Based on information from the IG, the Washington VAAC reported that several small eruptions occurred at Tungurahua and that lahars were active in several sectors of the volcano. At 1600 on 25 April a pilot reported that ash was visible over the volcano at an altitude of ~7 km. Seismic activity indicated that brief eruptions occurred at 1230 on 28 April and at 1130 on 29 April, but extensive cloudiness prevented observations of the ash clouds. On 29 and 30 April lahars traveled to the Pampas, Cusuá, Hacienda, and Achupashal sectors and the river levels rose in the Ulba and Mandur sectors. The lahars in the Pampas sector blocked the Pelileo-Baños channel during 0710 to 1100 on 29 April and destroyed the highway. The IG warned that rainy conditions may cause more lahars and rising river levels near the volcano.

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)