San Pedro (Chile volcano)

Coordinates: 21°53′16″S 68°23′29″W / 21.88778°S 68.39139°W / -21.88778; -68.39139
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San Pedro
Ultra
Coordinates21°53′16″S 68°23′29″W / 21.88778°S 68.39139°W / -21.88778; -68.39139[2]
Geography
San Pedro is located in Chile
San Pedro
San Pedro
Parent rangeAndes
Geology
Mountain typeStratovolcano
Last eruption1960[2]
Climbing
First ascent16 July 1903; 120 years ago (1903-07-16)
George Courty & Filemón Morales[3]

San Pedro is a

Central Volcanic Zone of the Andes, one of the four tracts of the Andean Volcanic Belt. This region of volcanism includes the world's two highest volcanoes Ojos del Salado and Llullaillaco. San Pedro, like other Andean volcanoes, was formed by the subduction of the Nazca Plate beneath the South America Plate. It has a neighbouring volcano, San Pablo, and is itself formed by two separate edifices usually known as the Old Cone and the Young Cone. These edifices are formed by rocks ranging from basaltic andesite over andesite to dacite and are emplaced on a basement formed by Miocene
volcanic rocks.

The Old Cone was active over one hundred thousand years ago and was eventually truncated by a giant

lava flows and pyroclastic flows constructed the Young Cone as well as the lateral centre La Poruña. This volcano was glaciated during the Pleistocene and a large Plinian eruption occurred at the beginning of the Holocene. Some eruptions reportedly occurred during historical time; presently the volcano is fumarolically
active.

Geography and geomorphology

San Pedro is located in northern Chile, in the

railway station lies southwest of the volcano.[8] Tracks left by sulfur miners lead up to San Pedro's summit,[9][10] and roads run around the volcano;[11] Chile Route 21 [es] passes around the northern, northwestern and western flanks of the volcano.[12]

San Pedro is part of the 600 kilometres (370 mi) long

fumarolic activity.[16]

San Pedro is one of the highest volcanoes in the world

Hydrothermally altered rocks and sulfur deposits are found on San Pedro's summit and were mined into the 1930s.[9]

A number of

lava flows of volumes between 0.1–1.7 cubic kilometres (0.024–0.408 cu mi) make up part of the edifice.[23] The upper part of the Younger Cone is covered with such lava flows, which have steep fronts[2] and are up to 100 metres (330 ft) thick.[24] Downslope the lava flows are found mainly over the northwestern flank where they radiate away from San Pedro's crater.[25] The total volume of the volcano is estimated to be 56 cubic kilometres (13 cu mi).[26]

Scars at elevations of 5,500 metres (18,000 ft) on the edifice have been the origin of

Vesuvius in Italy.[32] This Plinian eruption was accompanied by the formation of an ignimbrite that covers much of the southern, southwestern and western slopes of San Pedro and reaches thicknesses of 3 metres (9.8 ft).[28] It has a volume of 2–15 cubic kilometres (0.48–3.60 cu mi) and is called the El Encanto ignimbrite.[33]

There is evidence of a large sector collapse on San Pedro, which removed the northwestern flank of the volcano and formed a large debris avalanche deposit.[21] This avalanche deposit covers a surface area of 120 square kilometres (46 sq mi) and its front is 35–40 metres (115–131 ft) high[5] in the Pampa de la Avestruz. The debris flow formed by the sector collapse does not have many of the typical hummock-like hills of volcanic sector collapse deposits and instead features grooves and radial ridges.[34] Such flank collapse occurred notably on Mount St. Helens during its eruption in 1980. A 250 metres (820 ft) high scarp west of the eastern summit was left by the collapse of San Pedro; otherwise much of the evidence was buried by later volcanic activity.[21] As with the mudflows, the steep slopes of San Pedro probably facilitated the onset of the sector collapse,[35] which descended over an elevation difference of about 2,845 metres (9,334 ft).[36]

