On 29 May, IG reported that activity from Tungurahua had gradually increased during the previous few weeks. On 23 May, a marked increase in the number of explosions and the intensity and frequency of ash plumes and ashfall was noted. Although visual observations were mostly limited due to cloud cover during 28 May-2 June, steam and ash-and-steam plumes were spotted and rose to altitudes of 6-7 km (19,700-23,000 ft) a.s.l. Ashfall was reported in areas downwind. On 29 May, seismicity increased; several episodes of seismic tremor were detected. Two episodes were accompanied by roaring noises, ash emissions, and incandescent blocks that were ejected from the summit and rolled down the flanks. A thermal anomaly was detected in satellite imagery. Pyroclastic flows descended the N and NW flanks; deposits were observed the next day. On 30 May, emissions of plumes with low ash content were constant and roaring noises were reported. Slight roaring noises were reported on 1 and 3 June.

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)