Servicio Geológico Colombiano’s (SGC) Observatorio Vulcanológico y Sismológico de Manizales reported that eruptive activity at Nevado del Ruiz continued at moderate levels during 5-11 March. Seismic events indicating rock fracturing increased both in number and intensity compared to the previous week. These events were located in areas up to 13 km NW, SSW, and NE from Arenas Crater at depths of 1-10 km. The largest earthquake, a M 1.8, was recorded at 1108 on 7 March and was located 4 km SSW of the crater at a depth of 4 km. Seismicity associated with fluid movement in the conduit decreased in both number and magnitude. These events were mainly associated with ash-and-gas emissions that rose as high as 1.1 km above the summit and up to 2 km as the plume drifted downwind. Several thermal anomalies on the crater floor were identified in satellite data, though they had low-to-moderate values. The Alert Level remained at Yellow (the second level on a four-level scale), and the public was warned to stay out of the restricted areas around Arenas Crater.

Geological Summary. Nevado del Ruiz is a broad, glacier-covered volcano in central Colombia that covers more than 200 km2. Three major edifices, composed of andesitic and dacitic lavas and andesitic pyroclastics, have been constructed since the beginning of the Pleistocene. The modern cone consists of a broad cluster of lava domes built within the caldera of an older edifice. The 1-km-wide, 240-m-deep Arenas crater occupies the summit. The prominent La Olleta pyroclastic cone located on the SW flank may also have been active in historical time. Steep headwalls of massive landslides cut the flanks. Melting of its summit icecap during historical eruptions, which date back to the 16th century, has resulted in devastating lahars, including one in 1985 that was South America's deadliest eruption.

Source: Servicio Geológico Colombiano (SGC)