Report on Tungurahua (Ecuador) — 21 May-27 May 2008
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 21 May-27 May 2008
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2008. Report on Tungurahua (Ecuador). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 21 May-27 May 2008. Smithsonian Institution and US Geological Survey.
1.467°S, 78.442°W; summit elev. 5023 m
All times are local (unless otherwise noted)
The IG reported that although visual observations were occasionally limited due to cloud cover during 21-27 May, ash and ash-and-steam plumes, often generated by explosions from Tungurahua, were spotted and rose to altitudes of 5.8-9 km (19,000-29,500 ft) a.s.l. Ash plumes drifted SW, W, and NW and ashfall was reported daily in areas within 8 km downwind. Roaring noises, "cannon shot" noises, and sounds resembling blocks rolling down the flanks were reported. On 22, 25, 26, and 27 May, windows vibrated in nearby areas, including at the Tungurahua Observatory (OVT) in Guadalupe, 11 km N. On 23 May, incandescence at the summit was seen at night. On 27 May, lahars descended a drainage in the Pampas sector to the S.
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.