According to INGEOMINAS, the Observatorio Vulcanológico and Sismológico de Manizales reported that on 4 June observations of Nevado del Ruiz during an overflight and through web cameras located in the vicinity of Arenas Crater revealed that gas-and-ash plumes rose at most 1 km above the crater and drifted W and NW. The next day seismic signals indicated that ash emissions continued. Field observers noted that sulfur dioxide emissions were significant. Based on analysis of satellite imagery, the Washington VAAC reported that an ash plume drifted 40 km W. The VAAC also noted that the Bogota MWO reported ash emissions drifting NNW at an altitude of 9.1 km (30,000 ft) a.s.l. The Alert Level remained at II (Orange; "eruption likely within days or weeks").

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)