page_title: Viedma (volcano)
section_title: Geology
hierarchical_section_title: Viedma (volcano) / Geology
caption_attribution_description: Volcanic Zones of the Andes
context_page_description: Viedma is a subglacial volcano whose existence is questionable. It is supposedly located below the ice of the Southern Patagonian Ice Field, an area disputed between Argentina and Chile. The 1988 eruption deposited ash and pumice on the ice field and produced a mudflow that reached Viedma Lake. The exact position of the edifice is unclear, both owing to the ice cover and because the candidate position, the "Viedma Nunatak", does not clearly appear to be of volcanic nature.
context_section_description: Off the southernmost west coast of South America, the Antarctic Plate subducts beneath the South American Plate at a rate of 3 centimetres per year (1.2 in/year). This subduction process is responsible for volcanism in the Austral Volcanic Zone. The Austral Volcanic Zone is one of four volcanic zones in the Andes, the other three are the Northern Volcanic Zone, the Central Volcanic Zone and the Southern Volcanic Zone, all of which are separated from the Austral Volcanic Zone and each other by gaps where no volcanic activity occurs. Unlike the Austral Volcanic Zone, volcanism in these other zones is controlled by the subduction of the Nazca Plate beneath the South American Plate.
  The Austral Volcanic Zone was identified as such in 1976, but some volcanoes were identified and localized later. Owing to their similar composition the three northerly volcanoes Lautaro, Viedma and Aguilera are grouped as the "northern Austral Volcanic Zone". Volcanism in the Austral Volcanic Zone is not well known before the Holocene; it is likely that a lull of volcanism occurred before the Pliocene while the Chile Triple Junction was being subducted in the region. Magmas from the Austral Volcanic Zone are adakitic owing to the melting of the subducting slab and the interaction of these melts with the crust and mantle.
  The basement consists of metamorphic rocks of Paleozoic age. Outcrops of the basement are found around the volcano and could even occur on the edifice that crops out from the glaciers. The regional basement is formed by these Paleozoic and younger metamorphic and sedimentary rocks as well.
caption: Map of the volcanic zones arcs in the Andes, and subducted structures affecting volcanism
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