Report on Tungurahua (Ecuador) — 30 November-6 December 2011
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 30 November-6 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, 30 November-6 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 seismicity has remained the same from the previous week from Tungurahua, but the number of explosions has increased during 30 November-6 December. Incandescent blocks traveled 1 km down the flanks, and roaring noises and sounds resembling "cannon shots" were reported all week. Ashfall was reported from almost all populations near the volcano during the week. Ash plumes rose to altitudes of 1.5-5.0 km (4,920-16,400 ft) and drifted in multiple directions. On the night of 2 December lahars descended into the drainages and ejected incandescent blocks 500 m above the crater.
Seismicity increased on 3 December. During 3-5 December pyroclastic flows descended on the W flanks. Pyroclastic flows were also reported on the NW flank on 4 December, and large explosions occurred at 0130, 0600, and 1330. Significant ashfall was reported in San Juan, Manzano (8 km SW), and Bilbao (8 km W). On 5 December incandescent blocks were ejected 300 m above the crater and gray ash was deposited mainly to the E. On 6 December incandescence and Strombolian activity was observed.
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.