fbpx
Wikipedia

Emi Koussi

January 01, 1970

Emi Koussi (also known as Emi Koussou[3]) is a high pyroclastic shield[1] volcano that lies at the southeast end of the Tibesti Mountains in the central Sahara, in the northern 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).

Emi Koussi
Emi Koussi seen from space
Highest point
Elevation3,415 m (11,204 ft)[1]
ListingCountry high point
Ultra
Coordinates19°47′33″N 18°32′47″E / 19.79250°N 18.54639°E / 19.79250; 18.54639[2]
Geography
Emi Koussi
Location in Chad
LocationChad
Parent rangeTibesti Mountains
Geology
Age of rockHolocene
Mountain typePyroclastic shield
Last eruptionunknown
Climbing
Easiest routeHike

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 edit

Emi Koussi lies in Chad, Africa, and is part of the Tibesti Mountains[4] as well as its highest peak[5] and thus of the Sahara;[6] many peaks of the Tibesti exceed 2,000 metres (6,600 ft) in height.[5] These mountains are formed by a group of volcanoes that grew on top of a large dome of Earth's surface.[7] Volcanism in this area is poorly studied; as the region is remote and access difficult for political reasons.[8] Dirt roads cross the western and eastern margins of the summit caldera,[9] and according to historical reports the Tibu people lived in its summit caldera[10] and in artificial caves.[11] In the 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 shield volcano with a diameter of 60–70 kilometres (37–43 mi)[15] or 60–80 kilometres (37–50 mi)[12] and an estimated volume of 2,500 cubic kilometres (600 cu mi).[17] The summit of Emi Koussi is formed by two overlapping calderas, which together form a[18] 15-by-11-kilometre (9.3 mi × 6.8 mi) wide[15] elliptical caldera that extends from northwest to southeast.[18] The northern caldera formed first, then the southern caldera which is about 50 metres (160 ft) deeper below the northern one. 400–300-metre (1,310–980 ft) high scarps form the inner margin of the southern caldera,[19] with the floor at an elevation of 2,970 metres (9,740 ft).[20] Before the formation of the calderas, the volcano may have reached a height of 4,000 metres (13,000 ft). Emi Koussi has been compared to a Martian volcano, Elysium Mons.[5][21] The caldera rim is cut by one outlet, the Porte de Modiounga,[22] from which 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,[18] which is 300 metres (980 ft) deep and 2 kilometres (1.2 mi) wide, having the appearance of a giant hole.[19] This caldera is also known as Natron Hole[16] or Trou au Natron.[13] Trachytic lava flows are exposed in its walls,[19] and sodium carbonate has been deposited on its floor,[24] which lies at an elevation of 2,670 metres (8,760 ft)[20] and contains a salt lake.[11] The floor of Era Kohor is thus deep white.[22] Three maars and several scoria cones are also nested within the combined caldera,[19] along with lava domes and lava flows.[1] Debris from explosive eruptions fills the calderas.[25]

The Kohor pumices and two sets of ignimbrites cover the flanks of Emi Koussi,[18] which steepen as they approach the summit.[21] Scoria cones on the slopes are accompanied by 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 edit

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 phonolite, trachyandesite and trachyte,[15] as well as mafic rocks like basanite and tephrite. The erupted rocks define two alkaline suites. Phenocryst chemistry and content varies between the various rocks; among the minerals are alkali feldspar, amphibole, biotite, clinopyroxene, olivine, oxides and plagioclase. Alkali feldspar, apatite, clinopyroxene, olivine, magnetite, mica, nepheline, oxides, plagioclase, quartz, sodalite, titanite and zircon also form the 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 Holocene,[34] Era Kohor was filled with a deep, circular lake.[35] Diatom beds have been found 125 metres (410 ft) above the floor of Era Kohor[36] and in depressions without outlet elsewhere in the caldera,[37] they reach thicknesses of 4–5 metres (13–16 ft).[35] Farther down on the mountain, gullies start appearing at 2,800 metres (9,200 ft) elevation and become deep 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 edit

