alluvial fan

noun Physical Geography.
a fan-shaped alluvial deposit formed by a stream where its velocity is abruptly decreased, as at the mouth of a ravine or at the foot of a mountain.
Also called alluvial cone.


Origin:
1870–75

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Based on the Random House Dictionary, © Random House, Inc. 2014.
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Collins
World English Dictionary
alluvial fan or alluvial cone
 
n
a fan-shaped accumulation of silt, sand, gravel, and boulders deposited by fast-flowing mountain rivers when they reach flatter land
 
alluvial cone or alluvial cone
 
n

Collins English Dictionary - Complete & Unabridged 10th Edition
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American Heritage
Science Dictionary
alluvial fan   (ə-l'vē-əl)  Pronunciation Key 
A fan-shaped mass of sediment, especially silt, sand, gravel, and boulders, deposited by a river when its flow is suddenly slowed. Alluvial fans typically form where a river pours out from a steep valley through mountains onto a flat plain. Unlike deltas, they are not deposited into a body of standing water.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Encyclopedia Britannica
Encyclopedia

alluvial fan

unconsolidated sedimentary deposit that accumulates at the mouth of a mountain canyon because of a dimunition or cessation of sediment transport by the issuing stream. The deposits, which are generally fan-shaped in plan view, can develop under a wide range of climatic conditions and have been studied in the Canadian Arctic, Swedish Lappland, Japan, the Alps, the Himalayas, and other areas. They tend to be larger and more prominent in arid and semiarid regions, however, and generally are regarded as characteristic desert landforms. This is particularly true in the basin-and-range type of areas of parts of Iran, Afghanistan, Pakistan, the western United States, Chile and Peru, Sinai and western Arabia, and Central Asia, where the basic landscape configuration consists of mountains set against adjacent basins

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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Example sentences
The portion of the crater within the landing area has an alluvial fan likely formed by water-carried sediments.
Repeated debris flows and/or floods deposit sediment at the mouth of a canyon, forming an alluvial fan.
They typically travel at great speeds down steep canyons, but may move slowly across a gentle surface of an alluvial fan.
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