A

lava flows emanate from that area, reaching a considerable distance from the cone. These flows are subdivided into a small proximal unit and two distant ones, and feature structures such as ogives and levees.[39] In addition, a lava dome at an elevation of 5,000 metres (16,000 ft) lies on the southwestern flank of San Pedro and also seems to be a parasitic vent.[23] Andesite lava flows emanate from this area as well. They are the largest found on San Pedro, with volumes of 3 cubic kilometres (0.72 cu mi) and a surface area of 19 square kilometres (7.3 sq mi);[24] they reach a distance of c. 13 kilometres (8.1 mi) from the vent.[40]

San Pedro has been glaciated in the past. Evidence of such glaciation is found especially on the southern side of the Old Cone and it includes moraines at elevations of over 4,400 metres (14,400 ft) as well as other glacially modified surfaces such as rock pavements and striated boulders.[21] The chronology of glaciations in the Central Andes is poorly known but stratigraphic relations indicate that San Pedro was glaciated during the late Pleistocene.[41] There are active rock glaciers on the mountain,[42] with traces of past rock glaciers in cirques on the southern flank ,[43] but there are no glaciers presently on San Pedro.[9]

The

llareta, a plant that was grown as a fuel source.[45]

Geology

Beneath northern Chile, the

Western Cordillera,[46] as well as elsewhere in the Andes.[15]

The volcanoes of Chile are part of the

Austral Volcanic Zone south of the Southern Volcanic Zone.[15]

There were two cycles of volcanic activity in Chile, the first during the Permian-Triassic and a second starting from the Tertiary.[47] In the San Pedro region, this volcanic activity migrated east from its point of inception but recently has moved back westward.[14] West of San Pedro lies the Pampa del Tamarugal and the Coastal Cordillera, neither of which show evidence of recent volcanic activity.[48]

Regional

Volcanoes in this region of Chile often form lineaments perpendicular to the volcanic arc,[47] with northwest–southeast and north–south lineaments common.[49] One such lineament is the c. 65 kilometres (40 mi) long San Pedro-Linzor lineament, which includes San Pedro, Paniri, Cerro Chao, Cerro del León, Toconce and Linzor.[50][51] Other volcanoes with such trends are Carasilla-Polapi-Cerro Cebollar-Cerro Ascotan-Palpana and the Aucanquilcha complex; the youngest edifice is the westernmost one.[52]

The

composite volcanoes[14] and volcanic debris.[53] At least three individual ignimbrites have been found;[5] one of the ignimbrites, the San Pedro Ignimbrite, may have originated from a vent now covered by San Pedro volcano[54] although the neighbouring Caracanal volcano is also a candidate source.[55] The crust in the region is about 70 kilometres (43 mi) thick.[56] The older composite volcano centres include Cerro Carcanal and Cerro Huiche south-southeast of San Pedro and Cerro del Diablo due north.[8] This surface slopes down to the Loa River in the west.[9]

Composition

Old Cone lavas range from

calc-alkaline suite.[23]

San Pedro volcanic rocks are usually glassy with only tiny phenocrysts. Plagioclase and pyroxene are the dominant minerals, with amphibole and olivine being secondary components.[57] The magma feeding the volcano probably formed from the mixing of magmas of distinct temperatures, as indicated by various clues indicating significant thermal disequilibrium between various components.[58] Ultimately they originate in the Altiplano-Puna Magma Body, but undergo storage in shallower crustal magma chambers[59] and absorb crustal gneiss.[60] The eruption of La Poruña appears to have been accompanied by a change in the magma system of the general volcano,[61] a more recent hypothesis regards this cone as a separate volcanic system from San Pedro.[62]

Climate

The region has an

before present by a wetter period during which glaciers expanded.[65] Temperatures strongly fluctuate between day and night; they can go as low as −25 °C (−13 °F) and as high as 25–30 °C (77–86 °F).[64]

Eruptive history

San Pedro formed in two stages, which are known as the Old Cone and the Young Cone. The Old Cone was formed by

argon-argon dating: 160,000 years ago.[5] After activity of the Old Cone ceased, glacial and fluvial erosion dissected San Pedro until the large sector collapse occurred. The so-called "white airfall" with a volume of 2.5 cubic kilometres (0.60 cu mi) as well as pyroclastic flows on the western summit may have been erupted during the collapse but this is uncertain.[21]