 
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, fumaroles are active[5] such as at Yi Yerra at 850 metres (2,790 ft) elevation on the southern flanks.[25] At Yi Yerra, hot springs produce water with temperatures of 37 °C (99 °F).[51] Emi Koussi is considered to be a Holocene volcano.[49] Lava flows have buried Holocene diatoms beds in its caldera;[11] dates of 14,790 ± 400 - 12,400 ± 400 years before present have been obtained by radiocarbon dating on diatom beds which have been penetrated or buried by lava flows.[52]

Climate and vegetation edit

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,[39] but based on cloud cover data, a yearly precipitation of 80–120 millimetres (3.1–4.7 in) has been estimated for Emi Koussi;[53] in the past it was wetter than this.[14] The climate reflects both northerly and southerly influences and is distinct from that of the surrounding deserts.[52] There is no evidence of nivation forms on Emi Koussi[54] and the identification of 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 Cocconeis placentula, Cyclotella cyclopuncta, Cyclotella ocellata, Cymbella cistula, Cymbella leptoceros, Cymbella muelleri, Epithemia adnata, Fragilaria construens, Fragilaria pinnata, Gomphonema affine, Gomphonema parvulum, Navicula oblonga and Rhopalodia gibba.[56] The diatom fauna appears to be unusual in comparison to other Saharan paleolakes, probably owing to the high elevation of the Emi Koussi lake.[57] Cattail and water milfoil grew around the lake.[36]

Generally, in the Tibesti vegetation occurs in five different belts depending on elevation.[58] On Emi Koussi, Erica arborea is found up to elevations of 2,900 metres (9,500 ft),[59] in the past it was probably more widespread.[60] The summit region features montane vegetation,[61] including Artemisia-Ephedra steppes[62] which cover large parts of the caldera floor[47] and may have been used as pastures.[22] The lava flows high on the mountain have characteristic environmental traits which allow the development of a particular vegetation.[26][63] This vegetation encompasses Dichrocephala, Eragrostis, Erodium, Helichrysum as well as ferns, liverworts and mosses.[62] Oldenlandia and Selaginella species grow at fumaroles.[64] The caldera floor was used as a pasture for camels and goats.[23]

The wood rush Luzula tibestica is 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 edit

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

See also edit

References edit

  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. ^ Peel, R. F. (1942). "The Tibu Peoples and the Libyan Desert". The Geographical Journal. 100 (2): 73–87. doi:10.2307/1789494. 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. ^ a b Zimmermann, M. (1919). "Chronique Géographique". Annales de Géographie. 28 (155): 387–400. 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. ^ (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. ^ Smith, Andrew (2001). "Saharo-Sudanese Neolithic". Encyclopedia of Prehistory Volume 1: Africa. Springer, Boston, MA. p. 245. doi:10.1007/978-1-4615-1193-9_19. ISBN 9781468471281.
  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.
  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. ^ a b Romo, A.; Boratyński, A. (30 December 2011). "La sección Atlanticae del género Luzula (Juncaceae)". Collectanea Botanica. 30: 55. doi:10.3989/collectbot.2011.v30.005. hdl:10261/50024. ISSN 1989-1067.
  62. ^ a b Poli 1974, p. 226.
  63. ^ Bruneau de Miré & Quézel 1959, p. 136.
  64. ^ Schnell, R. (10 July 2014). "Réflexion sur les flores africaines". Bulletin de la Société Botanique de France. Actualités Botaniques (in French). 136 (3–4): 116. doi:10.1080/01811789.1989.10826963.
  65. ^ Viane 1987, p. 143.
  66. ^ Viane 1987, p. 147.

