Emi Koussi

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Emi Koussi
Ultra
Coordinates19°47′33″N 18°32′47″E / 19.79250°N 18.54639°E / 19.79250; 18.54639[2]
Geography
LocationChad
Parent rangeTibesti Mountains
Geology
Age of rockHolocene
Mountain typePyroclastic shield
Last eruptionunknown
Climbing
Easiest routeHike

Emi Koussi (also known as Emi Koussou

Borkou Region of northern Chad. The highest mountain of the Sahara, the volcano is one of several in the Tibesti range, and reaches an elevation of 3,415 metres (11,204 ft), rising 3 km (1.9 mi) above the surrounding sandstone
plains. The volcano is 60–70 kilometres (37–43 mi) wide and has a volume of 2,500 cubic kilometres (600 cu mi).

Two nested calderas cap the volcano, the outer one being about 15 by 11 kilometres (9.3 mi × 6.8 mi) in size. Within it on the southeast side is a smaller caldera known as Era Kohor, about 2 kilometres (1.2 mi) wide and 350 metres (1,150 ft) deep. Numerous lava domes, cinder cones, maars, and lava flows are found within the calderas and along the outer flanks of the shield. Era Kohor contains trona deposits, and Emi Koussi has been studied as an analogue of the Martian volcano Elysium Mons. Emi Koussi was active more than one million years ago, but some eruptions may be more recent, and there is ongoing fumarolic and hot spring activity.

Geography and geomorphology

Emi Koussi lies in

Tedaga language, Emi means "mountains", "massif".[6] The mountain has played an important role in the research and discovery history of the Tibesti.[12]

Emi Koussi rises to a height of 3,415 metres (11,204 ft) on the southern side of the volcano,[13][14] towering 3 kilometres (1.9 mi) above the surrounding terrain.[15] It is considered by some astronauts to be the most recognizable landmark on Earth, as seen from orbit.[15] Supposedly the entire Tibesti can be seen from the northern summits.[16]

Topographic map of the Emi Koussi

It is a

gorges emanate into the caldera.[23] The highest point of Emi Koussi lies on the southern rim of the caldera.[9]

Nested within this combined caldera is the Era Kohor caldera,

lava flows.[1] Debris from explosive eruptions fills the calderas.[25]

The Kohor

lava flows.[18] On the upper sectors of the volcano, lavas are crisscrossed by cracks, which are known as "lappiaz".[26] Sandstone crops out on the terrain surrounding the volcano.[18] North of Emi Koussi lie other volcanoes, such as Tarso Ahon and Tarso Emi Chi,[27] the former of which is connected to Emi Koussi by a narrow ridge.[13]

Geology

Tectonic activity appears to have occurred in the Tibesti already between the Carboniferous and the Cretaceous,[5] that is between 358.9 ± 0.4 and 66 million years ago.[28] During the earliest stage of volcanism on Tibesti, alkali basalts formed large plateaus. Later, the central volcanoes developed on top of these plateaus.[15] Volcanism in Tibesti has been explained with a mantle plume, as has been proposed for other African volcanoes,[29] although recently tectonic effects of the collision between Africa and Europe and their effects at a distance have also been advanced as an explanation.[30]

The oldest rocks below the Tibesti are Precambrian diorites, granites and schists,[27] which are probably of Neoproterozoic age and are differentiated into two units.[30] The volcanic rocks rest on an uplifted basement formed by Cretaceous[5] and Paleozoic sandstone.[15] The latter crop out at the southwestern foot of Emi Koussi, while volcanic rocks dominate north of the volcano, and the Tibesti massif is prevalent east and southeast of Emi Koussi.[27] Older volcanic rocks are exposed in valleys.[31]

Emi Koussi has erupted

groundmass of microliths in erupted rocks.[32] Magma genesis mainly involved fractional crystallization processes.[29] Rocks from Emi Koussi were used as raw material by Neolithic societies of the region.[33]

During the early

gorges by 2,000–2,500 metres (6,600–8,200 ft) elevation.[17] Elleboe wadi originates on Emi Koussi,[38] and several streams on the western flank join into the Enneri Miski which drains southwards and disappears south of the mountains.[39] Small pools of water are found around Emi Koussi.[40]

