Report on Tungurahua (Ecuador) — 18 May-24 May 2011
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 18 May-24 May 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, 18 May-24 May 2011. Smithsonian Institution and US Geological Survey.
1.467°S, 78.442°W; summit elev. 5023 m
All times are local (unless otherwise noted)
IG reported that on 17 May new fumaroles on Tungurahua's W flank, about 1 km below the crater, were observed from the Tungurahua Observatory (OVT) in Guadalupe (11 km N). Explosions during 17-23 May produced gas-and-steam plumes that rose to altitudes of 6-9 km (19,700-29,500 ft) a.s.l and mostly drifted SW, W, and NW. Ashfall was reported on most days in areas within 8 km SW, W, NW, N, and NNE, but reached as far as Guadalupe (11 km N), Ambato (31 km NW), and Penipe (15 km SW). On 17 May incandescence emanated from the crater. Blocks were also ejected from the crater, and rolled down the flanks, on 17, 19, and 21 May. Sounds resembling "cannon shots" were occasionally reported. Large windows vibrated on 21 May. Ash-and-gas plumes rose from the crater on 24 May and likely drifted W.
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.