This photograph by an astronaut on the International Space Station highlights the Nevados de Chillán, a large volcanic area near the Chile-Argentina border. In this image, north is to the lower right.
Like other historically active volcanoes in the central Andes, the Nevados de Chillán were created by upwelling magma generated by eastward subduction, as the dense oceanic crust of the Pacific basin dove beneath the less dense continental crust of South America. The rising magmas associated with this type of tectonic environment frequently erupt explosively, forming widespread ash and ignimbrite layers. They can also produce less explosive eruptions, with voluminous lava flows that layer together with explosively erupted deposits to build the classic cone-shaped edifice of a stratovolcano.
The Nevados de Chillán includes three distinct volcanic structures built within three overlapping calderas. The snow-capped volcanic complex sits within the glaciated terrain of the central Andes. Glacial valleys are visible at image upper left, upper right, and lower right. The northwestern end of the chain is occupied by the 3,212 meter (10,538 foot) high Cerro Blanco, also known as Volcán Nevado. The 3,089 meter (10,134 foot) high Volcán Viejo (also known as Volcán Chillan) sits at the southeastern end; this volcano was active during the 17th to 19th centuries. A group of lava domes known as Volcán Nuevo formed to the northwest of Volcán Viejo between 1906 and 1945, followed by an even younger dome complex, Volcán Arrau, that formed between 1973 and 1986 (Volcán Arrau is not shown in the image).
The last reported volcanic activity at Nevados de Chillán took place in 2009, according to the Smithsonian Institution’s Global Volcanism Network. Volcanic activity reports are currently available (in Spanish) from the Servicio Nacional de Geología y Minería of Chile.