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.

Nearby words

  1. alluringly,
  2. allusion,
  3. allusive,
  4. allusively,
  5. alluvial,
  6. alluvial mining,
  7. alluvial plain,
  8. alluvion,
  9. alluvium,
  10. ally

Origin of alluvial fan

First recorded in 1870–75

Also called alluvial cone. Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

British Dictionary definitions for alluvial fan

alluvial fan

alluvial cone


a fan-shaped accumulation of silt, sand, gravel, and boulders deposited by fast-flowing mountain rivers when they reach flatter land
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Science definitions for alluvial fan

alluvial fan

[ ə-lōōvē-əl ]

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 © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.