Peneplain Definition
The term "peneplain" refers to an area that resembles a plain. It is created by river and rain erosion, which continues until nearly all of the elevated sections are eroded; the most resistant rocks typically rise above the land's general level. When a peneplain is raised, it becomes a Plateau, which is then dissected by the river as they cycle through youth and old age.
Peneplain Meaning
A peneplain is a low-relief plain created by long-term erosion in geomorphology and geology. This is the broadest concept, though the term peneplain is often used to refer to a near-final (or penultimate) stage of fluvial erosion during periods of prolonged tectonic stability. Peneplains are often synonymous with William Morris Davis's period of erosion theory, but Davis and others have often used the concept in a strictly descriptive sense without any theory or specific genesis attached.
Owing to a lack of contemporary examples and difficulty in recognizing relic examples, the presence of certain peneplains and peneplanation as a natural process is not without controversy. Peneplains grade down to a base level represented by sea level in some meanings, but this condition is ignored in others. The base-level criterion is important, according to geomorphologist Karna Lidmar-Bergström and colleagues, and it is above the precise mechanism of peneplain formation, which includes some pediplains among peneplains.
Although peneplains are normally thought to form near sea level, it has been suggested that they can form at a higher elevation if substantial sedimentation increases the local base level enough or tectonic deformation continuously obstructs river networks. These two instances can be exemplified by the Pyrenees peneplains and the Tibetan Plateau, respectively.
A popular misconception about peneplains is that they should be featureless in appearance. In reality, some peneplains may be hilly due to erratic deep weathering, resulting in a plain that only grads to a base level on a grand scale.
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Peneplain Geography
Rivers, glaciers, and winds break off and carry away rock fragments from mountain and plateau surfaces. As a result, these landforms, mountains, and plateaus are gradually lowered, and their rough surfaces smoothed out to form nearly flat plains. PENEPLAINS are the name given to these plains.
Types of Peneplains
Landforms that are either alternatives to classical peneplains, a subset of peneplains, or partly overlap with the term are referred to by a variety of names. Last but not least, there are planation surfaces that may or may not be peneplains, and certain peneplains are not planation surfaces.
Green, Lidmar-Bergström, and coworkers propose the following classification scheme for peneplains in their 2013 paper:
Surfaces for Plantation
Pediplain
Inselberg plain
Etchplain
Hilly Relief
Etched hilly relief
Peneplains may have been formed by etchplanation during periods of humid climate and pediplanation during periods of arid and semi-arid climate, according to Rhodes Fairbridge and Charles Finkl. Since some peneplains grow over long periods of time, they are subject to a wide range of climatic influences. Marine abrasion and glacial erosion are also listed as processes that can help shape peneplains by the same authors. Epigene peneplains are also distinguishable from exhumed peneplains. Peneplains that have never been buried or covered by sedimentary rock are known as epigene peneplains. Peneplains that have been re-exposed after being buried in sediments are known as exhumed peneplains.
Preservation and Destruction of Peneplains
Peneplains that have been uplifted or that have been separated from their base level can be marked by an accumulation of sediments that have buried them. The peneplain is preserved by burial. A paleo surface or paleo plan is any exposed peneplain that has been separated from its base level. Renewed erosion is typical when a peneplain is uplifted.
In extreme aridity or under non-eroding cold-based glacier ice, uplifted peneplains may be preserved as fossil landforms. In shield regions, glacier erosion of peneplains is minimal. During the Quaternary, glacier erosion averaged tens of meters in the Fennoscandian Shield, but it was not uniformly distributed. A long "preparation time" of weathering under non-glacial conditions may be required for glacier erosion to be successful in shields.
Peneplain surfaces exposed to subtropical and tropical climates for an extended period can be silicified, which can shield them from erosion.
FAQs on Peneplain
1. What is a peneplain in simple terms?
A peneplain is a large, gently undulating, low-relief plain. Imagine a mountainous or hilly landscape being worn down by rivers and streams over millions of years until it becomes almost flat. This near-featureless surface, formed close to the base level (usually sea level), is called a peneplain. The term literally means "almost a plain".
2. What is the process that leads to the formation of a peneplain?
A peneplain is formed through a long and continuous process of erosion, primarily by rivers, known as fluvial erosion. This is the end stage of the 'Geographic Cycle' or 'Cycle of Erosion' theory. The process involves:
- Weathering: Rocks on the surface are broken down into smaller pieces.
- Erosion: Rivers and streams carry away the weathered material.
- Down-wasting: The landscape is gradually lowered as the highlands and hills are eroded away, reducing the overall relief.
Over geological time, this continuous action wears the land down to a nearly flat surface.
3. How is a peneplain different from a pediplain?
While both are extensive plains of low relief, they are formed by different processes and in different climates. The main differences are:
- Formation Process: A peneplain is formed by river erosion (down-wasting) in humid regions. A pediplain is formed by the retreat of steep slopes and escarpments (back-wasting) in arid or semi-arid climates.
- Climate: Peneplains are associated with wet, humid climates, whereas pediplains are characteristic of dry, desert-like environments.
- Residual Hills: The hills left on a peneplain (monadnocks) are usually gently sloped, while those on a pediplain (inselbergs) are often steep and sharp.
4. What is a monadnock and how does it relate to a peneplain?
A monadnock is an isolated hill or small mountain of hard, resistant rock that stands prominently above a peneplain. It is a remnant of the original, higher landscape that was not eroded away because its rock was much tougher than the surrounding rock. Think of it as a stubborn piece of the old landform that survived the long process of erosion that flattened everything else around it.
5. Can you give some real-world examples of peneplains?
Perfect peneplains are rare because the Earth's crust is always moving, but several regions are considered classic examples of ancient peneplains that have since been uplifted. These include the Chota Nagpur Plateau in India, parts of the Canadian Shield near Hudson Bay, and the West Siberian Plain. These areas showcase the vast, low-relief landscapes characteristic of a peneplain.
