Report on Tungurahua (Ecuador) — 24 May-30 May 2006
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 24 May-30 May 2006
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2006. Report on Tungurahua (Ecuador). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 24 May-30 May 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 24-30 May, visual observations of Tungurahua were limited due to heavy cloud cover. On 23 May, an ash plume reported by a pilot reached an altitude of 6.4 km (21,000 ft) a.s.l. A faint plume was visible on satellite imagery that drifted WSW. Slight ashfall was reported to the SW in Puela on 24 May, and the observatory reported a decrease in gas and ash emissions. On 25 May a significant meteorological advisory (SIGMET) indicated an ash plume to an altitude of 5 km (16,500 ft) a.s.l. On 27 and 30 May, the VAAC reported that the Instituto Geofísico observed ash plumes at altitudes of 7.9 km (26,000 ft) a.s.l. and 5 km (16,500 ft) a.s.l., respectively.
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.