Report on Tungurahua (Ecuador) — 4 June-10 June 2003
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 4 June-10 June 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, 4 June-10 June 2003. Smithsonian Institution and US Geological Survey.
1.467°S, 78.442°W; summit elev. 5023 m
All times are local (unless otherwise noted)
Volcanic activity increased at Tungurahua around 5 June. On the evening of 6 June Strombolian activity was observed, consisting of incandescent volcanic blocks being hurled ~500 m from the summit. Plumes composed mainly of steam rose to heights around 2 km above the volcano and drifted W. Ash fell in the towns of Pilate, San Juan, and Riobamba, depositing less than 1 mm of ash. According to the Washington VAAC, intense cloud cover prohibited identification of ash plumes on satellite imagery. On the 6th there were reports of ash interfering with main flight routes across Ecuador. IG reported emissions on the 9th reaching 3 km above the volcano and drifting W. On 9 June at 0815 an aircraft reported ash at a height of ~6 km above the volcano. 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.