Servicio Geológico Colombiano’s (SGC) Observatorio Vulcanológico y Sismológico de Manizales reported that a webcam recorded an ash plume rising from Nevado del Ruiz at 0558 on 29 September. Based on information from the Bogota MWO, the Washington VAAC reported on the same day that an ash plume rose to an altitude of 6.1 km (20,000 ft) a.s.l. and drifted WSW. Later that day ASHTAM reports indicated an ash emission to an altitude of 8.5 km (28,000 ft) a.s.l. and drifted 13 km S, though cloud cover prevented webcam and satellite image views. An ash emission reported by the Bogota MWO rose to an altitude of 6.1 km (20,000 ft) a.s.l. and drifted NE on 3 October. The Alert Level remained at III (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)