Report on Tungurahua (Ecuador) — 22 August-28 August 2012
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 22 August-28 August 2012
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2012. Report on Tungurahua (Ecuador). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 22 August-28 August 2012. 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 at about noon on 21 August Tungurahua entered a second stage of activity since the onset of the eruption that began early in August. The second stage was characterized by low-to-moderate levels of activity; emissions decreased and intense seismic tremor declined to sporadic episodes lasting only a few minutes. During 22-28 August visual observations were often limited due to cloud cover. On 22 August steam-and-gas plumes rose from the crater, roaring was heard, and ashfall was reported in Choglontús (SW). Explosions at night ejected incandescent tephra that landed on the flanks 500 m below the crater. The next day gas-and-ash plumes rose 1.5-4 km above the crater and drifted W and NW. Ashfall was reported in Choglontús, Pillate (7 km W), and El Tablón. On 24 August gas-and-ash plumes rose 2 km and drifted W. During 24-25 August ash fell in Manzano (8 km SW), Choglontus, Chacauco (NW), Bilbao (8 km W), and Pillate. Explosions on 26 August generated ash-and-gas plumes that rose 2-3 km and drifted NW.
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.