Английская Википедия:Atakor volcanic field

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Шаблон:Short description Шаблон:Infobox mountain Atakor volcanic field ("Atakor" in Tuareg means "swollen part, knot at the end of something"Шаблон:Sfn) is a volcanic field in Algeria. It lies in the Hoggar mountains and consists of a variety of volcanic features such as lava flows and about 450 individual vents which create a spectacular scenery.

Atakor is one of several large volcanic fields in this mountain range, which sits atop of a domal uplift and has erupted basalt, trachyte and phonolite. Volcanism in Atakor took place in several different phases, beginning 20 million years ago and continuing into the Holocene. Presently there is fumarolic activity.

Geography and geomorphology

The field lies in the Hoggar[1] and the terrain approaches elevations of Шаблон:ConvertШаблон:Sfn although the volcanics form an only superficial cover.Шаблон:Sfn The ground has a desert-like appearance.Шаблон:Sfn The scenery of the volcanic field is considered to be spectacular,[1] with the lava domes and volcanic necks rising above the surrounding terrain.Шаблон:Sfn

The field consists of lava domes, lava flows,[1] maars,Шаблон:Sfn scoria cones and volcanic necks[1] which cover an area of about Шаблон:ConvertШаблон:Sfn with a volume of about Шаблон:Convert of volcanic rock.Шаблон:Sfn Basalts form a Шаблон:Convert thick plateau,Шаблон:Sfn and deep gorges lead up to the volcanic fieldШаблон:Sfn and split the Hoggar Mountains in a number of segments.Шаблон:Sfn Wadis diverge from the Atakor volcanic field;Шаблон:Sfn some of them reached Lake Chad in the past,Шаблон:Sfn others continued through the Grand Erg Oriental towards Chott Melrhir.Шаблон:Sfn

Файл:Tahat matin.jpg
Tahat in the Atakor

There are about 450 recent volcanic centres, of which about 400 are lava domes and 50 small stratovolcanoes,Шаблон:Sfn the latter of which include many recent conesШаблон:Sfn which are accompanied by lava flows whose length reaches Шаблон:Convert.Шаблон:Sfn Among the older volcanoes of Atakor are the peaks Assekrem and Tahat,Шаблон:Sfn the latter of which is the highest summit in the Hoggar.Шаблон:Sfn Some of these volcanoes have craters, including double craters, and others are eroded to the point that only volcanic necks remain,Шаблон:Sfn while lava domes include shapes from steep pillars to short stubby lava flowsШаблон:Sfn and are responsible for much of the field's scenery.Шаблон:Sfn Some of these lava domes and necks penetrated older basaltic layers.Шаблон:Sfn Among the stratovolcanoes is the Oued Temorte cone, which is Шаблон:Convert high, Шаблон:Convert wide and has erupted an over Шаблон:Convert long lava flow. It has also erupted volcanic ash, lapilli and slag.[2]

Файл:Panoramique view from the Assekrem.jpg

Geology

Atakor is one in a group of volcanic fields of the Hoggar around Tamanrasset which include Adrar N' Ajjer, Eg'ere, Manzaz and Tahalra,Шаблон:Sfn and is considered to be part of the Hoggar volcanic province which since 34 million years has covered an area of Шаблон:Convert with Шаблон:Convert of volcanic rocks.Шаблон:Sfn A low-seismic velocity anomaly underpins the Atakor volcanic field in the mantleШаблон:Sfn but does not appear to reflect the existence of a hotspot.Шаблон:Sfn

The basement is formed by Precambrian rocks that form a Шаблон:Convert high swellШаблон:Sfn known as the Hoggar swell,Шаблон:Sfn and is further part of the Neoproterozoic Tuareg shieldШаблон:Sfn and a metacraton formed during the Eburnean orogeny.Шаблон:Sfn The basement crops out in deeply incised valleys,Шаблон:Sfn which in general appear to be younger than the Hoggar volcanism.Шаблон:Sfn Active faults occur throughout the region.Шаблон:Sfn

Atakor has erupted basalts, phonolite and trachyte,[1] the latter two form lava domes.Шаблон:Sfn The basalts are characterized by alkali basalts and basanite and form about 80% of all volcanic rocks in Atakor, with less important occurrences of benmoreite, hawaiite, mugearite and rhyolite.Шаблон:Sfn Phenocrysts in some volcanic rocks include amphibole, clinopyroxene, olivine and zircon.[2] The Taessa lavas from this volcanic complexШаблон:Sfn have a porphyritic texture.Шаблон:Sfn The volcanic rocks appear to ultimately derive from mantle plume melts,Шаблон:Sfn although a tectonic origin resulting from the convergence between African and Europe has also been suggested.Шаблон:Sfn

Eruptive history

Volcanic activity in Atakor occurred 20-12 million years ago,Шаблон:Sfn 6.7 - 4.2 million years ago and 1.95 million years ago until today,Шаблон:Sfn with most volcanic activity taking place during the first episode in the Burdigalian and Serravallian.Шаблон:Sfn The second and the third volcanic phases were also accompanied by substantial ground uplift.Шаблон:Sfn Phonolite and trachyte erupted first and basalts later,[1] although contrary to initial belief the flood basalts are from the oldest Tertiary,[3] and the phonolitic-trachytic volcanism continued after the basaltic activity.Шаблон:Sfn Stratovolcanoes with lava flows are the most recent manifestations of activity in Atakor.[2]

Activity continued in the Holocene, with lava flows covering Holocene features[1] such as 10,000 years old lacustrine sediments,[4] pottery[1] and having a fresh appearance. Tuareg oral tradition of "fire mountains"Шаблон:Sfn appears to recount that Tuareg people observed eruptions.[1] Local heat flow anomalies,[5] rare fumaroles and observed seismicity are further evidence of ongoing volcanism.Шаблон:Sfn

Climate and history

Atakor lies within the tropics (south of the Tropic of Cancer) and at high elevation. Precipitation is more common than in the surrounding desert and during winter it can occur in the form of snow;Шаблон:Sfn at Assekrem annual precipitation is about Шаблон:Convert.Шаблон:Sfn In the past, precipitation was considerably higher than today,Шаблон:Sfn such as during the Villafranchian and the Paleolithic when nivation landforms developed above Шаблон:Convert elevation,Шаблон:Sfn as well as morainesШаблон:Sfn such as at TahatШаблон:Sfn and rock glaciers.[6] A last wet period occurred during the Neolithic.[3]

Vegetation in Atakor is subdivided into several belts, a lower Sudanian belt at Шаблон:Convert elevation with bushes and trees,Шаблон:Sfn a sub-Mediterranean between Шаблон:Convert which includes the olive and a high Mediterranean belt which includes Clematis flammula.Шаблон:Sfn The volcanic field is used as a pasture.Шаблон:Sfn

References

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Sources

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Bibliography

Партнерские ресурсы
Криптовалюты
Магазины
Хостинг
Разное

  1. ↑ 1,0 1,1 1,2 1,3 1,4 1,5 1,6 1,7 1,8 Ошибка цитирования Неверный тег <ref>; для сносок GVP не указан текст
  2. ↑ 2,0 2,1 2,2 Ошибка цитирования Неверный тег <ref>; для сносок Conquéré1968 не указан текст
  3. ↑ 3,0 3,1 Ошибка цитирования Неверный тег <ref>; для сносок RognonMensching1969 не указан текст
  4. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Beccaluva2007 не указан текст
  5. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Lesquer1989 не указан текст
  6. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Reffay1982 не указан текст
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