IG reported moderate-to-high seismic activity at Tungurahua during 22-28 April, characterized by long-period events, tremor, and explosions. Cloud cover often prevented visual observations, and rainfall was recorded almost daily. During 22-23 April gray and red ash fell in Choglontus (13 km WSW), and a landslide in the area of Manto de la Novia was reported in the morning. During 23-24 April gray tephra fell in Bilbao (W), Chontapamba (W), Pillate (8 km W), Baños (8 km N), and Quero (20 km NW). Emissions with minor ash content were visible on 24 April; one emission rose 200 m and drifted NW. Ashfall on 25 April was reported in Chontapamba, Pillate, Romero, and Guambaló. During 25-26 April lahars descended the Quero, Bilbao, Chontapamba, Juive (NW), Mapayacu (SW), Pingullo (NW), Pondoa (N), Vazcún (N), Achupashal (NW), La Pirámide (NW), and Romero drainages. On 27 April ash fell in Pillate, and a vapor emission rose 2 km and drifted W. On 28 April an emission with a minor ash content rose 3 km and drifted W. Roaring was noted and lahars descended the La Pampa (NW) and Rea drainages.

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)