Report on Cotopaxi (Ecuador) — 26 November-2 December 2003
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 26 November-2 December 2003
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2003. Report on Cotopaxi (Ecuador). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 26 November-2 December 2003. Smithsonian Institution and US Geological Survey.
0.677°S, 78.436°W; summit elev. 5911 m
All times are local (unless otherwise noted)
During 10-16 November, seismicity at Cotopaxi was at moderate levels, although it had increased in comparison to previous weeks. During the report period, seismicity was dominated by long-period earthquakes. Since late October volcano-tectonic earthquakes occurred beneath the zone of Pita and beneath the volcano's edifice. These events were less than M 3 and were not felt by the local population.
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.