Report on Tungurahua (Ecuador) — 18 June-24 June 2008
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
18 June-24 June 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, 18 June-24 June 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 18-19 June, ash-and-steam plumes from Tungurahua rose to altitudes of 6-8 km (19,700-26,200 ft) a.s.l. and drifted W, NW, and N. On 18 June, a small explosion was detected by the seismic network, and sounds of blocks rolling down the flanks, roaring noises, and "cannon shots" were reported. On 19 June, ashfall was reported in areas NW and W; in Cotaló, about 8 km NW, ash deposits measured about 2 mm thick. Incandescent material and blocks were ejected 500 m above the summit. Blocks rolled about 1 km down the flanks and roaring noises were reported. On 20 June, clouds inhibited visual observations of the summit. Lahars descended NW, W, and S drainages. A mudflow that traveled SW towards the Puela river carried blocks up to 80 cm in diameter.
On 21 June, two periods of increased seismicity were accompanied by strong ash emissions. The resultant ash plumes rose to altitudes of 8-11 km (26,200-36,100 ft) a.s.l. and drifted W. Intense ashfall was reported in areas within 8 km W and SW of the crater. On 22 June, lahars descended several drainages on the W and S flanks. Steam plumes with small ash content rose to an altitude of 6 km (19,700 ft) a.s.l. and drifted W. Roaring noises vibrated windows in areas to the W. During 23-24 June, seismicity decreased and visual observations were inhibited by clouds.
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.