Report on Cotopaxi (Ecuador) — 31 August-6 September 2005
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 31 August-6 September 2005
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2005. Report on Cotopaxi (Ecuador). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 31 August-6 September 2005. Smithsonian Institution and US Geological Survey.
0.677°S, 78.436°W; summit elev. 5911 m
All times are local (unless otherwise noted)
During 22-28 August, a large number of long-period (LP) and hybrid earthquakes continued to be recorded at Cotopaxi. Increased seismicity was first recorded in late July. Most of the events recorded during the report period were small, and were recorded mainly at stations nearest to the crater. Also, several LP earthquakes correlated with increased activity at fumaroles in the crater. No deformation or surficial changes were observed at the volcano.
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.