Pediment (geology)

Pediment surface at base of Book Cliffs, Utah

A pediment, also known as a concave slope or waning slope,[1] is a very gently sloping (0.5°–7°) inclined bedrock surface.[2] It is typically a concave surface sloping down from the base of a steeper retreating desert cliff, escarpment,[3] or surrounding a monadnock or inselberg,[4][5] but may persist after the higher terrain has eroded away.[6]

Pediments are erosional surfaces. A pediment develops when sheets of running water (sheet floods) wash over it in intense rainfall events.[3] It may be thinly covered with fluvial gravel that has washed over it from the foot of mountains produced by cliff retreat erosion.[5]

A pediment is not to be confused with a bajada, which is a merged group of alluvial fans. Bajadas also slope gently from an escarpment, but are composed of material eroded from canyons in the escarpment and redeposited on the bajada, rather than of bedrock with a thin veneer of gravel.[6]

  1. ^ Allaby, Michael, ed. (2013). "Pediment". A dictionary of geology and earth sciences (Fourth ed.). Oxford University Press. ISBN 9780199653065.
  2. ^ Thornbury, William D. (1969). Principles of geomorphology (2nd ed.). New Delhi: CBS Publishers (2002 republication). pp. 271–272. ISBN 8123908113.
  3. ^ a b Marshak, Stephen (2009). Essentials of geology (3rd ed.). New York: W.W. Norton. p. 464. ISBN 978-0393932386.
  4. ^ Burbank, Douglas West; Anderson, Robert S. (2001). Tectonic geomorphology. Malden, Mass.: Blackwell Science. p. 28. ISBN 0632043865.
  5. ^ a b Easterbrook, Don J. (1999). Surface processes and landforms (2nd ed.). Upper Saddle River, N.J.: Prentice Hall. ISBN 0138609586.
  6. ^ a b Encyclopædia Britannica, Pediment