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

It’s a desolate alluvial fan on the southern flanks of the Cady Mountains, where sparkling calcite crystals and pieces of quartz, jasper and agate are continually carried down the slopes by thunderstorms and flash floods.

From Los Angeles Times

In a new study, scientists have for the first time produced a detailed map of one of these paleovalleys, located on the Kings River alluvial fan between Fresno and Selma.

From Los Angeles Times

Perched on a broad alluvial fan dotted with rabbitbrush and Joshua trees, this ragtag community of artists, misanthropes and urban refugees has little time for politicians.

From Los Angeles Times

According to the California Department of Water Resources, the state experiences many types of flooding, including alluvial fan, riverine, coastal, flash, and localized floods, as well as debris flows and tsunamis.

From Los Angeles Times

Summer storms in Death Valley are usually more localized, closing a road or two and maybe causing an alluvial fan to flash flood, Jurado said, calling Friday’s downpour “exceptionally rare.”

From Los Angeles Times