Eruptive history

Emi Koussi caldera, ASTER

Emi Koussi erupted between 2.4 and 1.3 million years ago;[41] it is considered to be of Pliocene-Quaternary age.[42] The volcano was constructed mainly during the Miocene[17][43] within about one million years.[44] Radiometric dating has yielded ages of 2.42 ± 0.03 - 2.33 ± 0.09 million years ago for the oldest Emi Koussi stage. The third stage has yielded ages of 1.4 ± 0.3 - 1.32 ± 0.2 million years ago;[15][45] formerly Era Kohor was considered to be a Holocene centre.[24]

During the first stage, Emi Koussi erupted trachytes and trachyandesites in the form of ignimbrites and

basaltic lapilli. This was followed in the second stage by trachytic, green or grey ignimbrites, trachytic and phonolitic lava domes and additional basaltic lava flows.[15] The second stage ignimbrites can be found within the northern caldera and on the southern flank of the volcano.[19] The third stage was dominantly phonolitic, with breccia, tuffs and ignimbrites including the Kohor ignimbrite.[15] The various ignimbrites contain fiamme and often look like lava flows.[46] Each stage was accompanied by the formation of a caldera,[19] and basaltic volcanism continued through all three stages.[15] Phreatic explosions associated with Era Kohor have deposited large blocks within the summit caldera,[19] including beautifully coloured syenite blocks.[47]

Quaternary volcanism gave rise to the cones on the slopes of Emi Koussi,[18] and the three maars are the most recent vents in the combined caldera,[19] while long lava flows have been interpreted to be the youngest volcanism at Emi Koussi.[48] The most recent volcanic vents show little erosion.[47] Early in the Pleistocene, erosion took place on the flanks of Emi Koussi,[5] and carbonates were deposited in Era Kohor until recent times.[49][50]

On the southern foot of the volcano,

before present have been obtained by radiocarbon dating on diatom beds which have been penetrated or buried by lava flows.[52]

Climate and vegetation

The Tibesti mountains feature a desert mountain climate. There are no weather stations close to Emi Koussi and the stations at lower elevations likely underestimate precipitation at higher elevations,

periglacial landforms is questionable,[52] although periglacial activity likely occurred in the Pleistocene and may continue to the present-day.[51] Even during the Pleistocene, no part of the mountain had sub-freezing temperatures through the entire year.[55]

A number of diatom species have been identified in sediments left by the Era Kohor lake, including

water milfoil grew around the lake.[36]

Generally, in the Tibesti vegetation occurs in five different belts depending on elevation.

mosses.[62] Oldenlandia and Selaginella species grow at fumaroles.[64] The caldera floor was used as a pasture for camels and goats.[23]

The

endemic on Emi Koussi.[61] The fern Asplenium quezelii was discovered on Emi Koussi and at first thought to be endemic there[65] before it was found to be identical to Asplenium daghestanicum, a species also previously considered to be endemic to Dagestan, more than 3,800 kilometres (2,400 mi) away from Emi Koussi.[66]

Gallery

  • Another view of it from space
    Another view of it from space
  • Calderas of Emi Koussi
    Calderas of Emi Koussi
  • Emi Koussi inner crater
    Emi Koussi inner crater
  • Natron in the inner caldera of Emi Koussi
    Natron in the inner caldera of Emi Koussi
  • Emi Koussi seen from Apollo 7 in October 1968
    Emi Koussi seen from Apollo 7 in October 1968

