Report on Tungurahua (Ecuador) — 23 July-29 July 2008
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
23 July-29 July 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, 23 July-29 July 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 during 22-23 July, explosions from Tungurahua were detected by the seismic network. An ash plume rose to an altitude of 9 km (29,500 ft) a.s.l. On 25 July, lahars descended two drainages on the W flank. On 26 July, ash-and-steam plumes drifted NW and SW, and explosions and roaring noises were reported. Nighttime incandescence from the crater was noted. On 27 July, roaring noises accompanied ash plumes that rose to altitudes of 8-10 km (26,200-32,800 ft) a.s.l. Ashfall was reported in areas to the SW. During 27-29 July, incandescence was seen around the crater and blocks rolled 800 m down the flanks. Noises were reported and explosions caused windows to vibrate. Ashfall was reported in areas to the SW.
Geological Summary. 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.