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What Is a Fan-Shaped Landform?

In western China, a vast fan-shaped landform spreads across the Taklimakan Desert. Covering an area of approximately 3,400 square kilometers -- slightly smaller than Rhode Island -- this alluvial fan demonstrates the power of flowing water to form intricate and beautiful features across the landscape. Other types of fan-shaped formations occur across the world as sediment is deposited by water, glaciers, wind and even gravity.
  1. Alluvial Fan

    • An alluvial fan occurs where a stream flowing through a narrow valley enters a flatter area. Sediment carried by the water settles out as the water slows down. The sediment builds up in the stream channel and forces the flowing water to create new channels. As this continues, the sedimentary deposits eventually form a fan shape. Besides the one in the Taklimakan Desert, examples of alluvial fans can be seen in Death Valley and Grand Canyon national parks.

    River Delta

    • Like the alluvial fan, a delta -- also known as an arcuate delta -- is a fan-shaped structure created by flowing water. In this case, however, it occurs where a river or stream enters a larger body of water, such as a lake or ocean. As with the alluvial fan, sediment carried by the water is deposited as the water slows down. Over time this creates an underwater fan. Deltas are triangular-shaped -- similar to the Greek letter delta -- and consist of gravel, sand, silt or clay. Examples of deltas are seen where the Mississippi River enters the Gulf of Mexico and where the Nile River in Egypt enters the Mediterranean Sea.

    Glaciers

    • Fan-shaped structures also form around glaciers. An expanded foot is a mass of ice shaped like a fan that occurs when a glacier extends beyond its valley walls onto a lower area at the bottom of a mountain. Also connected with glaciers, but consisting of sediment, an outwash fan is deposited at the front edge of a glacier by melted ice carrying sediment.

    Sand and Rock Debris

    • Sand glaciers are fan-shaped plains that form when sand blows up the side of a hill or mountain and spreads out on the opposite side. In this case wind -- not water -- carries the sediment. Likewise, colluvial fans do not involve the flow of water. Instead, gravity pulls sediment down a slope where it collects at the bottom in a fan-shaped deposit. Colluvial deposits are sometimes associated with alluvial deposits, which can be carried by water down the same slope.


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