IG reported that although visual observations were occasionally limited due to cloud cover, ash-and-steam and ash plumes from Tungurahua were seen and rose to altitudes of 6-8 km (19,700-26,200 ft) a.s.l. during 25 December-1 January. Plumes drifted predominantly W and ashfall was reported in areas downwind and to the SW and N. Roaring noises and "cannon shots" were heard almost daily and windows and floors vibrated on 26, 27, and 30 December. During 26-27 December, incandescent blocks rolled down the flanks as far as 500 m. On 29 December, incandescent material observed at the summit was associated with explosive events. Incandescent blocks rolled 700 m down the NW flank on 29 December and 1,200 m down the flanks on 30 December. Incandescence at the summit was noted again on 31 December during the night.

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)