Pediment (geology)
A pediment is a gently inclined erosional surface carved into bedrock. It is thinly covered with fluvial gravel that has developed at the foot of mountains. It develops when running water erodes most of the mass of the mountain. It is typically a concave surface gently sloping away from mountainous desert areas.[1]
Processes responsible for carving pediments
- "The removal of thin layers of surface material more or less evenly from an extensive area of gently sloping land, by broad continuous sheets of running water rather than by stream flowing in well defined channels"[3]
- Rillwash or rill erosion-
- "The development fo numerous minute closely spaced channels resulting from the uneven removal of surface soil by running water that is concentrate in streamlets of sufficient discharge and velocity to generate cutting power"[3]
- Mountain-front retreating by weathering
History
In 1877 Grove Karl Gilbert first observed pediments in the Henry Mountains in Utah. He described the formation as "hills of planation cut across the upturned edges of tilted beds". Gilbert believed the origin of pediments in the Henry Mountains are due to stream plantation and active erosion of deserts. This theory was advocated by Paige (1912), Blackwelder (1931), and Johnson 1932. Johnson came up with three zones of pediments.[1]
Zones of formation
Three formational zones are recognized:[1]
- An inner most zone of mountainous uplands that have near vertical erosion
- An intermediate zone or degradation zone which is the pediment beyond the mountain front.
- An outer zone or aggradation zone which extends beyond the pediment and is a zone of deposition.
References
- ^ a b c Easterbrook, Don J. (1999) Surface Processes and Landforms, New Jersey, Prentice Hall
- ^ Johnson, Douglas (1932) Rock Planes of Arid Regions, Geographical Review, Vol. 22, No. 4 (Oct., 1932), pp. 656–665
- ^ a b Wilson, William E. (editor) (1998) Glossary of Hydrology, American Geological Institute