Report on Tungurahua (Ecuador) — 30 July-5 August 2008
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 30 July-5 August 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, 30 July-5 August 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 30-31 July and 2-5 August, explosions from Tungurahua were detected by the seismic network. Although clouds occasionally prevented visual observations, ash plumes were observed that rose to altitudes of 6-9 km (19,700-29,500 ft) a.s.l. and drifted NW, W, and SW. On 30 July, explosions and noises resembling blocks rolling down the flanks were reported. Incandescence at the crater was noted on 31 July. On 31 July and 3 and 4 August blocks rolled up to 1 km down the flanks and ashfall was reported in areas to the SW and W. During 3-4 August, roaring noises were reported in multiple areas. On 4 August an explosion produced an ash plume that rose to an altitude of 13 km (42,700 ft) a.s.l. Intense ashfall was reported in areas W. The noise generated by the explosion was heard as far away as Ambato, 31 km NW.
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.