The Servicio Geológico Colombiano’s (SGC) Observatorio Vulcanológico y Sismológico de Manizales reported that eruptive activity at Nevado del Ruiz continued during 2-8 December, though weather conditions sometimes obscured visual observations. Seismic data indicated that events associated with fluid movement decreased in both number and intensity compared to the previous week. There were no confirmed ash emissions associated with the signals; gas-and-steam emissions rose as high as 1 km above the summit and drifted in various directions. Seismicity associated with rock fracturing was similar in number and intensity compared to the previous week. The earthquakes were low magnitude (up to M1) and mainly located at depths of 2-9 km below Arenas Crater and below the flanks within 12 km. Seismicity associated with activity at the lava dome was recorded on 4 December. Daily sulfur dioxide emissions fluctuated at low levels. Low-level thermal anomalies at the bottom of the crater were periodically identified in satellite images. The Alert Level remained at Yellow (the second level on a four-level scale).

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)