Report on Tungurahua (Ecuador) — 4 July-10 July 2007
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 4 July-10 July 2007
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2007. Report on Tungurahua (Ecuador). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 4 July-10 July 2007. Smithsonian Institution and US Geological Survey.
1.467°S, 78.442°W; summit elev. 5023 m
All times are local (unless otherwise noted)
During 3-10 July, IG reported that ash plumes from Tungurahua rose to altitudes of 6-7.5 km (19,700-24,600 ft) a.s.l. and drifted mainly SW and W. Ashfall was reported from areas downwind during 4 and 6-9 July. Incandescence was visible at the crater on 4 and 9 July and noises were reported during 4-5, 7, and 10 July. On 8 July, incandescence was again seen at the summit and blocks rolled 500 m down the flanks. On 9 July, two explosions were accompanied by "cannon shots" that vibrated windows at the Tungurahua Observatory (OVT) in Guadalupe, 11 km N. Strombolian activity was observed and blocks rolled 1 km down the flanks. On 10 July, a lahar occurred in a W drainage.
Based on pilot reports, information from IG, and satellite imagery, the Washington VAAC reported that during 9-10 July, ash plumes rose to altitudes of 4.9-7 km (16,000-23,000 ft) a.s.l. and drifted W.
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.