According to reports from IG, about one small explosion per day has occurred at Tungurahua since the explosion on 17 June produced an ash cloud that rose to 7 km above the summit. The explosions have usually occurred with no warning, and light ash fall has frequently fallen to the W of the volcano, often damaging crops. The Washington VAAC reported that during the week the IG stated that seismic activity on 28 June at 1824 suggested that an eruption may have produced an ash cloud that rose to 7 km a.s.l. The ash cloud was not visible in satellite imagery. On 3 July at 0715 the Washington VAAC issued a report that a pilot observed W-drifting ash over the volcano between 5.8 and 7.6 km a.s.l.

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