alluvial fan

American  

noun

Physical Geography.

1. 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.

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alluvial fan British  

noun

1. a fan-shaped accumulation of silt, sand, gravel, and boulders deposited by fast-flowing mountain rivers when they reach flatter land

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alluvial fan Scientific  

/ ə-lo̅o̅′vē-əl /

1. 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.

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Etymology

Origin of alluvial fan

First recorded in 1870–75

Example Sentences

Although the shaking was less intense, Trona’s location on soft sediments that have eroded off a mountainside — known as an alluvial fan — caused the ground to act like quicksand, O’Dell said.

From Los Angeles Times • Jul. 10, 2019

A man stands on an alluvial fan below Tumacacori mountain, a few dozen miles north of here.

From The Guardian • Mar. 1, 2017

As distributary channels fill with sediment, the stream is diverted laterally, and the alluvial fan develops into a cone shape with distributaries radiating from the canyon mouth.

From Textbooks • Jan. 1, 2017

The trip I joined was part of a 67-day, 1,058-mile “first,” paddling the Cuito tributary of the Okavango river, which rises in the Angolan Highlands before tipping through Namibia into the alluvial fan in Botswana.

From The Wall Street Journal • Jul. 30, 2015

Under such circumstances, each heavily loaded stream coming out from beneath the ice must have tended to develop a plain of stratified material near its point of issue—a sort of alluvial fan.

From The Geography of the Region about Devils Lake and the Dalles of the Wisconsin by Atwood, Wallace W.