page_title: Alluvial fan
section_title: Formation
hierarchical_section_title: Alluvial fan / Formation
caption_attribution_description: English: A vast alluvial fan blossoms across the desolate landscape between the Kunlun and Altun mountain ranges that form the southern border of the Taklimakan Desert in China’s XinJiang Province. The left side is the active part of the fan, and appears blue from water currently flowing in the many small streams. The image was acquired May 2, 2002, covers an area of 56.6 × 61.3 km, and is centered near 37.4 degrees north, 84.3 degrees east.) A view of Google Maps and county maps in Xinjiang provincial atlas shows that the alluvial fan is formed by the river called Mòlèqiē Hé (莫勒切河) in Chinese (which, of course, is a Chinese "transcription" of a Uyghur name - sometimes transcribed as Molcha River). The fan is located in the western part of the Qiemo County. Français&#160;: Un vaste Cône de déjection se répand sur le paysage désolé qui sépare les chaines montagneuses de Kunlun et d'Altun qui forment la frontière sud de la province chinoise du XinJiang. Le bord gauche du cône est sa partie active, et arbore une couleur bleue due aux nombreux chenaux en eau dui le traversent. Image acquise le 2 mai 2002 et couvrant une zone de 56,6 × 61,3 km, centrée sur les coordonnées 37,4° N et 84,3° est.) Italiano: Un vasto conoide di deiezione si apre a ventaglio nell'area desertica prossimale alle catene montuose dell'Altun e del Kunlun che costituiscono il confine meridionale del bacino idrografico del Tarim nella regione autonoma cinese dello Xinjiang. La parte attiva del reticolo idrografico del conoide appare colorata di blu per la presenza delle acque correnti. L'immagine satellitare, scattata il 2 maggio 2002, copre un'area di 56,6 per 61,3 km di lato, ed è centrata sulle coordinate 37,4° N, 84,3° E (parte occidentale della contea di Qiemo). Türkçe: Alüvyon yelpazesi, suyla taşınan tortuların kanyonların dışına süpürülüp, alçak koniler biçiminde vadilerde birikmesiyle oluşan bir yüzey şeklidir. Dağ yamacından aşağı doğru akan su, akıntı daha düz bir yere ulaştığında biriken kum ve kil birikintilerini toplar.
context_page_description: An alluvial fan is an accumulation of sediments shaped like a section of a shallow cone, with its apex at a point source of sediments, such as a narrow canyon emerging from an escarpment. They are characteristic of mountainous terrain in arid to semiarid climates, but are also found in more humid environments subject to intense rainfall and in areas of modern glaciation. They range in area from less than 1 square kilometre to almost 20,000 square kilometres.
  Alluvial fans typically form where flow emerges from a confined channel and is free to spread out and infiltrate the surface. This reduces the carrying capacity of the flow and results in deposition of sediments. The flow can take the form of infrequent debris flows or one or more ephemeral or perennial streams.
  Alluvial fans are common in the geologic record, such as in the Triassic basins of eastern North America and the New Red Sandstone of south Devon. Such fan deposit likely contain the largest accumulations of gravel in the geologic record.
  Some of the largest alluvial fans are found along the Himalaya mountain front on the Indo-Gangetic plain.
context_section_description: Alluvial fans usually form where a confined feeder channel exits a mountain front or a glacier margin. As the flow exits the feeder channel onto the fan surface, it is able to spread out into wide, shallow channels or to infiltrate the surface. This reduces the carrying power of the flow and results in deposition of sediments.
  Flow in the proximal fan, where the slope is steepest, is usually confined to a single channel (a fanhead trench), which may be up to 30 meters (98 ft) deep. This channel is subject to blockage by accumulated sediments or debris flows, which causes flow to periodically break out of its old channel (nodal avulsion) and shift to a part of the fan with a steeper gradient, where deposition resumes. As a result, normally only part of the fan is active at any particular time, and the bypassed areas may undergo soil formation or erosion. 
  Alluvial fans can be debris-flow-dominated or stream-flow-dominated.
caption: A vast (60 km long) alluvial fan blossoms across the desolate landscape between the Kunlun and Altun mountain ranges that form the southern border of the  Taklamakan Desert in Xinjiang. The left side is the active part of the fan, and appears blue from water flowing in the many small streams
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