Report on Tungurahua (Ecuador) — 12 July-18 July 2006
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 12 July-18 July 2006
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2006. Report on Tungurahua (Ecuador) (Sennert, S, ed.). Weekly Volcanic Activity Report, 12 July-18 July 2006. Smithsonian Institution and US Geological Survey.
1.467°S, 78.442°W; summit elev. 5023 m
All times are local (unless otherwise noted)
During 12-18 July, eruptive activity at Tungurahua increased. Incandescent blocks rolled 500 m down the flanks and steam emissions with moderate ash content reached heights of 300 m above the crater (17,500 ft a.s.l.) during 11-13 July. On 14 July, a large eruption generated ash clouds that reached heights of 15 km above the summit (66,000 ft a.s.l.). The plume expanded in multiple directions and then drifted predominantly W, SW, and E. Ash accumulated to a maximum thickness of 15 mm in Pillate, about 7 km to the W. At least five pyroclastic flows, the first since 1999, traveled N and NW. The resulting deposits were up to 8 m thick and 20 m wide. At least four lava flows were also observed. Over 3,700 people from seven small villages near the volcano evacuated to nearby towns. On 15 and 16 July, multiple pyroclastic flows reached the area of Cusúa, approximately 7 km NW of the summit. Explosions and pyroclastic flows generated ash clouds that reached heights of 6 km above the volcano (36,200 ft a.s.l.). On 17 July, eruption columns with high ash content reached heights of 5 km above the summit (32,900 ft a.s.l.). On 18 July, moderate explosions produced steam columns that reached maximum heights of 3 km above the crater (26,300 ft a.s.l.). A child died after ash inhalation complicated a heart illness.
Geological Summary. 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 collapsed about 3,000 years ago and produced a large debris-avalanche deposit to the west. The modern glacier-capped stratovolcano (Tungurahua III) was constructed within the landslide scarp. 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.