IG reported moderate seismic activity at Tungurahua during 14-21 July, characterized by long-period events, tremor, and a few explosions. Cloud cover often prevented visual observations. Explosions during 14-15 July generated ash plumes that rose 2 km above the crater and drifted W. Crater incandescence was visible at night. Ashfall overnight during 15-16 July was reported in Choglontus (13 km WSW), Bilbao, and El Manzano (8 km SW). On 17 July vapor-and-ash plumes were observed and ash fell in Choglontus. A lahar descended the Juive (NW) drainage on 18 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)