IG reported that a swarm of volcano-tectonic and long-period earthquakes began at Tungurahua at 1105 on 26 February. At 1211 an explosion produced a plume with high ash content that rose 5 km above the crater and drifted W. Ash fell in Juive (NW), Chico, Choglontús (13 km WSW), El Manzano (8 km SW), and Cahuají (8 km SW). Explosions at 1239, 1247, and 1252 generated ash plumes that rose 6-7 km above the crater. An explosion at 1333 generated a small pyroclastic flow that descended halfway down the W and NW flanks, and an ash plume that rose 8 km. At 1535 another pyroclastic flow, generated from material spilling over the WNW rim, also traveled halfway down the volcano in the Mandur (NW), Hacienda (NW), and Cusua (NW) drainages. Ashfall was noted in El Manzano, Choglontús, Pillate (8 km W), Juive, Ambato (31 km NW), and Quero (20 km NW); reddish, black, gray, and beige tephra up to 3 mm in diameter fell in Pillate and Choglontús. In the evening Strombolian activity ejected incandescent blocks which rolled 1.5 km down the flanks. For a short time around 2200 lava fountains rose 500 m.

Explosions and nighttime crater incandescence continued to be detected during 27 February-1 March, and explosions sometimes vibrated nearby structures. Ashfall was observed daily in areas including El Manzano, Palitahua (6 km SSW), Cotaló (8 km NW), Cahuají, Providencia, Puela (8 km SW), Chazo, Pillate, Choglontús, Mocha (25 km WNW), and areas of Quero. Ash plumes were observed rising 2-4 km above the crater on 27 February and 1 March. During 29 February-1 March pyroclastic flows descended the Juive, Mandur (NW), Achupashal (NW), and Romero drainages; the largest traveled 1.5 km down the Achupashal.

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)