Colima began to erupt during the first week of December. Very viscous lava emerged from two vents in the dome that has covered the summit crater since the late 1950's. Aerial observations revealed that lava extruded from a vent in the E half of the dome flowed down its S flank. Collapse at the end of this lava flow produced small glowing avalanches, visible 30 km away during the night, that moved ~ 2 km downslope to the base of the cone. Less voluminous lava extrusion occurred from a vent in the W half of the dome. Activity was continuing as of 20 January.

No felt earthquakes have been reported, nor were volcanic earthquakes detected during 4 days of monitoring with four portable seismographs near Colima. However, small tremors of unspecified origin were detected.

The present eruption is similar to that of November 1975-June 1976. The most recent dome growth occurred between visits by geologists in December 1979 and February 1981.

Geological Summary. The Colima complex is the most prominent volcanic center of the western Mexican Volcanic Belt. It consists of two southward-younging volcanoes, Nevado de Colima (the high point of the complex) on the north and the historically active Volcán de Colima at the south. A group of late-Pleistocene cinder cones is located on the floor of the Colima graben west and east of the complex. Volcán de Colima (also known as Volcán Fuego) is a youthful stratovolcano constructed within a 5-km-wide scarp, breached to the south, that has been the source of large debris avalanches. Major slope failures have occurred repeatedly from both the Nevado and Colima cones, producing thick debris-avalanche deposits on three sides of the complex. Frequent recorded eruptions date back to the 16th century. Occasional major explosive eruptions have destroyed the summit (most recently in 1913) and left a deep, steep-sided crater that was slowly refilled and then overtopped by lava dome growth.

Information Contacts: S. De la Cruz Reyna and F. Medina, UNAM.