Report on Tungurahua (Ecuador) — 15 August-21 August 2012
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 15 August-21 August 2012
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2012. Report on Tungurahua (Ecuador). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 15 August-21 August 2012. Smithsonian Institution and US Geological Survey.
1.467°S, 78.442°W; summit elev. 5023 m
All times are local (unless otherwise noted)
IG reported that on 15 August three small explosions from Tungurahua were detected along with continuous tremor. An ash plume rose 1 km above the crater and drifted W, producing ashfall in El Manzano (8 km SW) and Pillate (7 km W). Activity increased the next day, characterized by increased tremor, roaring sounds, and instances of vibrating windows. An ash plume again rose 1 km, drifted W, and produced ashfall in El Manzano and Pillate. On 17 August two long periods of tremor associated with emissions were detected; 10 explosions were also recorded. Periodic clear views of the crater showed continuous steam-and-ash plumes rising 1.5-3 km above the crater and drifting WNW. Ash fell in Pillate and Bilbao (8 km W). Activity significantly increased at 2100, and strong explosions were detected. Cloud cover prevented visual observations.
In the morning of 18 August, satellite images showed a 50-km-long plume drifting NW. A pyroclastic flow deposit on the NW flank was observed with a thermal camera. Steam-and-ash plumes rose 1.5 km and drifted WNW; ashfall was reported in Choglontús (SW), Pillate, and San Juan de Pillate (9 km W). Strong glow from the crater was observed at night, along with incandescent blocks rolling down the top of the cone. A pyroclastic flow descended the NE flank, and a lava flow on the N flank traveled 500 m.
Activity remained elevated on 19 and 20 August; continuous tremor indicating emissions was detected, along with nine explosions on 19 August and five on 20 August. Steam-and-ash plumes rose 1.5-2 km and drifted W and SW. Ash fell in Pillate, Igualata (20 km W), El Santuario, Hualpamba, Cevallos (23 km NW), Quero (20 km NW), Mocha (25 km WNW), Santa Anita, and Tisaleo (29 km NW). Roaring sounds were heard and explosions vibrated windows. Strombolian activity ejected incandescent blocks that landed a few hundred meters away. An overflight on 20 August revealed an 80-m-wide inner crater that contained lava. Blocks had accumulated at the headwaters of streams on the SW, W, and NW flanks. According to a news article, 110 families were evacuated.
On 21 August 16 large explosions were detected and again caused windows to vibrate. Strong "cannon shots" were heard in areas as far as Ambato (40 km NW), Riobamba (30 km S), and Milagro, though roaring noises decreased in intensity and duration compared to the previous few days. Ash plumes rose 1.5-5 km and drifted W, and a pyroclastic flow traveled 2.5 km down the NW flank.
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.