During the report week, volcanic activity increased at Tungurahua. Eruptions began on 27 December at 1006 and 1427 that produced W-drifting gas-and-ash clouds to heights of 2 and 1 km above the volcano, respectively. A mudflow was reported on 29 December at 2342 travelling to the NW via Juive Grande Gorge. It affected the Pampa and Los Pájaros sectors. On 30 December at 0023 a seismic signal associated with an explosion was recorded, but the explosion was not observed due to cloudy conditions. Until 1500 ashfall was reported in the sectors of Guadalupe and Patate and may have also fallen to the W of the volcano. IG issued a SIGMET stating that at 0027 ash from the explosion rose to ~15 km. No ash was visible on satellite imagery.

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), Washington Volcanic Ash Advisory Center (VAAC)