Eruptive activity on the Volcán Arrau peak of the Nevados de Chillán Volcanic Complex in Central Chile.

The Observatorio Volcanológico de Los Andes del Sur of the Servicio Nacional de Geología and Minería in Chile have reported observing activity on the Volcán Arrau peak of the Nevados de Chillán Volcanic Complex. This activity was first observed on 21 December 2017, when a flight over the area observed a fissure within the central crater of the volcano. A second flight on 9 January identified a new lava dome (mound produced by the slow extrusion of viscous lava) on the site of the fissure. This was accompanied by gas and water vapour emissions and a surface temperature of about 480°C.

Emissions from Nevados de Chillán on 9 January 2017. Observatorio Volcanológico de Los Andes del Sur/Municipio de Pinto/Twitter.

The Nevados de Chillán Volcanic Complex comprises three main overlapping volcanoes, Cerro Blanco (or Volcán Nevado),  Volcán Viejo (or Volcán Chillán), and Volcán Nuevo, plus a number of smaller vents, including Santa Gertrudis, Gato, Cerro Blanco, Colcura, Calfú Pichicalfú, Baños, Shangri-La, Nuevo, Arrau, Viejo, Chillán y Pata de Perro, Las Lagunillas and Parador. These volcanoes form an approximate line running roughly northwest to southeast, which first emerged during the Late Pleistocene or Early Holocene.

The approximate location of the Nevados de Chillán Volcanic Complex. Google Maps.

Like other volcanoes in the Andes, the Nevados de Chillán Volcanic Complex is fed by the subduction of the Nazca Plate beneath the South American Place along the west coast of the continent. As the Nazca Plate sinks into the Earth it passes under South America, and at the same time is partially melted by the heat and pressure of the planet's interior. More volatile elements in the melted magma to rise up through the overlying South American Plate, fuelling the volcanoes of the Andes.

The subduction of the Nazca Plate beneath the South American Plate, and how it causes Earthquakes and volcanoes. Pacific Earthquake Engineering Research Center.

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