alluvial fan

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.

alluvial fan

noun

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

alluvial fan

/ 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.

Word History and Origins

Origin of alluvial fan¹

First recorded in 1870–75

Example Sentences

This combination of rainfall and reduced tree cover also increased opportunities for erosion, which spread sediments into a thick blanket known as an alluvial fan.

From Singularity Hub 

Half an hour's walk brought us to Vista Alegre, another little clearing on an alluvial fan in the bend of the river.

From Project Gutenberg

Undoubtedly this alluvial fan had been highly prized in this country of terribly steep hills.

From Project Gutenberg

In their place an extensive delta and alluvial fan have been formed.

From Project Gutenberg

Ancient alluvial fan sequences may also be hydrocarbon reservoirs.

From Project Gutenberg

Steep valleys descend from the higher country to join the main valley and at the mouth of every tributary is an alluvial fan.

From Project Gutenberg