According to the Washington VAAC, the Manizales Observatory reported that activity at Nevado del Ruiz increased at 0530 on 18 July, and an ash plume rose to an altitude of 6.1 km (20,000 ft) a.s.l. Weather clouds prevented satellite and webcam views. Later that day the Bogata MWO reported that an ash plume drifted SW at an altitude of 6.1 km (20,000 ft) a.s.l., and a NOTAM detailed an ash plume drifting S at the same altitude.

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: Washington Volcanic Ash Advisory Center (VAAC)