Waw an Namus

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Waw an Namus
Wau-en-Namus, Uau en Namus, Waw an Namous
A white hill within a black depression, with lakes and vegetation at its foot and desert elsewhere
The central cone of Waw an Namus
Highest point
Elevation 470 m (1,540 ft) [1]
Coordinates 24°54′22″N 17°46′19″E / 24.906°N 17.772°E / 24.906; 17.772[1]
Naming
Translation Oasis of Mosquitoes
Geography
Waw an Namus is located in Libya
Waw an Namus
Waw an Namus
Geology
Age of rock Pleistocene[1]
Mountain type Volcano

Waw an Namus (also spelled Wau-en-Namus, Arabic: واو الناموس‎) is a volcano in Libya. Of either Pleistocene or Holocene age, it is located within the eastern Fezzan region. The origin of the volcanism there and at Al Haruj farther north is not clear. Radiometric dating has yielded an age of about 200,000 years ago, but other circumstantial evidence points to a Holocene or even historical formation of the volcano.

Waw an Namus is characterized by a caldera surrounded by an apron of dark tephra, which has a notable colour contrast to the surrounding desert terrain of the Sahara. A smaller crater lies northwest of the Waw an Namus caldera. The caldera itself contains a scoria cone. Several small lakes and associated vegetation are located within the caldera.

Name[edit]

It is also known as Uaw en Namus,[2] Uau en Namus, Wau-en-Namus[3] and Wau Sqair.[4] It means "Oasis of mosquitoes", a reference to the small lakes around it[1] and the numerous mosquitoes that exist at Waw an Namus.[4]

Geography and geomorphology[edit]

The volcano lies within the Sahara, in the eastern Fezzan and was discovered a few decades before 1951.[5] The caravan route between Kufra and Sabha passes by the volcano.[6] Ancient graves have been found at Waw an Namus,[7] the oasis was probably visited by herders and hunters[8] and may have been the source of raw materials,[9] but the place is otherwise uninhabited.[6][10] The landscape around Waw an Namus has been described as "very beautiful".[11]

Waw an Namus is a 100 metres (330 ft) deep and 4 kilometres (2.5 mi) wide caldera, which has a small relief outwards[2] but a steep margin inwards.[7] Its formation involved the removal of over 800,000,000 cubic metres (2.8×1010 cu ft) of rock.[12] Another crater lies 5 kilometres (3.1 mi) northwest from Waw an Namus,[13] that vent is formed by overlapping craters which feature no volcanic rocks and have produced salty mud; this may be a site of phreatic activity.[10]

Within the caldera lies a 140 metres (460 ft) high[14] and 1.3 kilometres (0.81 mi) wide[12] scoria cone[1] constructed out of phreatomagmatic material with a 80 metres (260 ft) deep and 150 metres (490 ft) wide crater. Another crater, now reduced to remnants, is located west of the summit crater of the cone.[2][15] The cone is modified by gullies.[16]

Dark-coloured tephra of basaltic composition has buried the desert sand around the caldera to distances of 10–20 kilometres (6.2–12.4 mi), resulting in a conspicuous colour contrast to the much brighter desert sand.[1] This contrast can be noted even on spaceborne images.[17] The tephra deposit consists of volcanic ash and lapilli[14] and covers a surface of about 300 square kilometres (120 sq mi).[18] 2–150 centimetres (0.79–59.06 in) high waves are formed by the tephra, which in its western part is baked together by mudflows.[7] The tephra deposit is stratified, implying that it was generated by more than one eruption.[13] Trade winds have blown the tephra over 100 kilometres (62 mi) southwestward.[19]

Lakes[edit]

Also within the caldera are three small lakes[1] and additional smaller water bodies,[20] all of which form a semicircle around the northern, eastern and southern flanks of the central cone. One of the lakes is north of the scoria cone, the second southeast and south and the third southwest.[15] These lakes cover a total surface of 0.3 square kilometres (0.12 sq mi) and the water surface reaches 434 metres (1,424 ft) elevation, but with seasonal variations[20] which cause some of the lakebodies to dry up at times.[6] The largest lake has a surface area of 0.146 square kilometres (0.056 sq mi) with a depth of 12.5 metres (41 ft), [21] while the deepest of these waterbodies reaches depths of 15–16 metres (49–52 ft).[22] These lakes, some of which have red colours, give Waw an Namus a multicoloured appearance.[23]

