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Pediplain
In geology and geomorphology a pediplain (from the Latin ''pes'', genitive case ''pedis'', meaning "foot") is an extensive plain formed by the coalescence of pediments. The processes through which pediplains forms is known as pediplanation. The concepts of pediplain and pediplanation were first developed by geologist Lester Charles King in his 1942 book ''South African Scenery''. The concept gained notoriety as it was juxtaposed to peneplanation. The coalesced pediments of the pediplains may form a series of very gentle concave slopes. Pediplains main difference to W. M. Davis’ peneplains is in the history and processes behind, and less so in the final shape. Perhaps the most notable difference in form that may be present is that of residual hills which in Davis’ peneplains are to have gentle slopes while in pediplains they ought to have the same steepness as the slopes in the early stages of erosion leading to pediplanation. Pediplanation is linked to scarp retreat in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Peneplain
390px, Sketch of a hypothetical peneplain formation after an orogeny. 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-Bergst ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pediment (geology)
A pediment, also known as a concave slope or waning slope, is a very gently sloping (0.5°-7°) inclined bedrock surface. It is typically a concave surface sloping down from the base of a steeper retreating desert cliff, escarpment, or surrounding a monadnock or inselberg, but may persist after the higher terrain has eroded away. Pediments are erosional surfaces. A pediment develops when sheets of running water ( sheet floods) wash over it in intense rainfall events. It may be thinly covered with fluvial gravel that has washed over it from the foot of mountains produced by cliff retreat erosion. A pediment is not to be confused with a bajada, which is a merged group of alluvial fans. Bajadas also slope gently from an escarpment, but are composed of material eroded from canyons in the escarpment and redeposited on the bajada, rather than of bedrock with a thin veneer of gravel. Description Pediments were originally recognized as the upper part of smoothly sloping (0.5°-7°) co ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Planation Surfaces
In geology and geomorphology a planation surface is a large-scale surface that is almost flat with the possible exception of some residual hills. The processes that form planation surfaces are labelled collectively planation and are exogenic (chiefly erosion). Planation surfaces are planated regardless of bedrock structures. On Earth, they constitute some of the most common landscapes. Geological maps indicate that planation surfaces may comprise 65% of the landscapes on Saturn's largest moon, Titan, which hosts a hydrological cycle of liquid methane. Peneplains and pediplains are types of planation surfaces planated respectively by "peneplanation" and "pediplanation". In addition to these there are planation surfaces proposed to be formed by cryoplanation, marine processes, areal glacial erosion and salt weathering. The term ''planation surface'' is often preferred over others because some more specific planation surface types and processes remain controversial. Etchplains are ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lester Charles King
Lester Charles King (1907–1989) was an English geologist and geomorphologist known for his theories on scarp retreat. He offered a very different view of the origin of continental landscaping than that of William Morris Davis. Studying at university in New Zealand King was a disciple of Charles Cotton who was heavily influenced by Davis. While King's ideas were an attempt at refuting Davis' cycle of erosion they were themselves of cyclical nature and contributed to what Cliff Ollier has called "Davis bashing" — the ridicule of cyclical theories in geomorphology, in particular Davis' ones. Critics did however not propose alternative models. For him, the weathering of physical factors in arid areas causes the erosion of the hills, the deposition of the weathered material (pediments) and the deposition of these material in lower altitudes, contributing to the formation of the pediplain. He was also an early proponent of continental drift Continental drift is the hypothesis ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hillslope Evolution
Hillslope evolution is the changes in the erosion rates, erosion styles and form of slopes of hills and mountains over time. Conceptual models During most of the 20th century three models of hillslope evolution were widely diffused: slope decline, slope replacement and parallel slope retreat. Until the 1950s models of hillslope form evolution were central in geomorphology. The modern understanding is that the evolution of slopes is much more complex than the classical models of decline, replacement and retreat imply. Slope decline Slope decline was proposed by William Morris Davis in his cycle of erosion theory. It consists of a gradual decrease in slope angle as stream incision slows down. This is accompaigned as slopes becomes more gentle they accumulate with fine-grained regolith stemming from weathering. Slope replacement Slope replacement was first proposed by Walther Penck challenging Davis' ideas on slope development. Slope replacement describes an evolution of slopes that ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cryoplanation
In geomorphology, cryoplanation or is a term used to both describe and explain the formation of plains, terraces and pediments in periglacial environments. Uncertainty surrounds the term, and the effectiveness of the cryoplanation process is held to be limited meaning it can only produce small terraces. Instead, many of so-called cryoplanation terraces are likely an expression of the underlying lithology and rock structure rather than being unique products of cold-climate processes. Cryoplanation can be seen as a variant of pediplanation that is restricted to cold climates. All the cryoplanation surfaces that exist at present date to the Quaternary. History of the concept The existence of flat bedrock surfaces in the mountains of Siberia was noted in the 1930s. Soviet scientists S.G. Boch and I.I. Krasnov first proposed a cyclical model for the formation these surfaces in 1943. This model influenced central and western European geomorphologists. Carl Troll, writing in German ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Etchplanation
