During 20-26 August IG reported that moderate to high eruptive activity continued at Tungurahua, including volcanic tremor, explosions, and long-period earthquakes. On most days explosions described as “canon like” blasts, roars, and “gunfire” were heard near the volcano and rattled windows in the town of Baños on 21 August. On most days ash plumes rose 1.5-5 km (4,900-16,400 ft) above the crater rim and drifted W and SW. On 22-23 August views through intermittent clouds showed blocks falling on the E flank of the volcano and on 24-25 August incandescent blocks fell 1-1.5 km below the crater rim. On 23-26 ashfall was reported in several areas, including Bilbao, Chacauco, Mocha, Choglontus, Tisaleo, and El Manzano. On 26 August muddy water was observed after rains in Mapayacu Gorge. On most days the Washington VAAC reported ongoing and continuous emissions. On 21 August the Washington VAAC reported emissions rose to 6 km (20,000 ft) a.s.l. and on 24 August emissions rose to 8.5 km (28,000 ft) a.s.l. On 26 August short duration explosions were reported.

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)