Based on info from Servicio Geológico Colombiano’s (SGC) Observatorio Vulcanológico y Sismológico de Manizales, the Washington VAAC reported that on 26 March ash plumes from Nevado del Ruiz rose to an altitude of 7 km (23,000 ft) a.s.l. On 27 March the observatory reported that at 1029 a gas-and-ash plume rose 1.6 km above the crater rim and drifted E. The emission was associated with a seismic event and was also recorded by a webcam.

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.

Sources: Servicio Geológico Colombiano (SGC), Washington Volcanic Ash Advisory Center (VAAC)