Activity of the Young Cone began after the collapse within the scar left by the failure of the edifice. This activity involved the extrusion of four groups of lavas of both andesitic and dacitic composition as well as

argon-argon dating range from 168,000 to 68,000 years ago.[68] The entry of mafic magma at depth about 100,000 years ago may have stimulated the occurrence of eruptions not only at San Pedro but also at neighbouring volcanoes.[69]

A large eruption covered parts of the upper edifice with

radiocarbon years ago[70]). After this event four small lava domes formed in the summit region, and partly underwent collapse forming hot avalanche deposits; it is possible that the 1901 eruption was one of these lava dome forming events.[28]

Historical activity

Eruptions at San Pedro are reported from possibly 1885, when a newspaper from

water pipes.[71] Other eruptions reported from San Pedro were in 1901 when an eruption caused damage,[5] May–August 1910,[72] 1911, February 1938 and a minor event in December 1960. Additional eruptions are mentioned in records and dated to 1870, 1916, 1917, 1923.[2] All these eruptions are uncertain and apparently of phreatic nature,[14] and no geological evidence of them has been found.[73] The timing of eruptions at San Pedro sometimes is unclear; one eruption reported from 1877 may instead have occurred in 1891 as there are two reports of an eruption before 1910 and they may either refer to one eruption with two candidate dates or two eruptions.[72] This volcanic activity makes San Pedro one of the highest active volcanoes.[73]

Presently,

seismic activity has been observed at the volcano,[79] while deformation of the edifice has not been noted.[80]

The history of volcanic activity at San Pedro indicates two principal hazards from future eruptions. The first is the formation of long debris avalanches or

SERNAGEOMIN publishes a volcano hazard level for the volcano.[4]

Climbing

San Pedro is climbed relatively frequently due to its proximity to the tourist town of San Pedro de Atacama. The easiest route is by the north slopes to the col then by the east slope to the summit.[84] It was first climbed by George Courty (France) and Filemón Morales (Chile) July 16, 1903.[3]

  • San Pablo volcano as seen from just below the summit of San Pedro
    San Pablo volcano as seen from just below the summit of San Pedro