Sources edit

  • Bruneau de Miré, Ph.; Quézel, P. (1959). "Sur quelques aspects de la Flore residuelle du Tibesti: Les fumeroles du Tousside et les Lappiaz volcaniques cuiminaux de l'Emi Koussi". Bulletin de la Société d'Histoire Naturelle de l'Afrique du Nord (in French). 50.
  • Deniel, C.; Vincent, P. M.; Beauvilain, A.; Gourgaud, A. (1 September 2015). "The Cenozoic volcanic province of Tibesti (Sahara of Chad): major units, chronology, and structural features". Bulletin of Volcanology. 77 (9): 74. Bibcode:2015BVol...77...74D. doi:10.1007/s00445-015-0955-6. ISSN 0258-8900. S2CID 129043535.
  • Dumont, H.J. (1987). "African wetlands and shallow water bodies : region 2 : Sahara" (PDF). Publications scientifiques de l'IRD. Paris: ORSTOM. pp. 79–154. Retrieved 14 April 2018.
  • Gèze, B.; Hudeley, H.; Vincent, P.; Wacrenier, Ph (1 December 1959). "Les volcans du Tibesti (Sahara du Tchad)". Bulletin Volcanologique (in French). 22 (1): 135–172. Bibcode:1959BVol...22..135G. doi:10.1007/BF02596582. ISSN 0366-483X. S2CID 128896369.
  • Gourgaud, A; Vincent, P.M (January 2004). "Petrology of two continental alkaline intraplate series at Emi Koussi volcano, Tibesti, Chad". Journal of Volcanology and Geothermal Research. 129 (4): 261–290. Bibcode:2004JVGR..129..261G. doi:10.1016/S0377-0273(03)00277-4. ISSN 0377-0273.
  • Hellmich, Walter (1972). Hochgebirgsforschung: Tibesti-Zentrale Sahara Arbeiten aus der Hochgebirgsregion (in German). Universitäts-Verlag Wagner.
  • Jäkel, Dieter; Hövermann, Jürgen; Jensch, Georg; Valentin, Hartmut; Wöhlke, Wilhelm (1972). "Arbeitsberichte aus der Forschungsstation Bardai/Tibesti III". Berliner geographische Abhandlungen (in German). 16. doi:10.23689/fidgeo-2849.
  • Lézine, A.-M.; Zheng, W.; Braconnot, P.; Krinner, G. (9 December 2011). "Late Holocene plant and climate evolution at Lake Yoa, northern Chad: pollen data and climate simulations". Clim. Past. 7 (4): 1351–1362. Bibcode:2011CliPa...7.1351L. doi:10.5194/cp-7-1351-2011. ISSN 1814-9332. S2CID 887606.
  • Malin, M. C. (1 July 1977). "Comparison of volcanic features of Elysium (Mars) and Tibesti (Earth)". GSA Bulletin. 88 (7): 908. doi:10.1130/0016-7606(1977)88<908:COVFOE>2.0.CO;2. ISSN 0016-7606.
  • Messerli, B. (1973). "Problems of Vertical and Horizontal Arrangement in the High Mountains of the Extreme Arid Zone (Central Sahara)". Arctic and Alpine Research. 5 (3): A139–A147. JSTOR 1550163.
  • Messerli, B.; Winiger, M. (1992). "Climate, Environmental Change, and Resources of the African Mountains from the Mediterranean to the Equator". Mountain Research and Development. 12 (4): 315–336. doi:10.2307/3673683. JSTOR 3673683.
  • Pachur, H-J.; Altmann, N- (2006). Die Ostsahara im Spätquartär (in German). SpringerLink. doi:10.1007/978-3-540-47625-2. ISBN 978-3-540-47625-2.
  • Permenter, J.L.; Oppenheimer, C. (1 April 2007). "Volcanoes of the Tibesti massif (Chad, northern Africa)". Bulletin of Volcanology. 69 (6): 609–626. Bibcode:2007BVol...69..609P. doi:10.1007/s00445-006-0098-x. ISSN 0258-8900. S2CID 53463999.
  • Poli, E. (1974). "Vegetationsgrenzen in Vulkangebieten". Tatsachen und Probleme der Grenzen in der Vegetation. Bericht über das Internationale Symposion der Internationalen Vereinigung für Vegetationskunde in Rinteln 8.–11. April 1968 (in German). Springer, Dordrecht. pp. 223–251. doi:10.1007/978-94-011-7595-1_21. ISBN 9789401175968.
  • Tilho, J. (1920). "The Exploration of Tibesti, Erdi, Borkou, and Ennedi in 1912-1917: A Mission Entrusted to the Author by the French Institute (Continued)". The Geographical Journal. 56 (3): 161–183. doi:10.2307/1781532. JSTOR 1781532.
  • Viane, R.L.L (1987). "Notes about Asplenium I. Asplenium quezeli, a pseudo-endemic species identical with A. daghestanicum (Aspleniaceae: Pteridophyta)" (PDF). The Fern Gazette. 13 (3). Retrieved 13 April 2018.

