IG reported that during 2-12 March seismicity and sulfur dioxide emissions at Tungurahua were both moderate to high. Over 100 earthquakes were detected daily; 157 high-frequency tremors were recorded on 3 March and 233 long-period events were recorded on 6 March. Deformation measurements indicated that the rising magma body was small and concentrated beneath the NW flank.

Although cloud cover often prevented visual observations during 6-12 March, ash emissions were observed almost daily. On 6 March a steam plume with low ash content rose 1.5 km above the crater. Roaring was heard at night during 6-7 March, and ashfall was reported in Palitahua (S), El Manzano (8 km SW), Penipe (15 km SW), and Choglountus (SW). Ash plumes rose 1 km above the crater on 7 March and 2 km the next day, drifting W. During 8-12 March Strombolian activity ejected incandescent blocks that rolled at most 500 m down the flanks. Ash plumes drifted S, SW, and W. Ashfall during 10-11 March was reported in El Manzano and Choglountus. On 11 March ashfall was also reported in Pillate (8 km W).

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)