Viedma (volcano)

Coordinates: 49°22′S 73°19′W / 49.367°S 73.317°W / -49.367; -73.317
Source: Wikipedia, the free encyclopedia.
Viedma
Highest point
Elevation1,500 m (4,900 ft)[1]
Coordinates49°22′S 73°19′W / 49.367°S 73.317°W / -49.367; -73.317[2]
Geography
Viedma is located in Argentina
Viedma
Viedma
Viedma is located in Southern Patagonia
Viedma
Viedma
Viedma (Southern Patagonia)
Last eruption
November 1988[1]

Viedma (Spanish pronunciation: [ˈbjeðma]) 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.[1] 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.

Geography and geomorphology

Viedma is located in the southern Patagonian Andes,[3] southwest of Mount FitzRoy.[4] The lake of the same name lies southwest of the volcano. The area is poorly accessible[2] and the volcanic history poorly known.[3]

Viedma is part of the

lava flows on Cook Island.[5]

Few things are known with certainty about the volcanic edifice of Viedma as it is mostly buried beneath glacial ice[6] and the "Viedma Nunatak" was later revealed to not be a volcano.[7] In 1956 Louis Lliboutry proposed that volcanic activity may occur in fissure vents buried beneath glaciers; between eruptions they would be concealed below the ice;[8] Lliboutry considered dark bands on the ice to be tephra deposits, a view supported by a 1958-1959 expedition that found pumice on the Viedma Glacier.[9] Other reports of volcanic phenomena in the region exist, and the existence of a large caldera beneath the Southern Patagonian Ice Field has been suggested as an explanation for volcanism there.[10]

Viedma Nunatak

The Viedma Glacier and the Viedma Nunatak (centre-right)

The Viedma Nunatak is commonly interpreted to be the site of the volcano,[11] after observations made in 1944-1945 and 1950 by survey flights including controversial sightings of fumaroles which also led to the nunatak becoming known as the "Volcan Viedma";[12][8] but the lack of clear evidence[10] and the difficulty of field sampling has rendered its identification with the Viedma vent contentious.[11]

The nunatak is about 1,500 metres (4,900 ft) high above sea level. Most of the mountain is buried beneath the

metamorphic rocks, including gneiss and schists,[11] and no evidence of magmatic rocks was found in a 1958-1959 expedition.[9]

Different observations have yielded different sizes and numbers of supposed craters; González-Ferrán et al. 1995 reported several craters and calderas with sizes ranging 1.5–4 kilometres (0.93–2.49 mi), while Kobayashi et al. 2010 observed fewer craters and none of them larger than 1.5 kilometres (0.93 mi).[14] These craters were later interpreted as being actually glacial cirques containing tarn lakes.[15]

Geology

Map of the volcanic zones arcs in the Andes, and subducted structures affecting volcanism

Off the southernmost west coast of

Nazca Plate beneath the South American Plate.[18]

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

adakitic owing to the melting of the subducting slab and the interaction of these melts with the crust and mantle.[18]

The

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.[19] The regional basement is formed by these Paleozoic and younger metamorphic and sedimentary rocks as well.[18]

Composition

Viedma like other volcanoes of the Austral Volcanic Zone has erupted andesite and dacite. Phenocrysts include amphibole, biotite, hypersthene and plagioclase; orthoclase, plagioclase and pyroxene also occur as xenoliths. The rocks form a calcalkaline suite,[20] but there is also an adakitic signature.[2] The xenoliths may reflect a crustal contamination of the magma erupted at Viedma.[20]

Eruption history

Tephra attributed to Viedma has been found in the

before present which may originate either on Viedma or on Lautaro.[22]

Viedma has erupted during the

before present may have originated at Viedma, although Aguilera and Lautaro are also candidate source volcanoes.[23] Due to the absence of traces of volcanism at Viedma Nunatak the Global Volcanism Program removed its entry for Viedma in 2019.[7]

Historical

Many observations referring to volcanic activity on the Southern Patagonian Ice Field exist, including reports of ashfalls, layers of tephra on glaciers and columns of smoke rising from the ice.[8]

A subglacial eruption occurred in 1988, depositing ash and pumice on the Viedma Glacier. These materials later gave rise to a lahar.[2] The eruption had melted part of the ice and formed a network of valleys; it was assumed that it had taken place at some point between September and November of that year.[24]

Hazards

There are no major population centres close to any volcano in the Austral Volcanic Zone, and the volcanoes are largely unmonitored. Among the know eruptions are large

air traffic and direct ash damage.[25] Viedma is considered to be Argentina's 10th most dangerous volcano.[26]

See also

References

  1. ^ a b c "Viedma". Global Volcanism Program. Smithsonian Institution. Retrieved 2005-02-15.
  2. ^ a b c d e f Kobayashi et al. 2010, p. 434.
  3. ^ a b c Kilian 1990, p. 301.
  4. ^ Shipton 1960, p. 393.
  5. ^ a b Perucca, Alvarado & Saez 2016, p. 552.
  6. ^ a b Perucca, Alvarado & Saez 2016, p. 553.
  7. ^ a b @SmithsonianGVP (15 August 2019). "Global Volcanism Program" (Tweet) – via Twitter.
  8. ^ a b c Shipton 1960, p. 389.
  9. ^ a b Shipton 1960, p. 391.
  10. ^
    ISSN 0718-2244
    .
  11. ^ a b c Blampied et al. 2012, p. 380.
  12. ^ Lliboutry, Luis (1956). Nieves y glaciares de Chile: fundamentos de glaciologia (in Spanish). Ediciones de la Universidad de Chile. p. 413.
  13. ^ Kobayashi et al. 2010, p. 436.
  14. ^ a b Kobayashi et al. 2010, p. 435.
  15. ^ a b Blampied et al. 2012, p. 381.
  16. ^ Kilian 1990, p. 301,302.
  17. S2CID 140710192
    .
  18. ^
    ISSN 0716-0208
    .
  19. ^ Kobayashi et al. 2010, p. 438.
  20. ^ a b Kilian 1990, p. 303.
  21. ISSN 1040-6182
    .
  22. ISSN 0277-3791
    .
  23. S2CID 129856246
    .
  24. ^ Kilian 1990, p. 302.
  25. ^ Perucca, Alvarado & Saez 2016, p. 557.
  26. ISSN 2610-3540
    .

Sources

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