See also

References

  1. ^ a b c "Emi Koussi". Global Volcanism Program. Smithsonian Institution. Retrieved 3 November 2013.
  2. ^ "Emi Koussi". Peakbagger.com. Retrieved 2021-02-12.
  3. ^ Hellmich 1972, p. 10.
  4. ^ Gourgaud & Vincent 2004, p. 261.
  5. ^ a b c d e f g Malin 1977, p. 908.
  6. ^ a b Pachur & Altmann 2006, p. 88.
  7. ^ Gourgaud & Vincent 2004, p. 262.
  8. ^ Permenter & Oppenheimer 2007, p. 609.
  9. ^ a b Jäkel et al. 1972, p. 118.
  10. JSTOR 1789494
    .
  11. ^ a b c Pachur & Altmann 2006, p. 103.
  12. ^ a b Jäkel et al. 1972, p. 117.
  13. ^ a b c Gèze et al. 1959, p. 137.
  14. ^ a b Messerli & Winiger 1992, p. 327.
  15. ^ a b c d e f g h i j k Gourgaud & Vincent 2004, p. 264.
  16. ^ a b Tilho 1920, p. 172.
  17. ^ a b c Hellmich 1972, p. 21.
  18. ^ a b c d e f g Gourgaud & Vincent 2004, p. 263.
  19. ^ a b c d e f g h Gourgaud & Vincent 2004, p. 267.
  20. ^
    JSTOR 23439749
    .
  21. ^ a b Permenter & Oppenheimer 2007, p. 621.
  22. ^ a b c Hellmich 1972, p. 172.
  23. ^ a b Jäkel et al. 1972, p. 119.
  24. ^ a b Malin 1977, p. 909.
  25. ^ a b Gèze et al. 1959, p. 139.
  26. ^ a b Poli 1974, p. 225.
  27. ^ a b c Permenter & Oppenheimer 2007, p. 616.
  28. ^ "International Chronostratigraphic Chart" (PDF). International Commission on Stratigraphy. August 2018. Archived from the original (PDF) on 31 July 2018. Retrieved 4 December 2018.
  29. ^ a b Gourgaud & Vincent 2004, p. 288.
  30. ^ a b Deniel et al. 2015, p. 3.
  31. ^ Gèze et al. 1959, p. 138.
  32. ^ Gourgaud & Vincent 2004, pp. 268–269.
  33. ISBN 9781468471281
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  34. ^ Pachur & Altmann 2006, p. 159.
  35. ^ a b Pachur & Altmann 2006, p. 119.
  36. ^ a b Hoelzmann, Philipp (2016-01-01). "Crater palaeolakes in the Tibesti mountains (Central Sahara, North Chad) – New insights into past Saharan climates". ResearchGate. EGU2016.
  37. ^ Hellmich 1972, p. 56.
  38. ^ Tilho 1920, p. 171.
  39. ^ a b Dumont 1987, p. 135.
  40. ^ Dumont 1987, p. 141.
  41. ^ Gourgaud & Vincent 2004, p. 266.
  42. ^ Gourgaud & Vincent 2004, p. 268.
  43. ^ Bruneau de Miré & Quézel 1959, p. 135.
  44. ^ Deniel et al. 2015, p. 17.
  45. ^ Deniel et al. 2015, p. 18.
  46. ^ Deniel et al. 2015, p. 8.
  47. ^ a b c Hellmich 1972, p. 22.
  48. ^ Oppenheimer, C. (1997). "Surveillance and Mapping of Volcanoes and their Emissions by Satellite Remote Sensing". Geography. 82 (4): 317–333.
    JSTOR 40572950
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  49. ^ a b Permenter & Oppenheimer 2007, p. 619.
  50. ^ Gèze et al. 1959, p. 165.
  51. ^ a b Dumont 1987, p. 134.
  52. ^ a b c "Hochgebirgsforschung: Tibesti - Zentrale Sahara, Arbeiten aus der Hochgebirgsregion". Zeitschrift für Gletscherkunde und Glazialgeologie. 8. 1972.
  53. ^ Messerli 1973, p. 146.
  54. ^ Messerli 1973, p. 141.
  55. ^ Messerli & Winiger 1992, p. 317.
  56. ^ Pachur & Altmann 2006, p. 137.
  57. ^ Pachur & Altmann 2006, p. 120.
  58. ^ Lézine et al. 2011, p. 1353.
  59. ^ Messerli 1973, p. 142.
  60. ^ Lézine et al. 2011, p. 1354.
  61. ^
    ISSN 1989-1067
    .
  62. ^ a b Poli 1974, p. 226.
  63. ^ Bruneau de Miré & Quézel 1959, p. 136.
  64. doi:10.1080/01811789.1989.10826963
    .
  65. ^ Viane 1987, p. 143.
  66. ^ Viane 1987, p. 147.

Sources

External links

Media related to Emi Koussi at Wikimedia Commons

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