Report on Tungurahua (Ecuador) — 25 June-1 July 2003
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 25 June-1 July 2003
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2003. Report on Tungurahua (Ecuador). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 25 June-1 July 2003. Smithsonian Institution and US Geological Survey.
1.467°S, 78.442°W; summit elev. 5023 m
All times are local (unless otherwise noted)
Several ash-cloud producing explosions occurred at Tungurahua during 25 June to 1 July. On 25 June ash fell in the sector of Pillate and in the town of Mocha. According to the Washington VAAC, ash was visible on satellite imagery during the report week, with the highest rising ash cloud reaching ~9.4 km a.s.l. on 27 June. Emissions on 29 June deposited ash in Pillate, and in the towns of Cotaló and Cevallos.
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.