Report on Tungurahua (Ecuador) — 29 February-6 March 2012
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 29 February-6 March 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, 29 February-6 March 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 during 29 February-2 March cloud cover prevented views of Tungurahua. On 3 March seismicity increased. Clouds mostly prevented observations; during breaks in the cloud cover ash plumes were observed rising 3 km above the crater and drifting S and SW. Explosions ejected blocks that rolled down the flanks. Two of the explosions generated sounds resembling cannon shots, and vibrated windows. Ashfall was reported in Choglontus (13 km WSW), Manzano (8 km SW), Cahuají (8 km SW), and Motilones (W). On 4 March ashfall was reported in Yuibug and observers noted hot deposits from a small pyroclastic flow that occurred high in the Achupashal drainage (NW). Ash plumes observed during breaks in the cloud cover on 5 March rose 1 km and drifted W. Ash again fell in Choglontus. Clouds prevented observations on 6 March.
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.