Concept

Pénéplaine

In geomorphology and geology, a peneplain is a low-relief plain formed by protracted erosion. This is the definition in the broadest of terms, albeit with frequency the usage of peneplain is meant to imply the representation of a near-final (or penultimate) stage of fluvial erosion during times of extended tectonic stability. Peneplains are sometimes associated with the cycle of erosion theory of William Morris Davis, but Davis and other workers have also used the term in a purely descriptive manner without any theory or particular genesis attached. The existence of some peneplains, and peneplanation as a process in nature, is not without controversy, due to a lack of contemporary examples and uncertainty in identifying relic examples. By some definitions, peneplains grade down to a base level represented by sea level, yet in other definitions such a condition is ignored. Geomorphologist Karna Lidmar-Bergström and co-workers consider the base level criterion crucial and above the precise mechanism of formation of peneplains, including this way some pediplains among peneplains. While peneplains are usually assumed to form near sea level it has also been posited that peneplains can form at height if extensive sedimentation raises the local base level sufficiently or if river networks are continuously obstructed by tectonic deformation. The peneplains of the Pyrenees and Tibetan Plateau may exemplify these two cases respectively. A common misconception about peneplains is that they ought to be so plain they are featureless. In fact, some peneplains may be hilly as they reflect irregular deep weathering, forming a plain grading to a base level only at a grand-scale. At the grand-scale peneplains are characterized by appearing to be sculpted in rock with disregard of rock structure and lithology, but in detail, their shape is structurally controlled, for example, drainage divides in peneplain can follow more resistant rock. In the view of Davis large streams do became insensitive to lithology and structure, which they were not during the valley phase of erosion cycle.

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Concepts associés (10)
Inselberg
thumb|Spitzkoppe, Namibie : inselberg et pédiment. Un inselberg ou monadnock est un relief (colline ou petit massif) isolé qui domine significativement une plaine ou un plateau subhorizontal (glacis d'érosion de type pédiment accumulé à son pied). Selon le Dictionnaire de la géographie de Pierre George (1970), il s'agit, brièvement, d'un relief résiduel rocheux, escarpé ; Pierre Birot les décrira ensuite comme des montagnes miniatures créées par l'érosion. Le terme inselberg provient de l'allemand berg et insel signifiant « montagne-île ».
Cycle of erosion
The geographic cycle, or cycle of erosion, is an idealized model that explains the development of relief in landscapes. The model starts with the erosion that follows uplift of land above a base level and ends, if conditions allow, in the formation of a peneplain. Landscapes that show evidence of more than one cycle of erosion are termed "polycyclical". The cycle of erosion and some of its associated concepts have, despite their popularity, been a subject of much criticism.
Surface d'aplanissement
vignette|upright=1.2|Vue des hautes terres kazakhes, qui sont une surface d'aplanissement tectonique (issue d'une surrection). La zone à l'arrière-plan ne présente quasiment plus de reliefs (pénéplaination). Les hautes terres kazakhes sont généralement référencées comme une pénéplaine. En géologie et géomorphologie, une surface d'aplanissement est une grande surface aplanie sur laquelle peuvent subsister quelques inselbergs. Les processus à l'origine de la formation des surfaces d'aplanissement sont exogènes (principalement issues de l'érosion).
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