External links edit

  • "Emi Koussi Volcano, Chad, North Africa". NASA Earth Observatory. 8 December 2002.
  • . Peakware.com. Archived from the original on 2016-03-04.
  • "Emi Koussi, Chad". Peakbagger.com.

  Media related to Emi Koussi at Wikimedia Commons

January 01, 1970
koussi, also, known, koussou, high, pyroclastic, shield, volcano, that, lies, southeast, tibesti, mountains, central, sahara, northern, borkou, region, northern, chad, highest, mountain, sahara, volcano, several, tibesti, range, reaches, elevation, metres, ris. Emi Koussi also known as Emi Koussou 3 is a high pyroclastic shield 1 volcano that lies at the southeast end of the Tibesti Mountains in the central Sahara in the northern 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 Emi KoussiEmi Koussi seen from spaceHighest pointElevation3 415 m 11 204 ft 1 ListingCountry high pointUltraCoordinates19 47 33 N 18 32 47 E 19 79250 N 18 54639 E 19 79250 18 54639 2 GeographyEmi KoussiLocation in ChadLocationChadParent rangeTibesti MountainsGeologyAge of rockHoloceneMountain typePyroclastic shieldLast eruptionunknownClimbingEasiest routeHike 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 Contents 1 Geography and geomorphology 2 Geology 3 Eruptive history 4 Climate and vegetation 5 Gallery 6 See also 7 References 7 1 Sources 8 External linksGeography and geomorphology editEmi Koussi lies in Chad Africa and is part of the Tibesti Mountains 4 as well as its highest peak 5 and thus of the Sahara 6 many peaks of the Tibesti exceed 2 000 metres 6 600 ft in height 5 These mountains are formed by a group of volcanoes that grew on top of a large dome of Earth s surface 7 Volcanism in this area is poorly studied as the region is remote and access difficult for political reasons 8 Dirt roads cross the western and eastern margins of the summit caldera 9 and according to historical reports the Tibu people lived in its summit caldera 10 and in artificial caves 11 In the 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 nbsp Topographic map of the Emi Koussi It is a shield volcano with a diameter of 60 70 kilometres 37 43 mi 15 or 60 80 kilometres 37 50 mi 12 and an estimated volume of 2 500 cubic kilometres 600 cu mi 17 The summit of Emi Koussi is formed by two overlapping calderas which together form a 18 15 by 11 kilometre 9 3 mi 6 8 mi wide 15 elliptical caldera that extends from northwest to southeast 18 The northern caldera formed first then the southern caldera which is about 50 metres 160 ft deeper below the northern one 400 300 metre 1 310 980 ft high scarps form the inner margin of the southern caldera 19 with the floor at an elevation of 2 970 metres 9 740 ft 20 Before the formation of the calderas the volcano may have reached a height of 4 000 metres 13 000 ft Emi Koussi has been compared to a Martian volcano Elysium Mons 5 21 The caldera rim is cut by one outlet the Porte de Modiounga 22 from which 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 18 which is 300 metres 980 ft deep and 2 kilometres 1 2 mi wide having the appearance of a giant hole 19 This caldera is also known as Natron Hole 16 or Trou au Natron 13 Trachytic lava flows are exposed in its walls 19 and sodium carbonate has been deposited on its floor 24 which lies at an elevation of 2 670 metres 8 760 ft 20 and contains a salt lake 11 The floor of Era Kohor is thus deep white 22 Three maars and several scoria cones are also nested within the combined caldera 19 along with lava domes and lava flows 1 Debris from explosive eruptions fills the calderas 25 The Kohor