Report on Cotopaxi (Ecuador) — 16 September-22 September 2015
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 16 September-22 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, 16 September-22 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)
On 17 September IG reported that during the previous two weeks activity at Cotopaxi had declined, characterized by a decrease in tremor and less intense gas-and-ash emissions. On 10 September, however, the number of volcano-tectonic events increased. They were mostly located 9-12 km below the summit, although some were as shallow as 4 km. During 19-22 September gas emissions with low ash content rose as high as 1.5 km above the crater and drifted W.
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.