IG reported that during the morning of 30 January the seismic network recorded an increase in the number of events at Tungurahua including some low-magnitude explosions, long-period events, and seismic tremor. Ashfall was reported in Pungal (40 km SSW), Penipe (15 km SW), and Palictahua in the district of Penipe. Cloud cover prevented ground observations, but IG noted that satellite images indicated the presence of ash plumes and thermal anomalies. The number and size of explosions increased at night during 30-31 January, and then a sharp decline in activity was noted on 31 January, characterized by very low seismicity. At 1701 an explosion generated an ash plume that rose 2 km and drifted SE and SW.

On 1 February, between 0800 and 1700, a swarm of volcano-tectonic earthquakes occurred in the upper conduit. Two moderately-sized explosions, at 1712 and 1732, generated ash plumes that rose 5 km, and pyroclastic flows that traveled 500 m down the NE and NW flanks. A larger explosion at 1739 produced an ash plume that rose 8 km and drifted SE and possibly SSE. Based on reports from IG, satellite images, pilot observations, web-camera images, and the Guayaquil MWO, the Washington VAAC reported that the ash plume rose to an estimated altitude of 13.7 km (45,000 ft) a.s.l., and drifted S at high altitudes and SW at lower altitudes. IG noted that pyroclastic flows traveled 7-8 km, reaching the base of the volcano and traveling over the Achupashal Baños- Penipe highway. Continuous ash-and-gas emissions followed; ash fell in multiple areas and total darkness was reported in Chacauco (NW). Explosions occurred every minute and vibrated structures in local towns. Pyroclastic flows descended the SW, W, NW, and NE flanks, and stopped short of towns and infrastructure. Ash emissions were sustained through the rest of the evening, and Strombolian explosions ejected incandescent blocks 800 m above the crater that fell and rolled 500 m down the flanks.

Activity gradually declined at 1900 until 2100 when explosions became more sporadic. On 2 February explosions at 0659, 0723, and 0801 were followed by ash emissions. During 2-3 February at least 10 explosions occurred and were heard in areas several kilometers away. On 3 February an ash plume rose 4 km and drifted N, reaching Quito as a mist of suspended very fine material that lingered most of the day.

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-EPN), Washington Volcanic Ash Advisory Center (VAAC), Prensa Latina