pumices and two sets of ignimbrites cover the flanks of Emi Koussi 18 which steepen as they approach the summit 21 Scoria cones on the slopes are accompanied by 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 editTectonic 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 phonolite trachyandesite and trachyte 15 as well as mafic rocks like basanite and tephrite The erupted rocks define two alkaline suites Phenocryst chemistry and content varies between the various rocks among the minerals are alkali feldspar amphibole biotite clinopyroxene olivine oxides and plagioclase Alkali feldspar apatite clinopyroxene olivine magnetite mica nepheline oxides plagioclase quartz sodalite titanite and zircon also form the 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 Holocene 34 Era Kohor was filled with a deep circular lake 35 Diatom beds have been found 125 metres 410 ft above the floor of Era Kohor 36 and in depressions without outlet elsewhere in the caldera 37 they reach thicknesses of 4 5 metres 13 16 ft 35 Farther down on the mountain gullies start appearing at 2 800 metres 9 200 ft elevation and become deep 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 edit nbsp 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 fumaroles are active 5 such as at Yi Yerra at 850 metres 2 790 ft elevation on the southern flanks 25 At Yi Yerra hot springs produce water with temperatures of 37 C 99 F 51 Emi Koussi is considered to be a Holocene volcano 49 Lava flows have buried Holocene diatoms beds in its caldera 11 dates of 14 790 400 12 400 400 years before present have been obtained by radiocarbon dating on diatom beds which have been penetrated or buried by lava flows 52 Climate and vegetation editThe 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 39 but based on cloud cover data a yearly precipitation of 80 120 millimetres 3 1 4 7 in has been estimated for Emi Koussi 53 in the past it was wetter than this 14 The climate reflects both northerly and southerly influences and is distinct from that of the surrounding deserts 52 There is no evidence of nivation forms on Emi Koussi 54 and the identification of 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 Cocconeis placentula Cyclotella cyclopuncta Cyclotella ocellata Cymbella cistula Cymbella leptoceros Cymbella muelleri Epithemia adnata Fragilaria construens Fragilaria pinnata Gomphonema affine Gomphonema parvulum Navicula oblonga and Rhopalodia gibba 56 The diatom fauna appears to be unusual in comparison to other Saharan paleolakes probably owing to the high elevation of the Emi Koussi lake 57 Cattail and water milfoil grew around the lake 36 Generally in the Tibesti vegetation occurs in five different belts depending on elevation 58 On Emi Koussi Erica arborea is found up to elevations of 2 900 metres 9 500 ft 59 in the past it was probably more widespread 60 The summit region features montane vegetation 61 including Artemisia Ephedra steppes 62 which cover large parts of the caldera floor 47 and may have been used as pastures 22 The lava flows high on the mountain have characteristic environmental traits which allow the development of a particular vegetation 26 63 This vegetation encompasses Dichrocephala Eragrostis Erodium Helichrysum as well as ferns liverworts and mosses 62 Oldenlandia and Selaginella species grow at fumaroles 64 The caldera floor was used as a pasture for camels and goats 23 The wood rush Luzula tibestica is 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 edit nbsp Another view of it from space nbsp Calderas of Emi Koussi