An intermittent gray column composed of water vapor and solfataric gases was observed for 3 hours on the evening of 14 November 1993. A similar, but less intense column was witnessed on 16 November by observers at the Servicio Agrícola Ganadero (Farm Service Office) and the local police station in Maricunga, 30 km from the volcano.

Geological Summary. The world's highest active volcano, Nevados Ojos del Salado, rises to 6,879 m along the Chile-Argentina border. The volcano lies about 20 km south of the road that crosses the international border at Paso de San Francisco. The summit complex, which is elongated in a NE-SW direction and overlies a largely buried caldera, contains numerous craters, pyroclastic cones and andesitic-to-rhyolitic lava domes and has been the source of Holocene lava flows. A major rhyodacitic explosive eruption about 1000-1500 years ago produced pumiceous pyroclastic flows. The most recent eruptive activity appears to have originated along a NNE-trending rift along the summit complex. It involved formation of a thick, viscous lava flow and at least a dozen small cones, lava domes, and explosion craters. No confirmed historical eruptions have been recorded, but the volcano has displayed persistent fumarolic activity, and there was an unconfirmed report of minor gas-and-ash emission in 1993.

Information Contacts: Director, Servicio Informativo del la Oficina Nacional de Emergencia, Santiago.