During 19-25 July, visual observations of Tungurahua were limited due to heavy cloud cover. Based on seismic interpretations, daily explosions recorded during the week were mostly small to moderate in intensity. Small pyroclastic flows descended NW a maximum distance of 1 km on 21 and 23 July. Steam-and-ash plumes were observed during 19-22 and 24 July and reached maximum heights of 5 km above the summit (32,900 ft a.s.l.) on 21 July. According to the Washington VAAC, pilots reported on 19, 22, and 23 July that ash plumes reached altitudes of 10.7 km (35,000 ft) a.s.l. and drifted predominantly W. A hot spot was visible on satellite imagery from 19 to 22 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.

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