The world's highest permanent human habitation is situated below a sulfur mine at the summit region of Cerro Aucanquilcha, one the largest volcanoes of northern Chile. Several distinct cones are located along a 10-km-long, E-W-trending ridge that forms the broad summit of the 6176-m-high stratovolcano. A Pleistocene debris-avalanche deposit is a prominent feature on the lower NW flank. Extensive Pleistocene glacial moraines surround the volcano, but postglacial lava flows overlie these moraines on the upper southern flanks (de Silva and Francis, 1991). Wörner et al. (2000) obtained surprisingly old Potassium-Argon dates of from 400,000 to 780,000 years on the youngest flows of the volcano on the NE and SW flanks, and eruptive activity appears to have ended during the late Pleistocene. Aucanquilcha presently displays fumarolic activity.