Report on Tungurahua (Ecuador) — 23 November-29 November 2011
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 23 November-29 November 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, 23 November-29 November 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 at 1540 on 27 November, and at 1650 the seismic network recorded four volcano-tectonic earthquakes. Two small explosions at 1701 and 1705 were followed by a large explosion at 1718. Pyroclastic flows descended the Achupashal, Chotanpamba, and Mandur drainages on the NW and W flanks. Two more large explosions were detected at 1731 and 1735. Incandescent blocks traveled 1 km down the flanks, and roaring noises and sounds resembling "cannon shots" were reported. Ashfall was reported in Manzano (8 km SW), Bilbao (8 km W), and Pillate (8 km W), ash and tephra fell in Cotaló (8 km NW), and tephra fell in Cusúa (8 km NW). At 1905 a pyroclastic flow descended the S and SW flanks.
At 0200 on 28 November an explosion ejected incandescent material that fell on all flanks, and generated a pyroclastic flow that descended the Achupashal drainage. Starting before 0500 until 0900 an almost constant roar was heard and incandescent blocks traveled 1 km down the flanks, especially towards the W and NW. Three pyroclastic flows were noted on the S flank. Windows vibrated at the Tungurahua Observatory (OVT) in Guadalupe (14 km N). During the day, an ash plume rose 3 km above the crater and drifted in multiple directions. White ashfall was reported in Manzano, Choglontús (SW), Pondoa (8 km N), and Runtún (6 km NNE). In the evening incandescent blocks that were ejected 300 m above the crater rolled 400-500 m down the flanks. On 29 November an explosion detected at 0611 produced a small pyroclastic flow that traveled 500 m. Another pyroclastic flow at 0955 traveled 1 km W. Gas-and-ash plumes rose 4 km above the crater and drifted SE and W. According to a news article, people in high risk areas on the flanks, in communities such as Cusúa, Juive, Palictahua, and Manzano, evacuated voluntarily.
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.