Llullaillaco

Llullaillaco ( or ) is a dormant stratovolcano on the border between Argentina (Salta Province) and Chile (Antofagasta Region). It is part of the Llullaillaco National Park and lies in the Puna de Atacama, a region of tall volcanic peaks on a high plateau close to the Atacama Desert, one of the driest places in the world. Its maximum elevation is most commonly given as , making it the second-highest active volcano in the world. Despite its height, it is not clear whether the volcano has any glaciers or merely patches of perennial snow and ice. Between and elevation there is a sparse plant cover, while at lower altitudes the climate is too dry for plants to grow. A species of mouse on Llullaillaco is the vertebrate species living at the highest-known altitude.

The volcano formed during the Pleistocene in two stages, named Llullaillaco I and Llullaillaco II. The oldest rocks are about 1.5 million years old. About 150,000 years ago, the volcano's southeastern flank collapsed, generating a debris avalanche that reached as far as from the summit. During the last stage, three conspicuous lava flows were emplaced on the summit. The youngest-dated rocks are 930 ±140 years old, but there are reports of activity from the 19th century.