IG reported that during 25 November-1 December seismic activity at Cotopaxi was characterized by volcano-tectonic, hybrid, and long-period events. Seismic signals indicating emissions and explosions were also detected. Although cloud cover often prevented observations, gas-and-steam emissions were visible daily. The plumes contained ash on most days and rose as high as 1 km, drifting W and SW. Lahar descended the Agualongo river during 28-29 November and the Mariscal Sucre river on 29 November.

Geological Summary. The symmetrical, glacier-covered, 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 edifice has been constructed since a major collapse sometime prior to about 5,000 years ago. Pyroclastic flows (often confused in historical accounts with lava flows) have accompanied many explosive eruptions, and lahars have frequently devastated adjacent valleys. Strong 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. Smaller eruptions have been frequent since that time.

Source: Instituto Geofísico-Escuela Politécnica Nacional (IG-EPN)