Pediments and Pediplains: Erosional Landforms
Landscape evolution in deserts is primarily concerned with the formation and extension of pediments. Gently inclined rocky floors close to the mountains at their foot with or without a thin cover of debris are called pediments. Such rocky floors form through the erosion of mountain front through a combination of lateral erosion by streams and sheet flooding.
A pediment is underlain by bedrock that is typically covered by a thin, discontinuous veneer of soil and alluvium derived from upland areas. Pediplains are formed at the end of major tectonic cycles during the transition from the orogenic stage of development of the earth’s crust to the platform stage.
Erosion starts along the steep margins of the landmass or the steep sides of the tectonically controlled steep incision feature over the landmass. Once, pediments are formed with a steep wash slope followed by the cliff or free face above it, the steep wash slope and free face retreat backward. This method of erosion is termed as a parallel retreat of slopes through backwashing. So, through parallel retreat of slopes, the pediments extend backward at the expense of mountain front, and gradually, the mountain gets reduced leaving an inselberg which is a remnant of the mountain. That’s how the high relief in desert areas is reduced to low featureless plains called pediplains.