Report on Tungurahua (Ecuador) — 2 July-8 July 2003
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 2 July-8 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, 2 July-8 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)
Following an increase in the frequency of ash emissions at Tungurahua on 26 June, activity decreased on 2 July. On 1 and 2 July ash plumes rose to ~2 km above the volcano and ash fell in several towns near the volcano. In addition, Strombolian activity occurred. Ash from eruptions damaged crops and livestock near the volcano. After the 2nd, mainly gas and steam were emitted from the volcano. A state of emergency was declared on 3 July, and food rations were distributed to residents of the town of Chimborazo. The Alert Level at Tungurahua remained at Yellow in the town of Baños and at Orange for the rest of the population in the high-risk zone, as it has since 5 September 2000.
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.