IG reported that seismic activity at Tungurahua was at low levels during 10-11 July, increased to moderate levels on 12 July, and increased again to moderate-to-high levels on 13 July; the number and type of events gradually and constantly increased. Cloud cover prevented visual observations of the crater. A total of 266 long-period events were recorded from 1500 on 13 July through the time of a large explosion at 0647 on 14 July, which was heard in areas as far as Guayaquil (about 180 km SW).

At 0651 an ash plume generated by the explosion rose 5.1 km above the crater and several significant pyroclastic flows descended the Achupashal ravine (NW). Continuous tremor was detected until 0840, and then seismicity dramatically decreased. At 0842 the plume rose to 8.3 km above the crater and drifted N, W, and S. At 0930 the plume drifted N and was observed drifting over the E parts of Quito (130 km N). Heavy amounts of ash and tephra fell in areas near the volcano including Bilbao (W, 4 cm diameter), Chacauco (NW, 5 cm diameter), Cotaló (8 km NW), Cahuají (8 km SW), Choglontus (SW), El Manzano (8 km SW), Puela (8 km SW), and Penipe (15 km SW); thinner deposits were reported in towns including Pelileo (8 km N), Ambato (31 km N), Cevallos (23 km NW), Colta (45 km SW), Guanujo (65 km WSW), and Guaranda (65 km WSW), and in the cantons of Guano (30 km SW), Valencia, Empalme, Buena Fé, and areas in the province of Manabi (180 km NW). According to news articles, over 200 people were evacuated from Cusua, Chacauco, and Juive.

On 15 July steam plumes were observed rising from the crater during times of better visibility. Long-period earthquakes and tremor were detected during 15-16 July. Ashfall was reported in El Manzano on 16 July; cloud cover continued to prevent observations of the crater.

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), Associated Press