The symmetrical Volcán Parinacota is the southernmost and youngest of a pair of volcanoes forming the Nevados de Payachata group along the Chile-Bolivia border. The dominantly Pleistocene Pomerape volcano towers above a low saddle to the NE. Collapse of Parinacota about 8,000 years ago produced a 6 km3 debris avalanche that traveled 22 km W and blocked drainages, forming Lake Chungará. Holocene eruptive activity has subsequently reconstructed the stratovolcano, which contains a pristine, 300-m-wide summit crater and youthful lava flows on the W flanks. Although no historical eruptions are known, Helium surface-exposure dates have been obtained for eruptions during the past two thousand years both from the main cone and the Ajata group of satellite cones and lava flows on the S and SW flanks.