During the week several small eruptions occurred at Tungurahua and seismic activity was at high levels. Based on information from the IG, the Washington VAAC reported that an ash emission at 1608 on 13 March produced an ash cloud that rose to ~9.6 km a.s.l. and drifted to the NW. The IG stated that the transmission lasted ~10 minutes and that light ash fell in the towns of Cotalo and Pillaro. At 1415 on 15 March an eruption produced an ash cloud that rose ~3.2 km above the volcano. An ash emission occurred at 1756 on 16 March that rose to 8.8 km a.s.l. and drifted to the ENE.

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)