An etchplain is a plain where the bedrock has been subject to considerable "etching" or subsurface weathering. Etchplanation is the process forming etchplains. Contrary to what the name might suggest, etchplains are seldom completely flat and usually display some relief, as weathering of the bedrock does not advance uniformly. This means that weathering is unrelated to the flatness which might be derivative of various other processes of planation including peneplanation and pediplanation. Erosion of etchplains can result in the exposure of inselbergs such as bornhardt and tors. Generally the topography exposed at a stripped etchplain, that is an etch surface, after erosion of regolith is one with many irregularities as result of structurally defined areas of rock strength. A distinction can be made between etchplains and etch surfaces as the latter may or may not be flat and can represent the landform arising from the stripping of an etchplain. As climate changes, arid and s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arid
A region is arid when it severely lacks available water, to the extent of hindering or preventing the growth and development of plant and animal life. Regions with arid climates tend to lack vegetation and are called xeric or desertic. Most arid climates straddle the Equator; these regions include parts of Africa, Asia, South America, North America, and Australia. Change over time The distribution of aridity at any time is largely the result of the general circulation of the atmosphere. The latter does change significantly over time through climate change. For example, temperature increase by 1.5–2.1 percent across the Nile Basin over the next 30–40 years could change the region from semi-arid to arid, significantly reducing the land usable for agriculture. In addition, changes in land use can increase demands on soil water and thereby increase aridity. See also * Arid Forest Research Institute * Aridity index * Desert climate * Desiccation tolerance * Drou ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Zeitschrift Für Geomorphologie
The ''Zeitschrift für Geomorphologie'' is a peer-reviewed scientific journal about geomorphology. The journal is indexed in Science Citation Index, GeoRef __NOTOC__ The GeoRef database is a bibliographic database that indexes scientific literature in the geosciences, including geology. Coverage ranges from 1666 to the present for North American literature, and 1933 to the present for the rest of t ..., Geodok and Scopus. It is published by E. Schweizerbart. External links * Earth and atmospheric sciences journals Multilingual journals Geomorphology journals E. Schweizerbart academic journals {{Geomorphology-journal-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
South Sudan
South Sudan (; din, Paguot Thudän), officially the Republic of South Sudan ( din, Paankɔc Cuëny Thudän), is a landlocked country in East Africa. It is bordered by Ethiopia, Sudan, Central African Republic, Democratic Republic of the Congo, Uganda and Kenya. Its population was estimated as 12,778,250 in 2019. Juba is the capital and largest city. It gained independence from Sudan on 9 July 2011, making it the most recent sovereign state or country with widespread recognition as of 2022. It includes the vast swamp region of the Sudd, formed by the White Nile and known locally as the '' Bahr al Jabal'', meaning "Mountain River". Sudan was occupied by Egypt under the Muhammad Ali dynasty and was governed as an Anglo-Egyptian condominium until Sudanese independence in 1956. Following the First Sudanese Civil War, the Southern Sudan Autonomous Region was formed in 1972 and lasted until 1983. A second Sudanese civil war soon broke out in 1983 and ended in 2005 w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
The Journal Of Geology
''The Journal of Geology'' publishes research on geology, geophysics, geochemistry, sedimentology, geomorphology, petrology, plate tectonics, volcanology, structural geology, mineralogy, and planetary sciences. Its content ranges from planetary evolution to computer modeling of fossil development, making it relevant to geologists as well as other researchers working in the Earth or planetary sciences. It was established in 1893 by Thomas Chrowder Chamberlin Thomas Chrowder Chamberlin (; September 25, 1843 – November 15, 1928) was an American geologist and educator. In 1893 he founded the '' Journal of Geology'', of which he was editor for many years. Biography Chamberlin was born September 25, 18 .... References External links * English-language journals Bimonthly journals University of Chicago Press academic journals Publications established in 1893 Geology journals {{geology-journal-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Semi-arid
A semi-arid climate, semi-desert climate, or steppe climate is a dry climate sub-type. It is located on regions that receive precipitation below potential evapotranspiration, but not as low as a desert climate. There are different kinds of semi-arid climates, depending on variables such as temperature, and they give rise to different biomes. Defining attributes of semi-arid climates A more precise definition is given by the Köppen climate classification, which treats steppe climates (''BSk'' and ''BSh'') as intermediates between desert climates (BW) and humid climates (A, C, D) in ecological characteristics and agricultural potential. Semi-arid climates tend to support short, thorny or scrubby vegetation and are usually dominated by either grasses or shrubs as it usually can't support forests. To determine if a location has a semi-arid climate, the precipitation threshold must first be determined. The method used to find the precipitation threshold (in millimeters): *multiply ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
