Reclus (named after Élisée Reclus; sometimes confused with Cerro Mano del Diablo southwest of Reclus), also written as Reclús, is a cinder cone and stratovolcano located in the Southern Patagonian Ice Field, Chile. Part of the Austral Volcanic Zone of the Andes, its summit rises 1,000 metres (3,300 ft) above sea level and is capped by a crater about 1 kilometre (0.62 mi) wide. Close to the volcano lies the Amalia Glacier, which is actively eroding Reclus. The volcano has been active during the late Pleistocene and Holocene. A large eruption – among the largest known in the Austral Volcanic Zone – occurred 15,260–14,373 years before present and released over 5 cubic kilometres (1.2 cu mi) of tephra. This tephra fell out over a large area of Patagonia as far as Tierra del Fuego, and disrupted the ecosystem in the region. Subsequently, further but smaller eruptions occurred during the Pleistocene and Holocene. The last historical eruption was in 1908. The volcano is remote and monitoring began only recently. Two dams are located close to the volcano and might be impacted by future eruptions.
Geography and geology
Regional South of the Chile Triple Junction, the Antarctic Plate subducts beneath the South American Plate at a rate of 2 centimetres per year (0.79 in/year). This subduction process is responsible for volcanic activity in the Austral Volcanic Zone; south of the southernmost volcano of this zone, Fueguino, the subduction gives way to strike-slip faulting. This subduction process is not accompanied by much earthquake activity. Not all volcanism at these latitudes was triggered by subduction; during the Miocene the Chile Rise was subducted here and this caused a temporary pause of the subduction process and the formation of a slab window. During this period, southern Patagonia was subject to extensive basaltic volcanism. Later subduction restarted and the Austral Volcanic Zone was born. Farther north in Chile and Argentina, volcanism occurs as a consequence of the subduction of the Nazca Plate beneath the South America Plate, forming the Central Volcanic Zone in northern Chile and Argentina and the Southern Volcanic Zone in southern Chile and Argentina. These two volcanic zones are separated from each other and the Austral Volcanic Zone by gaps without recent volcanic activity.
Local Reclus is a 1,000 metres (3,300 ft) high pyroclastic cone, featuring a c. 1 kilometre (0.62 mi) wide summit crater and is a small volcano. Seen from above, the volcano has the shape of an egg; the pointy end points due west and consists of 150–200 metres (490–660 ft) thick remnants of dacitic rocks of pre- or inter-glacial age. The rest of the volcano consists of a 2,000 metres (6,600 ft) wide outcrop of violet-reddish-brown pyroclastic material that is in part covered by snow. Traces of glacial erosion are not widespread on the edifice, but a radial pattern of erosional gullys overlays the volcano. In 2019, a 0.26 cubic kilometres (0.062 cu mi) landslide took place on its northeastern flank, which propagated below the Amalia Glacier. Lava and pyroclastics are its principal output. The volcano rises within the cirque of the Amalia Glacier and the glacier is actively eroding Reclus; retreat of the glacier in the 1980s has exposed part of the volcano. Reclus lies about 10 kilometres (6.2 mi) east of the Amalia Fjord. The Southern Patagonian Ice Field and the Cordillera Sarmiento are found in the neighbourhood of Reclus, and Torres del Paine is c. 30 kilometres (19 mi) east of the volcano. Politically, the volcano lies in the commune of Natales. The volcano was at first confused with Cerro Mano del Diablo, a mountain located southwest of Reclus proper and formed by sedimentary rocks; only in 1987 was the volcano's true location discovered. This volcano, like other volcanoes of the Austral Volcanic Zone, is not monitored and lies at considerable distance from human habitation. This remoteness of the volcanoes in the region and the frequently hostile weather conditions often make it difficult to identify volcanoes and their precise location. Reclus is part of the Austral Volcanic Zone, a belt of volcanoes at the southernmost tip of South America which includes six volcanoes: from north to south, Lautaro, Viedma, Aguilera, Reclus, Monte Burney and Fueguino. These volcanoes are not very high, seldom exceeding 3,000 metres (9,800 ft). With the exception of the last they are all stratovolcanoes with glaciers and evidence of Holocene activity; Lautaro erupted in 1959. Activity in the Austral Volcanic Zone has resulted in the widespread deposition of tephra in southernmost South America. All of them have erupted exclusively andesite or dacite; basalts or basaltic andesite are absent in contrast to the Southern Volcanic Zone farther north. These rocks in the case of the Austral Volcanic Zone are all of adakitic character, but there does not appear to be an unifying reason for this chemistry among the various volcanoes. Aguilera, Reclus and Burney are constructed along the eastern margin of the Patagonian Batholith. Metamorphic and sedimentary rocks of Paleozoic-Mesozoic age are also part of the basement. The terrain surrounding Reclus is formed by the volcanic-sedimentary El Quemado and Zapata formations.
Petrology The groundmass of Reclus rocks is compositionally dacite to rhyolite, and contains phenocrysts of amphibole, hornblende, orthopyroxene and plagioclase. Plagioclase and quartz also form xenocrysts. The magmas of Reclus appear to form from slab melts that interacted with the mantle. Tephra records indicate that magma composition changed over time.
Eruptive history Reclus together with Aguilera, Hudson and Monte Burney has been a major source of tephra for the region of Tierra del Fuego and Patagonia. Tephra layers discovered in Laguna Potrok Aike and dated to 63,200 years ago, 44,000–51,000 and c. 34,000 years ago may come from Reclus. However, the potassium content of the 51,000-44,000 tephra seems to correlate more with Lautaro or Viedma. The first post-glacial Reclus tephra in Laguna Potrok Aike was emplaced 15,700 years ago, soon before the R1 eruption. About four eruptions took place during the past 15,000 years that deposited ash in the Torres del Paine region. In general, distinguishing Reclus tephras from these of Aguilera, Lautaro or Viedma is difficult.
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