Volcanic and seismic activity were at relatively low levels at Tungurahua during 23-28 February. Low-energy gas, steam, and ash plumes were emitted. In addition, long-period earthquakes and episodes of tremor were recorded. During the report period ashfall was reported in towns near the volcano, including Puela (SW of the volcano), San Juan de Pillate, Cusua, and Quero. On 23 February the daily sulfur-dioxide flux was 1,200 tons. On 27 and 28 February, rains generated lahars in the W zone of the volcano into the gorges of Cusua and Bilbao.

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)