The lakes are probably groundwater-fed, as evaporation in the area greatly exceeds precipitation,[20] with the lakes losing about 1,500,000 cubic metres (53,000,000 cu ft) water per year.[24] Freshwater springs nourish[6] at least one freshwater body[12] and the other warm, saline lakes.[2] Isotope ratio analysis indicates that the water at Waw an Namus is recent water.[19]

Geology[edit]

Waw an Namus is an isolated volcano; farther north lie lava flows of basaltic composition and the Haruj volcanic field,[1] about 70 kilometres (43 mi) distant;[14] sometimes Waw an Namus is considered to be part of Haruj. These in turn are only two out of several large but little known volcanic fields in the Sahara.[2] A number of theories have been proposed to explain the volcanism in the Sahara,[25] such as the activation of ancient crustal lineaments by the collision between Africa and Europe;[26] in the case of Waw an Namus the magmas originated in the mantle at about 130 kilometres (81 mi) depth.[27]

The terrain surrounding Waw an Namus is covered by Quaternary sediments.[2] The basement beneath the volcano is crystalline, and is in turn covered by limestone, marl and the Nubian Sandstone.[15]

Alkali basalts have been identified in the scoria,[14] and the occurrence of foidite have been reported.[28] Minerals contained within these rocks include apatite, clinopyroxene, magnetite, nepheline and olivine, and occasionally melilite and sodalite. The rocks contain xenoliths of harzburgite, lherzolite[29] and peridotite.[2] Sulfur occurs within the crater of the scoria cone,[1] as well as white deposits that may be formed by alunite.[2]

Biology[edit]

Acacias, date palms,[30] doum palms,[6] and tamarisks (including Tamarix tetragyna[31]) grow within the caldera,[30] as well as swamp vegetation to varying degrees.[12] Part of the largest lake is covered with reeds[21] (including Phragmites australis[32]) up to 4 metres (13 ft) high; smaller reeds and tamarisks grow around the saline lake as well.[33]

Animal life includes aquatic birds, flies and mosquitoes,[34] among the birds are the ducks Anas clypeata (Northern shoveler), Anas crecca (Eurasian teal), Anas strepera (Gadwall),[35] as well as Acrocephalus scirpaceus (Eurasian reed warbler), Anthus cervinus (Red-throated pipit), Anthus pratensis (Meadow pipit), Bubulcus ibis (Western cattle egret), Corvus ruficollis (Brown-necked raven), Falco biarmicus (Lanner falcon), Fulica atra (Eurasian coot), Gallinula chloropus (Common moorhen), Luscinia svecica (Bluethroat), Motacilla alba (White wagtail), Oenanthe deserti (Desert wheatear), Passer simplex (Desert sparrow), Phoenicurus ochruros (Black redstart), Phylloscopus collybita (Common chiffchaff), Podyceps nigricollis (Black-necked grebe), Rallus aquaticus (Water rail), Saxicola rubicola (European stonechat) and Tachybaptus ruficollis (Little grebe).[36] The oasis has a rich bird life,[37] and some migratory birds likely use Waw an Namus as an overwintering place.[38]

Cyanophyceae, diatoms and green algae are found in the lake waters.[21] Individual species are the cyanophyceae Anabaena variabilis, Eucapsis alpina, Microcoleus steenstrupii[39] and Pseudoanabaena africana[40] and the diatoms Amphiprora duplex, Amphora coffeaeformis, Amphora duplex, Amphora ocellata, Amphora subtilissima, Amphora veneta, Anomoeoneis sphaerophora, Bacillaria paradoxa, Cocconeis placentula, Cymbella pusilla, Denticula sp., Mastogloia aquilegiae, Melosira goetzeana, Navicula interruptestriata, Nitschia amphibia, Nitzschia hybrida, Nitzschia sigma, Nitzscia iugiformis, Nitzscia richterae, Nitzscia sigma, Rhopalodia gibberula, Rhopalodia musculus, Stephanodiscus astraea and Synedra tabulata.[41] [42]

Eruptive history[edit]

The central scoria cone may be only a few thousand years old,[1] possibly even of historical age.[20] The arid climate may mislead as to its actual age,[1] as there is little erosion in the desert.[2] Early geological studies estimated an age of less than 1,000 - 800 years.[12] Salty muds and rocks erupted by the scoria cone and the crater northwest of the main Waw an Namus caldera must have been emplaced after the last pluvial.[13][10] The Waw an Namus caldera cuts a Holocene drainage system in the Sahara and there is no evidence of Neolithic artifacts at Waw an Namus, further supporting a recent origin of the volcano.[43]

