peneplain

[pene-, almost (from Latin paene) + PLAIN.]

(PEE-nuh-playn, pee-nuh-PLAYN)

noun
An area of nearly flat, featureless land formed by a long period of erosion. [From pene- (almost), from Latin paene + plain, from Latin planus

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Literally almost-a-plain, a plain scarcely rising above sea level at the coast, but rising gradually inland towards the occasional residual hills known as monadnocks. A peneplain is a low-lying erosion surface, but most existing peneplains are very old, and have been uplifted and dissected. Peneplanation is the wearing away of the entire landscape, so that the planation surface evolves over all sections at all times, whereas in pediplanation the scarps are subject to progressive retreat.

The central part of the Libyan desert has been described as a ‘desert peneplain’; the oldest and most enduring part of the desert, where arid processes are complete.

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Canisteo River Valley from Pinnacle State Park, New York. The distant peaks at the same elevation represent the remnants of a peneplain that was uplifted to form the Allegheny Plateau, which is a dissected plateau in southwestern New York. In this area, the sharp relief that is seen on some of the Allegheny Plateau has been rounded by glaciation.

A peneplain is the final stage in fluvial or stream erosion.

After the streams in an area have reached base level, lateral erosion is dominant - as the streams erode the highland areas between them. Finally, the upland is almost gone: the stream floodplains merge in an area of very low to no topographic relief. The resulting flat plain is the ultimate stage in the cycle of erosion or geographical cycle.

The streams within a peneplained region show extensive meandering and braiding. If the area is subsequently uplifted due to adjacent orogenic processes, without internal deformation within the peneplain, the streams will again begin downward erosion - creating incised meanders, water gaps, and other unique geomorphic features.

A peneplain can be mistaken for a depositional plain. However, the rocks beneath a peneplain have been folded and tilted by tectonic forces, while the rocks beneath a depositional plain lie in horizontal layers.

The peneplain concept was developed early in the 1900s by the geomorphologists, William Morris Davis and Walther Penck.

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