Report on Tungurahua (Ecuador) — 25 April-1 May 2012
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 25 April-1 May 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, 25 April-1 May 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 25-30 April visual observations of Tungurahua were occasionally limited due to cloud cover. On 27 April a steam-and-ash plume rose 200 m above the crater and drifted WNW. On 30 April tremor was detected then followed by an ash plume that rose 4 km above the crater and drifted WNW. Ash fell in Manzano (8 km SW), Choglontus (SW), and Cahuají (8 km SW). At night observers in the SW noted incandescent blocks that that traveled 1.5 km down the flank. On 1 May steam-and-ash plumes drifted W producing ashfall in Bilbao (8 km W), Motilones (W), Cotaló (8 km NW), Pillate (7 km W), Chacuaco, Choglontus, Cahuají, and 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.