IG reported that moderate eruptive activity continued at Cotopaxi during 23-30 May. Seismic activity was mainly characterized by long-period earthquakes and tremors associated with emissions that occurred almost daily; a total of three volcanic-tectonic earthquakes were recorded during the week. Weather clouds often hindered views, though gas-and-steam emissions were visible daily. During 23-24 May ash-and-gas emissions rose as high as 1 km above the summit and drifted W. On 26 May a period of continuous ash emissions was recorded with the plumes rising as high as 2 km above the summit and drifting NW and W. On 30 May ash plumes rose 1.2 km and drifted W; ashfall was reported in the Pastocalle parish of Latacunga canton (Cotopaxi Province). Servicio Nacional de Gestión de Riesgos y Emergencias (SNGRE) maintained the Alert Level at Yellow (the second lowest level on a four-color scale).

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.

Sources: Instituto Geofísico-Escuela Politécnica Nacional (IG-EPN), Servicio Nacional de Gestión de Riesgos y Emergencias (SNGRE)