Radiometric dating failed to yield a reliable age for the rocks;[14] only an imprecise age of 690,000 ± 1,100,000 years ago was obtained.[29] Later potassium-argon dating yielded an age of 200,000 ± 9,000 years before present for a lava bomb associated with the central cone.[44] Hot springs are active at Waw an Namus and produce sulfurous water.[18]

See also[edit]

References[edit]

  1. ^ a b c d e f g h i j k "Waw an Namous". Global Volcanism Program. Smithsonian Institution. 
  2. ^ a b c d e f g h i Bardintzeff et al. 2012, p. 1049.
  3. ^ "Waw an Namous". Global Volcanism Program. Smithsonian Institution. , Synonyms & Subfeatures
  4. ^ a b Lautensach & Fischer 1957, p. 303.
  5. ^ Richter 1951, p. 16.
  6. ^ a b c d e Bernacsek, G. M.; Hughes, J. S.; Hughes, R. H. (1992). A directory of African wetlands. IUCN. p. 38. 
  7. ^ a b c Knctsch 1950, p. 49.
  8. ^ Posnansky, Merrick; McIntosh, Roderick (1976). "New Radiocarbon Dates for Northern and Western Africa". The Journal of African History. 17 (2): 178. doi:10.1017/S0021853700001286. ISSN 1469-5138. 
  9. ^ Castelli, Roberto; Cremaschi, Mauro; Gatto, Maria Carmela; Liverani, Mario; Mori, Lucia (25 October 2005). "A PRELIMINARY REPORT OF EXCAVATIONS IN FEWET, LIBYAN SAHARA". Journal of African Archaeology. 3 (1): 81. doi:10.3213/1612-1651-10038. ISSN 2191-5784. (Subscription required (help)). 
  10. ^ a b c Knctsch 1950, p. 50.
  11. ^ Klitzsch 1968, p. 587.
  12. ^ a b c d e Richter 1951, p. 20.
  13. ^ a b c Klitzsch 1968, p. 598.
  14. ^ a b c d e Miller et al. 2012, p. 11.
  15. ^ a b c Pachur & Altmann 2006, p. 128.
  16. ^ Lautensach & Fischer 1957, p. 307.
  17. ^ Verstappen, H.Th; van Zuidam, R.A (January 1970). "Orbital photography and the geosciences — a geomorphological example from the Central Sahara". Geoforum. 1 (2): 37. doi:10.1016/0016-7185(70)90027-8. ISSN 0016-7185. 
  18. ^ a b Klitzsch 1968, p. 597.
  19. ^ a b Pachur & Altmann 2006, p. 129.
  20. ^ a b c d Schwabe & Simonsen 1961, p. 255.
  21. ^ a b c Schwabe & Simonsen 1961, p. 256.
  22. ^ Kanter 1967, p. 20.
  23. ^ Lautensach & Fischer 1957, p. 308.
  24. ^ Klitzsch, Eberhard (1967). "Über den Grundwasserhaushalt der Sahara". Africa Spectrum (in German). 2 (3): 32. JSTOR 40173401. (Subscription required (help)). 
  25. ^ Miller et al. 2012, p. 19.
  26. ^ Bardintzeff et al. 2012, p. 1060.
  27. ^ Miller et al. 2012, p. 23.
  28. ^ Bardintzeff et al. 2012, p. 1052.
  29. ^ a b Miller et al. 2012, p. 13.
  30. ^ a b Kanter 1967, p. 12.
  31. ^ Scholz & Gabriel 1973, p. 176.
  32. ^ Scholz & Gabriel 1973, p. 180.
  33. ^ Kanter 1967, p. 19.
  34. ^ Knctsch 1950, pp. 49-50.
  35. ^ Hering 2009, p. 8.
  36. ^ Hering 2009, pp. 9-18.
  37. ^ Hering 2009, p. 20.
  38. ^ Hering 2009, p. 9.
  39. ^ Schwabe & Simonsen 1961, p. 257.
  40. ^ Schwabe & Simonsen 1961, p. 259.
  41. ^ Schwabe & Simonsen 1961, pp. 263-268.
  42. ^ Schwabe & Simonsen 1961, p. 264.
  43. ^ Pachur & Altmann 2006, p. 130.
  44. ^ Bardintzeff et al. 2012, p. 1054.

Sources[edit]

External links[edit]

Media related to Waw an Namus at Wikimedia Commons