Report on Cotopaxi (Ecuador) — November 1975
Natural Science Event Bulletin, vol. 1, no. 2 (November 1975)
Managing Editor: David Squires.
Cotopaxi (Ecuador) Continued vapor emanations in November
Please cite this report as:
Global Volcanism Program, 1975. Report on Cotopaxi (Ecuador) (Squires, D., ed.). Natural Science Event Bulletin, 1:2. Smithsonian Institution.
0.677°S, 78.436°W; summit elev. 5911 m
All times are local (unless otherwise noted)
The activity continued during November. The amount of vapor was about the same as in October, but daily cloud activity was observed. There was increased fumarolic activity on the W side, just below the crater. Earthquakes were felt in the town of Mulaló around 0000, 11 November, and at 0431, 12 November, and again on 14 November. Three portable seismographs were placed around the volcano, and were gathering valuable seismic data by the end of the month.
Geological Summary. 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.
Information Contacts: M. Hall, Escuela Politécnica, Quito.