nbsp Emi Koussi inner crater nbsp Natron in the inner caldera of Emi Koussi nbsp Emi Koussi seen from Apollo 7 in October 1968See also editGeography of Chad List of volcanoes in Chad List of Ultras of AfricaReferences edit a b c Emi Koussi Global Volcanism Program Smithsonian Institution Retrieved 3 November 2013 Emi Koussi Peakbagger com Retrieved 2021 02 12 Hellmich 1972 p 10 Gourgaud amp Vincent 2004 p 261 a b c d e f g Malin 1977 p 908 a b Pachur amp Altmann 2006 p 88 Gourgaud amp Vincent 2004 p 262 Permenter amp Oppenheimer 2007 p 609 a b Jakel et al 1972 p 118 Peel R F 1942 The Tibu Peoples and the Libyan Desert The Geographical Journal 100 2 73 87 doi 10 2307 1789494 JSTOR 1789494 a b c Pachur amp Altmann 2006 p 103 a b Jakel et al 1972 p 117 a b c Geze et al 1959 p 137 a b Messerli amp Winiger 1992 p 327 a b c d e f g h i j k Gourgaud amp Vincent 2004 p 264 a b Tilho 1920 p 172 a b c Hellmich 1972 p 21 a b c d e f g Gourgaud amp Vincent 2004 p 263 a b c d e f g h Gourgaud amp Vincent 2004 p 267 a b Zimmermann M 1919 Chronique Geographique Annales de Geographie 28 155 387 400 JSTOR 23439749 a b Permenter amp Oppenheimer 2007 p 621 a b c Hellmich 1972 p 172 a b Jakel et al 1972 p 119 a b Malin 1977 p 909 a b Geze et al 1959 p 139 a b Poli 1974 p 225 a b c Permenter amp Oppenheimer 2007 p 616 International Chronostratigraphic Chart PDF International Commission on Stratigraphy August 2018 Archived from the original PDF on 31 July 2018 Retrieved 4 December 2018 a b Gourgaud amp Vincent 2004 p 288 a b Deniel et al 2015 p 3 Geze et al 1959 p 138 Gourgaud amp Vincent 2004 pp 268 269 Smith Andrew 2001 Saharo Sudanese Neolithic Encyclopedia of Prehistory Volume 1 Africa Springer Boston MA p 245 doi 10 1007 978 1 4615 1193 9 19 ISBN 9781468471281 Pachur amp Altmann 2006 p 159 a b Pachur amp Altmann 2006 p 119 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 Hellmich 1972 p 56 Tilho 1920 p 171 a b Dumont 1987 p 135 Dumont 1987 p 141 Gourgaud amp Vincent 2004 p 266 Gourgaud amp Vincent 2004 p 268 Bruneau de Mire amp Quezel 1959 p 135 Deniel et al 2015 p 17 Deniel et al 2015 p 18 Deniel et al 2015 p 8 a b c Hellmich 1972 p 22 Oppenheimer C 1997 Surveillance and Mapping of Volcanoes and their Emissions by Satellite Remote Sensing Geography 82 4 317 333 JSTOR 40572950 a b Permenter amp Oppenheimer 2007 p 619 Geze et al 1959 p 165 a b Dumont 1987 p 134 a b c Hochgebirgsforschung Tibesti Zentrale Sahara Arbeiten aus der Hochgebirgsregion Zeitschrift fur Gletscherkunde und Glazialgeologie 8 1972 Messerli 1973 p 146 Messerli 1973 p 141 Messerli amp Winiger 1992 p 317 Pachur amp Altmann 2006 p 137 Pachur amp Altmann 2006 p 120 Lezine et al 2011 p 1353 Messerli 1973 p 142 Lezine et al 2011 p 1354 a b Romo A Boratynski A 30 December 2011 La seccion Atlanticae del genero Luzula Juncaceae Collectanea Botanica 30 55 doi 10 3989 collectbot 2011 v30 005 hdl 10261 50024 ISSN 1989 1067 a b Poli 1974 p 226 Bruneau de Mire amp Quezel 1959 p 136 Schnell R 10 July 2014 Reflexion sur les flores africaines Bulletin de la Societe Botanique de France Actualites Botaniques in French 136 3 4 116 doi 10 1080 01811789 1989 10826963 Viane 1987 p 143 Viane 1987 p 147 Sources edit Bruneau de Mire Ph Quezel P 1959 Sur quelques aspects de la Flore residuelle du Tibesti Les fumeroles du Tousside et les Lappiaz volcaniques cuiminaux de l Emi Koussi Bulletin de la Societe d Histoire Naturelle de l Afrique du Nord in French 50 Deniel C Vincent P M Beauvilain A Gourgaud A 1 September 2015 The Cenozoic volcanic province of Tibesti Sahara of Chad major