Report on Tungurahua (Ecuador) — 27 April-3 May 2011
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 27 April-3 May 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, 27 April-3 May 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, although visual observations of Tungurahua were occasionally limited due to cloud cover during 26 April-3 May, ash plumes were noted daily and rose to altitudes of 7-12 km (23,000-39,400 ft) a.s.l. The plumes drifted in multiple directions. Ashfall was reported daily in areas within 8 km NNE, N, NW, W, and SW. On 27 and 29 April and during 1-3 May ashfall was reported in areas farther away including the Tungurahua Observatory (OVT) in Guadalupe (11 km N), Ambato (31 km NW), Mocha (25 km W), and 40 km WSW. Blocks ejected from the crater rolled down the flanks on most days and explosions periodically caused doors and windows to vibrate. On 29 April tremor intensified and Strombolian activity increased. According to news articles, an IG scientist noted that boulders the size of a truck were ejected from the crater, causing impact craters 10 m wide where they fell on the flanks. About 300 people evacuated.
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.