IG reported that during 19-25 activity at Tungurahua remained high. On 19 December there were 60 explosions detected by the seismic network; explosions vibrated structures and were often heard by local residents. Ash plumes rose 2 km above the crater and drifted SW, causing ashfall in communities downwind including Choglontús (SW), Manzano (8 km SW), Palitahua (S), and Puela (8 km SW). The next day 78 explosions were detected, roaring was heard, and windows vibrated. Ash plumes rose 1 km and drifted W and SW. Ashfall was reported in Manzano, Palitahua, Choglontús. A pyroclastic flow, generated after an explosion, traveled 2 km down drainages on the NW flank.

During 21-25 December explosions ejected incandescent blocks that rolled as far as 1 km down the flanks. Gas-and-ash plumes rose less than 2 km above the crater and drifted W and NW. On 22 December ashfall was reported in Pillate and Manzano, and lava fountains 500 m high were observed at night. On 23 December explosions rattled windows. Strombolian explosions ejected incandescent blocks more than 500 m above the crater that rolled 1 km down the W and NW flanks. The next day seismicity decreased and minor ashfall Choglontús in was reported.

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)