Report on Tungurahua (Ecuador) — 26 September-2 October 2001
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 26 September-2 October 2001
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2001. Report on Tungurahua (Ecuador). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 26 September-2 October 2001. Smithsonian Institution and US Geological Survey.
1.467°S, 78.442°W; summit elev. 5023 m
All times are local (unless otherwise noted)
On 24 September at 1500 an eruption at Tungurahua produced an ash cloud that rose ~2 km above the volcano and drifted to the W and SW. Roaring and the sound of rockfalls were heard in several towns near the volcano. An eruption on 25 September at 1230 produced a mushroom-shaped ash cloud that rose 5 km above the volcano. The lower portion of the plume drifted to the NW, while the higher portion remained fixed. Ash fell in the town of Cotaló. During the evening of the 25th Strombolian activity was observed, with rockfalls and incandescent volcanic fragments travelling to the W and NW flanks of the volcano. After the eruption volcanic activity consisted of low-level emissions of steam, gas, and ash. Small amounts of ash fell in southern Quero.
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.