Report on Cotopaxi (Ecuador) — 9 September-15 September 2015
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 9 September-15 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, 9 September-15 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)
During 1-8 September IG reported that a large number of seismic events were located between 2 and 11 km below Cotopaxi's summit; seismicity consisted of long-period events, very-long-period events, tremor, and volcano-tectonic events. During 5-10 September seismic energy decreased along with the size and ash content of emissions. Analysis of ash samples showed an increase in the proportion of juvenile fragments. During an overflight on 9 September, IG scientists observed an ash plume rising 200-300 m above the crater and drifting W. Infrared measurements revealed that temperatures were well below those measured on 3 September. Glacial melting on the upper flanks continued to produce streams of meltwater on the N flank. Several new cracks in the glaciers were noted. On 11 September tremor was low; gas-and-ash emissions rose 500 m and drifted W. On 12 September gas-and-ash plumes rose 1.5 km and drifted W to NW, causing ashfall in Machachi and El Chaupi. During 14-15 September ash emissions rose 1 km. A news article from 14 September noted that area flights had been re-routed around Cotopaxi to avoid ash plumes; the most affected route was between Quito and Guayaquil.
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.