El Negrillar
El Negrillar, also known as Negros de Aras, is a large volcanic field in the Andes, just south of the Salar de Atacama near the Chile–Argentina border. It covers about 220 square kilometres and has around 100 vents and 98 lava flows. The arid climate has preserved its landforms very well. The field formed in the last 1.5 million years, and the most recent eruption happened about 141,000 years ago.
Most eruptions produced lava flows, with some phreatomagmatic activity where magma interacted with groundwater in the Monturaqui–Negrillar–Tilopozo aquifer. Three vents—Copao, Sandillón and Ruda—erupted in a phreatomagmatic style, and about 7,000 years ago the Socompa debris avalanche partly buried the area.
Geologically, El Negrillar is a monogenetic field, meaning each vent erupted only once. The lava flows are mostly blocky and can reach up to 12 km in length; there are also cinder cones and some maars. Lava chemistry ranges from basaltic andesite to dacite, with calc-alkaline signals and adakite-like features, suggesting deep crustal melting. The magma moved through a network of sills at depths of about 9–19 km, and the total erupted volume is estimated at 1.6–7.6 cubic kilometres.
The field lies in a complex, faulted region within the Central Volcanic Zone of the Andes, driven by the subduction of the Nazca Plate beneath South America. Nearby volcanoes include Socompa, Pular and Aguas Delgadas. Local towns such as Monturaqui, Tilomonte and Tilopozo, along with mines and power lines, are in the area. Monogenetic eruptions can still occur, posing a potential threat to the Salar de Atacama region.
This page was last edited on 3 February 2026, at 16:24 (CET).