IG reported that although cloud cover often prevented observations of Tungurahua during 1-7 May ash plumes were observed almost daily. Seismicity remained at a moderate level, although it increased on 4 May.

On 1 May an explosion and rolling blocks were heard, and ashfall was reported in El Manzano (8 km SW). The next day steam-and-ash plumes rose 1-1.5 km above the crater and drifted W. Ashfall was reported in Cevallos (23 km NW), Tisaleo (29 km NW), Quero (20 km NW), and Mocha (25 km WNW). During 2-4 May Strombolian activity was observed at night. On 3 May several explosions produced ash plumes that rose 2-3 km above the crater and drifted N and NW. Ash fell in Juive (7 km NNW), Runtún (6 km NNE), Pondoa 8 km N), Baños (8 km N), Patate (NW), Pelileo (8 km N), Ambato (31 km NW), Cevallos, and at the Tungurahua Observatory (OVT) in Guadalupe (14 km N). On 4 May explosions rattled windows in Baños, and ash plumes rose 1-1.5 km and drifted N and NW. Large lahars traveled down the La Pampa drainage on the S flank, while other lahars traveled down the Vazcún, Juive, and Mandur drainages on the N and NW flanks. Explosions on 5 May rattled windows in Ventanas, Pondoa, and Runtún. An ash plume rose 2 km and drifted W. Ashfall was again reported in Cevallos, Tisaleo, Quero, and Mocha. A pyroclastic flow descended the NW flank 2 km. On 6 May ash plumes drifted SW and ashfall was reported in Cevallos, Tisaleo, Quero, Mocha, Pillate (8 km W), Choglontus (SW), and El Manzano. The next day ash plumes rose 3 km and drifted SW. Ashfall was reported in Sabañag (15 km WNW), Chazo, Ilapo, and Riobamba (30 km S).

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)