eruption, and an acoustic wave that sounded like a cannon shot was heard several km away from the volcano. Eruptions also occurred on 29 May at 2012 that sent ash to a height of ~8.2 km a.s.l., on 30 May at 1211 (ash plume to an unknown height), and on 2 June at 1709 with an ash plume to ~7.9 km. Incandescent material was visible in the crater, and IG warned that heavy rain could remobilize ash and generate lahars.

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.

Sources: Washington Volcanic Ash Advisory Center (VAAC), Instituto Geofísico-Escuela Politécnica Nacional (IG)