Report on Tungurahua (Ecuador) — 28 April-4 May 2004
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 28 April-4 May 2004
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2004. Report on Tungurahua (Ecuador). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 28 April-4 May 2004. Smithsonian Institution and US Geological Survey.
1.467°S, 78.442°W; summit elev. 5023 m
All times are local (unless otherwise noted)
During 27 April to 4 May, emissions of gas and ash continued at Tungurahua. Volcano-tectonic earthquakes on 27 and 28 April preceded a slight increase in the number of sudden explosions at Tungurahua on 30 April. According to a news article, on 1 and 2 May ash fell in the towns of Cotaló and San Juan (W of the volcano). The level of seismicity at Tungurahua decreased on 4 May.
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.