Report on Tungurahua (Ecuador) — 20 April-26 April 2011
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 20 April-26 April 2011
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2011. Report on Tungurahua (Ecuador). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 20 April-26 April 2011. Smithsonian Institution and US Geological Survey.
1.467°S, 78.442°W; summit elev. 5023 m
All times are local (unless otherwise noted)
On 22 April, IG reported that in recent months the seismic network at Tungurahua detected volcano-tectonic earthquakes, indicating increased pressure in the volcano. Deformation of the NW quadrant that began in early February was slow but continuous, and then accelerated during the previous nine days. On 21 April gas-and-ash plumes caused fine ashfall in Choglontús and Cahuají (8 km SW), Pillate (8 km W), Cotaló (8 km NW), Juive (7 km NNW), and Baños (8 km N). Strombolian activity was seen at night, producing small lava fountains and incandescent blocks that rolled 1 km down the flanks. Roaring was heard and a few explosions occurred during 21-22 April. IG recommended that residents do not go within 3 km of Tungurahua's crater. On 26 April six explosions were detected and constantly-generated ash plumes rose to an altitude of 12 km (39,400 ft) a.s.l. Plumes drifted W and NW, causing steady ashfall in areas downwind. Structures vibrated in surrounding areas, including in Baños.
Geologic Background. 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 itself collapsed about 3000 years ago and produced a large debris-avalanche deposit and a horseshoe-shaped caldera open to the west, inside which the modern glacier-capped stratovolcano (Tungurahua III) was constructed. 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.