Servicio Geológico Colombiano’s (SGC) reported that increased seismicity at Nevado del Ruiz began to be recorded at around 1016 on 2 December and increased further on 3 December. The signals indicated moving fluids within the volcano’s conduit and were associated with gas-and-ash emissions seen from several municipalities in Tolima and Caldas. The gas-and-ash plumes generally rose less than 900 m above the summit and drifted SW but occasionally rose as high as 2.9 km. The Alert Level remained at 3 (Yellow; the second lowest level on a four-color 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)