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alluvial fan




alluvial fan
Large alluvial fan in the Taklimakan Desert, Xinjiang Province, China
Image source: USGS Landsat Project

A generally fan-shaped area of alluvium (water-borne sediment) deposited by a river when it reaches a plain on lower ground, and the speed of flow of the water is abruptly reduced.

Sand, gravel, and silt are the main constituents of the alluvium, with the coarser material deposited near the head of the fan. Organic matter is also transported, making the soil highly fertile. Valuable minerals such as cassiterite (tin ore, SnO2), diamonds, gold, and platinum are often found in alluvial fans.


Related entry

   • delta


Related categories

   • GEOGRAPHY
   • GEOLOGY AND PLANETARY SCIENCE

Source: U.S. Geological Survey