Weak steam emission from the active Arenas crater produced a white plume 800 m high in January. Volcanic seismicity was at very low levels and tremor was infrequent. A small swarm of high-frequency earthquakes on 2 January caused a peak in seismicity, with high levels of released energy. High-frequency events were centered around Arenas crater and the S flank at 0.5-5 km depths. Deformation measurements showed no significant changes.

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.

Information Contacts: C. Carvajal, INGEOMINAS, Manizales.