See also

References

  1. ^ "San Pedro". Andes Specialists. Archived from the original on 2021-08-17. Retrieved 2020-04-12.
  2. ^ a b c d e f "San Pedro-San Pablo". Global Volcanism Program. Smithsonian Institution.
  3. ^
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  4. ^ a b "San Pedro y San Pablo". www.sernageomin.cl (in Spanish). Sernageomin. Archived from the original on December 15, 2017. Retrieved 2018-02-25.
  5. ^ a b c d e f Bertin & Amigo 2015, p. 1.
  6. ^ a b Zeil 1964, p. 751.
  7. ^ a b "San Pedro y San Pablo". www.sernageomin.cl (in Spanish). Sernageomin. Archived from the original on February 26, 2018. Retrieved 2017-07-09.
  8. ^ a b c d O'Callaghan & Francis 1986, p. 276.
  9. ^ a b c d e Francis et al. 1974, p. 360.
  10. ^ Selles & Gardeweg 2018, p. 63.
  11. ^ Selles & Gardeweg 2018, p. 8.
  12. ^ Selles & Gardeweg 2018, p. 7.
  13. ^ a b Tamburello et al. 2014, p. 4961.
  14. ^ a b c d e f g h i O'Callaghan & Francis 1986, p. 275.
  15. ^
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  16. ^ a b Zeil 1964, p. 736.
  17. ^ Zeil 1964, p. 732.
  18. ^ Tamburello et al. 2014, p. 4962.
  19. ^ a b Casertano 1963, p. 1419.
  20. ^ a b c O'Callaghan & Francis 1986, p. 277.
  21. ^ a b c d e f g h O'Callaghan & Francis 1986, p. 278.
  22. ^ a b Francis et al. 1974, p. 363.
  23. ^ a b c d e f O'Callaghan & Francis 1986, p. 279.
  24. ^ a b c Francis et al. 1974, p. 365.
  25. ^ Francis et al. 1974, p. 362.
  26. ^ Aravena, Diego; Villalón, Ignacio; Pablo, Sánchez. "Igneous Related Geothermal Resource in the Chilean Andes" (PDF). World Geothermal Congress 2015. Retrieved 10 April 2016.
  27. ^ Francis et al. 1974, p. 364.
  28. ^ a b c d Bertin & Amigo 2015, p. 2.
  29. ^ Francis et al. 1974, p. 370.
  30. ^ Francis et al. 1974, p. 368.
  31. ^ Francis et al. 1974, p. 383.
  32. ^ Francis et al. 1974, pp. 373–374.
  33. ^ Selles & Gardeweg 2018, p. 50.
  34. ^ Francis & Wells 1988, p. 279.
  35. ^ a b Francis & Wells 1988, p. 276.
  36. ^ Francis & Wells 1988, p. 260.
  37. ^ Zeil 1964, p. 756.
  38. ^ González-Maurel et al. 2019, p. 5.
  39. ^ Marín et al. 2020, p. 5.
  40. ^ Delunel et al. 2016, p. 73.
  41. ^ Selles & Gardeweg 2018, p. 46.
  42. ISSN 0260-3055
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  43. ^ Payne 1998, p. 5.
  44. ^ Selles & Gardeweg 2018, p. 43.
  45. JSTOR 208707
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  46. ^ a b Payne 1998, p. 3.
  47. ^ a b c Casertano 1963, p. 1415.
  48. ^ Zeil 1964, p. 733.
  49. ^ Zeil 1964, p. 731.
  50. ^ Godoy et al. 2020, p. 2.
  51. ^ Godoy et al. 2014, p. 26.
  52. ^ Francis et al. 1974, p. 382.
  53. ^ Selles & Gardeweg 2018, p. 6.
  54. ^ Francis et al. 1974, p. 373.
  55. ^ Selles & Gardeweg 2018, p. 18.
  56. ^ Godoy et al. 2014, p. 25.
  57. ^ O'Callaghan & Francis 1986, pp. 281–283.
  58. ^ O'Callaghan & Francis 1986, p. 284.
  59. ^ Godoy et al. 2020, p. 3.
  60. ^ Godoy et al. 2014, p. 38.
  61. ^ González-Maurel et al. 2019, p. 16.
  62. ^ a b Marín et al. 2020, p. 2.
  63. ^ Delunel et al. 2016, p. 72.
  64. ^ a b Marín et al. 2020, p. 13.
  65. ^ Payne 1998, p. 4.
  66. ^ Marín et al. 2020, p. 16.
  67. ^ Delunel et al. 2016, p. 78.
  68. ^ González-Maurel et al. 2019, p. 6.
  69. ^ Godoy et al. 2020, p. 9.
  70. ^ Payne 1998, p. 6.
  71. ^ Martin, O. (1897). Revista chilena de historia natural (in Spanish). Museum of Comparative Zoology Harvard University. Valparaíso : Litografia e Impr. Industrial (F. Peters). p. 244. {{cite book}}: Unknown parameter |agency= ignored (help)
  72. ^ a b Casertano 1963, pp. 1421–1422.
  73. ^ a b "San Pedro y San Pablo". www.sernageomin.cl (in Spanish). Sernageomin. Archived from the original on February 26, 2018. Retrieved 2017-07-09., PDF file
  74. ^ Selles & Gardeweg 2018, p. 52.
  75. S2CID 129450763
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  76. ^ Tamburello et al. 2014, p. 4964.
  77. ^ Zeil 1964, p. 752.
  78. JSTOR 1774025. Archived
    from the original on 2024-02-04. Retrieved 2020-09-07.
  79. doi:10.1016/j.jvolgeores.2014.05.004
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  80. S2CID 18453316
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  81. ^ Bertin & Amigo 2015, p. 3.
  82. ISSN 0717-7305. Archived from the original
    (PDF) on June 29, 2021. Retrieved 20 August 2021.
  83. Bibcode:2010AGUFM.V21D2353M
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  84. ^ Biggar, John (2020). The Andes - A Guide for Climbers and Skiers (5th ed.). Scotland. p. 201.{{cite book}}: CS1 maint: location missing publisher (link)

Sources

External links

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