units chronology and structural features Bulletin of Volcanology 77 9 74 Bibcode 2015BVol 77 74D doi 10 1007 s00445 015 0955 6 ISSN 0258 8900 S2CID 129043535 Dumont H J 1987 African wetlands and shallow water bodies region 2 Sahara PDF Publications scientifiques de l IRD Paris ORSTOM pp 79 154 Retrieved 14 April 2018 Geze B Hudeley H Vincent P Wacrenier Ph 1 December 1959 Les volcans du Tibesti Sahara du Tchad Bulletin Volcanologique in French 22 1 135 172 Bibcode 1959BVol 22 135G doi 10 1007 BF02596582 ISSN 0366 483X S2CID 128896369 Gourgaud A Vincent P M January 2004 Petrology of two continental alkaline intraplate series at Emi Koussi volcano Tibesti Chad Journal of Volcanology and Geothermal Research 129 4 261 290 Bibcode 2004JVGR 129 261G doi 10 1016 S0377 0273 03 00277 4 ISSN 0377 0273 Hellmich Walter 1972 Hochgebirgsforschung Tibesti Zentrale Sahara Arbeiten aus der Hochgebirgsregion in German Universitats Verlag Wagner Jakel Dieter Hovermann Jurgen Jensch Georg Valentin Hartmut Wohlke Wilhelm 1972 Arbeitsberichte aus der Forschungsstation Bardai Tibesti III Berliner geographische Abhandlungen in German 16 doi 10 23689 fidgeo 2849 Lezine A M Zheng W Braconnot P Krinner G 9 December 2011 Late Holocene plant and climate evolution at Lake Yoa northern Chad pollen data and climate simulations Clim Past 7 4 1351 1362 Bibcode 2011CliPa 7 1351L doi 10 5194 cp 7 1351 2011 ISSN 1814 9332 S2CID 887606 Malin M C 1 July 1977 Comparison of volcanic features of Elysium Mars and Tibesti Earth GSA Bulletin 88 7 908 doi 10 1130 0016 7606 1977 88 lt 908 COVFOE gt 2 0 CO 2 ISSN 0016 7606 Messerli B 1973 Problems of Vertical and Horizontal Arrangement in the High Mountains of the Extreme Arid Zone Central Sahara Arctic and Alpine Research 5 3 A139 A147 JSTOR 1550163 Messerli B Winiger M 1992 Climate Environmental Change and Resources of the African Mountains from the Mediterranean to the Equator Mountain Research and Development 12 4 315 336 doi 10 2307 3673683 JSTOR 3673683 Pachur H J Altmann N 2006 Die Ostsahara im Spatquartar in German SpringerLink doi 10 1007 978 3 540 47625 2 ISBN 978 3 540 47625 2 Permenter J L Oppenheimer C 1 April 2007 Volcanoes of the Tibesti massif Chad northern Africa Bulletin of Volcanology 69 6 609 626 Bibcode 2007BVol 69 609P doi 10 1007 s00445 006 0098 x ISSN 0258 8900 S2CID 53463999 Poli E 1974 Vegetationsgrenzen in Vulkangebieten Tatsachen und Probleme der Grenzen in der Vegetation Bericht uber das Internationale Symposion der Internationalen Vereinigung fur Vegetationskunde in Rinteln 8 11 April 1968 in German Springer Dordrecht pp 223 251 doi 10 1007 978 94 011 7595 1 21 ISBN 9789401175968 Tilho J 1920 The Exploration of Tibesti Erdi Borkou and Ennedi in 1912 1917 A Mission Entrusted to the Author by the French Institute Continued The Geographical Journal 56 3 161 183 doi 10 2307 1781532 JSTOR 1781532 Viane R L L 1987 Notes about Asplenium I Asplenium quezeli a pseudo endemic species identical with A daghestanicum Aspleniaceae Pteridophyta PDF The Fern Gazette 13 3 Retrieved 13 April 2018 External links edit Emi Koussi Volcano Chad North Africa NASA Earth Observatory 8 December 2002 Emi Koussi Peakware com Archived from the original on 2016 03 04 Emi Koussi Chad Peakbagger com nbsp Media related to Emi Koussi at Wikimedia Commons Retrieved from https en wikipedia org w index php title Emi Koussi amp oldid 1193492673, wikipedia, wiki, book, books, library,

article

, read, download, free, free download, mp3, video, mp4, 3gp, jpg, jpeg, gif, png, picture, music, song, movie, book, game, games.