Alluvial fan

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  • (archaeology) a cone-shaped deposit of sediments generally formed where a mountain stream discharges onto a level surface. Alluvial fan deposits are among the most common surficial sediments in mountainous terrain.
  • (geology)
  1. Land counterpart of a delta: an assemblage of sediments marking place where a stream moves from a steep gradient to a flatter gradient and suddenly loses transporting power. Typical of arid and semiarid climates but not confined to them.
    Source: Leet, L. Don. 1982. Physical Geology, 6th Edition. Englewood Cliffs, NJ: Prentice-Hall
  2. A low, outspread, gently sloping mass of loose rock material, shaped in plan view like an open fan or a segment of a cone; deposited by a stream (esp. in a semiarid region) at the place where it issues from a narrow mountain valley upon a plain or broad valley, or where a tributary stream is near or at its junction with the main stream, or wherever a constriction in a valley abruptly ceases or the gradient of the stream suddenly decreases; it is steepest near the mouth of the valley where its apex points upstream, and it slopes gently and convexly outward with gradually decreasing gradient. CF: alluvial cone; bajada. Syn: fan; detrital fan; talus fan; dry delta. AGI
    Source: Dictionary of Mining, Mineral, and Related Terms

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