During 27 August-2 September 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 roars and “gunfire” were heard that rattled structures at the observatory and around the volcano. On most days ash plumes rose 1.5-2.5 km (4,900-8,200 ft) a.s.l. above the crater rim and drifted N, W, and NW. On 27-28 August explosions expelled blocks on the W and NW flank that descended 800-1000 m below the crater rim. On 30 August pyroclastic flows decended 1500 m down the NW flank. IG reported nearly constant explosions and pyroclastic flows on 31 August that traversed down the ravines of La Hacienda, Achupashal, and Mandur.

On 1 September the explosions continued but were much smaller. Long-period earthquakes increased on 2 September, but explosions decreased with steam plumes containing little ash. On most days the Washington VAAC reported ongoing and continuous emissions, and ashfall was reported in several areas including Motilones, Chontapamba Pillate, Manzano, Chonglontus, Puela, Penipe, Quero, Cevallos Chontapamba, Bilbao, Cusúa, Pillate, La Calera, El Santuario, and El Rosario. . On 27 August the Washington VAAC reported that emissions rose to 6 km (22,000 ft) a.s.l. and on 30 August they rose to 6.7 km (20,000 ft) 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-EPN), Washington Volcanic Ash Advisory Center (VAAC)