Report on Tungurahua (Ecuador) — 16 May-22 May 2001
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 16 May-22 May 2001
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2001. Report on Tungurahua (Ecuador). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 16 May-22 May 2001. 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 slightly at Tungurahua during the week. On 15 May several small eruptions occurred, with the largest sending ash up to 3 km above the summit. Light ash fell in the towns of Cotaló and Bilbao. The Washington VAAC reported that an eruption that began around 1830 on 17 May sent an ash cloud to ~9 km a.s.l. that drifted to the SW. According to IG on 17 and 18 May Tungurahua was not visible due to cloudy conditions, but intense activity was indicated by the high number of long-period earthquakes and seismic signals that may have been associated with eruptions. At 0615 on 19 May an eruption produced an ash cloud that rose ~6.7 km a.s.l. IG warned that lahars might be generated if rainfall mixed with ash deposited on the upper W flanks of the volcano.
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.