Nevado Ojos del Salado is a compound or multiple volcano, consisting of a massif covering some 70 square kilometers formed of at least a dozen andesitic and dacitic ones intermingled with lava domes and craters. The volcano has never been studied in detail. It has not erupted in historic times, though it exhibits continuing fumarolic acitivity. It is a large volcano, rising from a base at just over 3000 m. It consists of two essentially different units. Subsequently, a large dome of hornblende dacite lavas accumulated, forming the greyish massif on the right side.
Fumarolic activity continues to the present day on the summit of the dome.
The foreground and middle distance is mantled with a plinian pumice fall deposit, creating a very smooth surface. The volcano consists of elongate series of six overlapping craters, trending roughly northeast, with the active, fuming crater located near the center of this cluster. It is about 800 m in diameter and 300 m deep. Grey pumice deposits from the 1993 eruption are visible in this photo, and the margins of some pyroclastic flows can be seen at right center. Remarks Volcan Lascar is the only active volcano that had a part in the selection of sites, it is located on the Southern edge of the Chajnantor plain and to the East of the Salar de Atacama.