Report on Tungurahua (Ecuador) — 2 October-8 October 2002
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
2 October-8 October 2002
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2002. Report on Tungurahua (Ecuador). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 2 October-8 October 2002. Smithsonian Institution and US Geological Survey.
1.467°S, 78.442°W; summit elev. 5023 m
All times are local (unless otherwise noted)
A relatively large eruption at Tungurahua on 2 October at 0828 produced an ash cloud that rose to a maximum height of ~14.3 km a.s.l. By 1115 on the 2nd the high-level plume had detached from the volcano and there were two areas of ash visible in satellite imagery; one was at ~14.3 km a.s.l. and the other was at ~7.6 km a.s.l. By 1745 no ash was detected on satellite imagery, however, ash was reported SW of Tungurahua over the town of Riobamba at 1700. According to a news report, ashfall was reported in the region NW of the volcano around the towns of Ambato and Patate. IG reported that activity decreased on the morning of 3 October and visible satellite imagery did not reveal any ash in the vicinity of the volcano. The same day an ash cloud was produced to a height of ~7 km a.s.l. Orange Alert Level was in effect for the W side of the volcano, while a lower Yellow Alert Level was in effect in Baños at the northern base of the volcano.
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 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.