Report on Tungurahua (Ecuador) — 12 December-18 December 2012
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 12 December-18 December 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, 12 December-18 December 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 1 December there was 47 mm of rainfall on the upper E and NE flanks of Tungurahua, generating lahars that descended the Vazcún drainage on the N flank. Seismic stations began recording signals representing the lahars at 1556, and by 1605 contingency plans were activated to warn people downstream. People at the resort of El Salado had been evacuated by the time the lahars reached the area. The lahar was 6 m deep, carried blocks 1-3 m in diameter, and covered drinking water tanks in some areas.
Seismicity at Tungurahua reported by IG increased during 12-14 December. A large explosion at 1435 on 14 December produced a "cannon shot" sound and shook the ground. An ash-and-steam plume rose 6-7 km and drifted NW. Pyroclastic flows traveled down the SW flank. The Washington VAAC reported that an 11-km-wide detached ash plume was observed in satellite imagery drifting 17 km SE. On 15 December IG reported that an explosion was followed by an ash-and-gas plume that rose 2 km above the crater and drifted S and SE. Small amounts of ash fell in Runtún (6 km NNE).
On 16 December a large explosion generated ash plumes that rose to a maximum height of 7 km and contained lightning. Other explosions generated ash plumes that rose 2 km. Satellite imagery showed ash plumes drifting 140 km NW, and 110 km NE at an altitude of 7.9 km (26,000 ft) a.s.l. Tephra fell in Cotaló (8 km NW), Pondoa (8 km N), Runtún, and Pillate (8 km W), and coarse ash fell in Baños (8 km N), Vascún, and Ulba (NNE). Medium-to-fine-grained ash fell in Palitahua (S), Choglontús (SW), Manzano (8 km SW), Capil, Guadalupe Observatory (11 km N), Cevallos (23 km NW), Tisaleo (29 km NW), Ambato (31 km NW), Patate (NW), Píllaro, Pelileo (8 km N), Salcedo, and Pujilí Latacunga, Rio Verde, Agoyán, and Palora. The larger explosions during the morning produced "cannon shots" that broke a window in a local building, and were followed by pyroclastic flows that descended the SW and NW flanks. During 16-17 December incandescent blocks were ejected from the crater and rolled down the flanks.
On 17 December satellite images showed ash plumes drifting 50-130 km NE, and a dense ash plume drifting over 200 km NE at an altitude of 7 km (23,000 ft) a.s.l. A thermal anomaly was also detected. IG noted that explosions continued to generate ash plumes, but with progressively decreasing ash content. Ash plumes drifted NNE and NE, causing ashfall in communities downwind. According to a news article, some of these communities were evacuated.
The VAAC noted that a thermal anomaly was detected on 18 December. Ash plumes drifted 70 km W and 40 km SW. IG reported that seismicity remained elevated, and two pyroclastic flows traveled at most 3-4 km down the flanks and burned vegetation. Explosions rattled structures and ejected incandescent blocks. Ash plumes rose 2-3 km above the crater and drifted NW, W, and SW. Ash fell in multiple areas, and accumulated between 1 and 2 mm during 17-18 December in Juive (7 km NNW).
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.