Report on Tungurahua (Ecuador) — 21 December-27 December 2011
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 21 December-27 December 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, 21 December-27 December 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 increased seismicity from Tungurahua was detected during 21-27 December. On 22 December ash plumes rose 500 m above the crater and drifted 2 km W. Ashfall was reported in Baños, Vazcún, and Manzano. One explosion at 0850 generated two small pyroclastic flows that descended the Achupashal and Hacienda drainages. Gas-and-ash plumes rose 4 km a.s.l. and drifted NE. On 23 December ash and gas emissions continued and at night Strombolian activity was observed with blocks rising 500 m above the crater. Ashfall was reported in Cahuají, Manzano, and Choglontus. On 24 December roaring noises were heard and ashfall in Cahuají, Manzano, and Choglontus was reported. An ash plume rose 500 m above the crater and drifted W and SW with ashfall reported in Manzano.
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.