Report on Cotopaxi (Ecuador) — 26 August-1 September 2015
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 26 August-1 September 2015
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2015. Report on Cotopaxi (Ecuador). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 26 August-1 September 2015. Smithsonian Institution and US Geological Survey.
0.677°S, 78.436°W; summit elev. 5911 m
All times are local (unless otherwise noted)
According to IG, fieldwork revealed that the volume of material ejected since the onset of the eruption at Cotopaxi was an estimated 56,000 cubic meters on 14 August and 19,500 cubic meters during 15-21 August. Thermal images obtained during overflights on 18 and 26 August revealed a significant increase in the temperatures of emissions (150 degrees Celsius on 26 August) and at different areas in the crater.
Since the onset of continuous tremor on the evening of 22 August there had been very few breaks in ash-and-gas emissions. During 25-31 August ash-and-steam emissions were observed rising at most 2 km above the crater and drifting NW, W, and SW. Based on Washington VAAC reports, IG noted on 26 August that the plume rose as high as 9 km (29,500 ft) a.s.l. Ashfall was reported in a wide area to the WSW, millimeters thick in some areas. During 25-26, 28, and 30-31 August areas reporting ashfall included Manabi (El Carmen, 165 km W), Santo Domingo de los Tsáchilas (95 km NW), Pastocalle, Santa Ana, Cerro Azul, Azachul, Leonidas Plaza (40 km N), Bahia de Caraquez (220 WNW), Charapotó (230 W), Pichincha, Rocafuerte (225 WSW), Machachi (25 km NW), Tambillo (33 km NNW), Aloag (28 km NNW), and Chaupi. The mayor of Sigchos, in the Province of Cotopaxi, noted impacts on livestock, crops, and greenhouses. A small lahar descended the W flank on 28 August. Emissions later in the day on 31 August were mostly water vapor and gas, with low amounts of ash.
Geologic Background. Symmetrical, glacier-clad Cotopaxi stratovolcano is Ecuador's most well-known volcano and one of its most active. The steep-sided cone is capped by nested summit craters, the largest of which is about 550 x 800 m in diameter. Deep valleys scoured by lahars radiate from the summit of the andesitic volcano, and large andesitic lava flows extend to its base. The modern conical edifice has been constructed since a major collapse sometime prior to about 5000 years ago. Pyroclastic flows (often confused in historical accounts with lava flows) have accompanied many explosive eruptions, and lahars have frequently devastated adjacent valleys. The most violent historical eruptions took place in 1744, 1768, and 1877. Pyroclastic flows descended all sides of the volcano in 1877, and lahars traveled more than 100 km into the Pacific Ocean and western Amazon basin. The last significant eruption took place in 1904.