IG reported that during 25-31 July visual observations of Tungurahua were limited due to cloud cover. On 25 July incandescence from the crater was observed at night, an explosion generated a "cannon shot" noise, and there were sounds resembling blocks rolling down the flanks. The next day a steam plume rose 200 m above the crater and drifted W. The Juive (NNW), La Pampa (S), and Mapayacu (SW) drainages contained muddy waters on 29 July; water on the Mapayacu drainage carried blocks that were 50 cm in diameter. An explosion on 30 July produced sounds resembling rolling blocks and caused vibrating windows in surrounding areas. One small explosion was detected on 31 July.

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-EPN)