Report on Tungurahua (Ecuador) — 11 July-17 July 2012
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 11 July-17 July 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, 11 July-17 July 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 10-12 July explosions from Tungurahua were detected by the seismic network. On 11 July a gas-and-ash plume rose 1 km above the crater and drifted W. Residents reported "cannon shot" sounds, along with sounds resembling blocks rolling down the flanks. Slight ashfall was reported in Bilbao (8 km W). On 12 July gas-and-steam plumes rose 0.3-1 km high and an ash plume rose 1.5 km high. Cloud cover often prevented observations of the volcano during 13-16 July; clear views on the morning of 15 July showed no activity at the crater. A small explosion was detected on 14 July and an explosion on 17 July generated a steam plume with low ash content.
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.