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Morphogenetic region-Geomorhology Chapter
- A morphogenetic region is a region where the dominant geomorphic processes, under certain climatic conditions, contribute to distinctive landscape characteristics that contrast with other regions formed under different climates. - The concept is based on the idea that each climate produces characteristic landforms through its influence on processes like weathering, erosion, and runoff. - Morphogenetic regions are defined by identifying major climatic/zoogeographical regions and the diagnostic landforms within them that reflect the dominant geomorphic processes operating under those particular climatic conditions.
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Introduction of morphogenetic regions and their characterization based on climatic influences according to key geomorphologists.
Discussion of landform variations across climates, emphasizing three themes of climatic geomorphology and the concept of diagnostic landforms.
Description of inselbergs as residual hills and pediments related to arid climates, discussing their climatic vs structural formation.
Analysis of how temperature, humidity, and vegetation impact denudational processes in different climatic zones.
Differentiation of humid tropical landforms from mid-latitude forms, with emphasis on temperature's effects on weathering and geomorphic processes.
Exploration of how climate affects vegetation and soils, and the subsequent impact on morphogenetic processes.
Classification of the globe into morphogenetic regions based on climatic and zoogeographical factors.
Presentation of the Köppen climate classification with detailed breakdown of climate types, focusing on temperature and precipitation.
Introduction to glaciers, types, and characteristics, emphasizing valley glaciers and their formation.
Wind's dual role as an erosive and depositional agent, examining how it shapes desert landscapes.
Description of glacio-fluvial landforms including eskers, kettle holes, and outwash plains, along with the concept of floodplains.
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- 1. Morphogenetic region A regionin which, under certain climatic conditions, the predominant geomorphic processes will contribute regional characteristics of landscape that contrast with those of other regions formed under different climatic conditions. The concepts of climatic geomorphology and morpho- climatic/morphogenetic landscapes and regions was enriched by the classical work of J. Budel (1948, 1982), L.C. Peltier (1950), C. Troll (1958), W.F. Tanner (1961), P. Birot (1968), D.R. Stoddart (1969), L. Wilson (1969, 1973), J. Tricart and A. Cailleux (19720 etc. They argue that the rate of operation of weathering and erosional processes, vegetation type, surface runoff, nature, and rate of erosion and mechanisms of landform genesis and development differ considerably from one climatic region to the other but it may be pointed out that they could not be able to present convincing evidences in support of
- 2. • Morphogenetic regions •The concept of morphogenetic/morphoclimatic regions is based on the basic concept of climatic geomorphology that ‘each geomorphic process produces its own characteristic assemblage of landforms, and each geomorphic process is the result of a particular climate’ and thus, each climatic type produces its own characteristic assemblage of distinctive landforms. According to Chorley et. Al. (1985) morphogenetic regions are large areal units within which distinctive associations of geomorphic processes (weathering, frost action, mass movements, fluvial action and wind action) are assumed to operate, tending towards a state of morphoclimatic equlibrium wherein regional landforms reflect regional climates.” • The following criteria for the determination and definition of morphogenetic regions- • A. Identification and classification of major morphogenetic regions on the basis of major climatic and zoogeographical regions. •
- 3. their arguments asyet. The concept of climatic geomorphology is based on the following three major themes (d.R. Stoddart, 1969)- 1. Landforms differ significantly in different climatic regions. 2. Spatial variations of landforms in different climatic regions are because of spatial variations in climatic parameters (tempt., humidity, precipt. etc.) and their influences on weathering, erosion and runoff. 3. Quaternary climatic changes could not obscure relationships between landforms and climates. In other words, there are certain diagnostic landforms which clearly demonstrate climate-landforms relationships. Diagnostic landforms: The advocates of climatic geomorphology have attempted to collect information about the characteristics of such landforms which may be regarded as diagnostic landforms to determine climate-landforms relationships.
- 4. Such typical diagnosticlandforms are regarded as representatives of a particular climate. Climatogenetic or climatically controlled landforms are identified and differentiated in two ways, (i) general observation of whole landscape of each climatic region (ii) identification of typical or distinctive landforms which represent the control of a particular climate. Such distinctive landforms are designated as ‘diagnostic landforms’. Inselbergs representing steep side residual hills are considered to be the representative landforms of hot and arid and semi-arid climates and the end product of arid cycle of erosion. But inselbergs are found in different parts of the world having different ‘climatic conditions’ from humid subtropical in Georgia, North America to humid tropical in the Guinea coastlands, south India, Brazil and to Desert areas in western North America, Mauretania, and South-west Africa. It is argued that inselbergs are structurally controlled rather than climatically controlled and most of the present inselbergs were formed before Quaternary epoch.
- 5. An inselberg isa residual relief feature--an isolated hill, ridge, or small mountain that rises abruptly, like an island, from a gently sloping or virtually level surrounding plain (inselberg is a German word meaning "island mountain").
- 6. • A toris a rock outcrop formed by weathering, usually found on or near the summit of a hill. In the South West of England, where the term originated, it is also a word used for the hills themselves – particularly the high points of Dartmoor in Devon and Bodmin Moor in Cornwall.
- 7. It may bepossible that inselbergs might have been formed when the climate was arid or semi-arid which might have changed after their formation. Pediments, characterised by low-angle rock-cut surfaces surrounding mountains, are considered to be the representative landforms of arid and semi-arid climates. Pediments are also found in a variety of climatic conditions e.g. tropical wet and dry climate, subtropical and temperate climate. Penck argue that pediments are structurally and tectonically controlled rather than climatically. King has opined that the process of pediplanation and pedimentation is universal and it occurs in all environmental conditions. It may be concluded that the aforesaid diagnostic landforms are older than Pleistocene climatic changes, so they are definitely not related to present climates where they are found. Geomorphic processes and climatic controls It is fact that different processes work different climatic
- 8. regions and withclimatic variations there is also variability in the nature and mode of influences of climatic parameters which affect denudational (weathering and erosional) processes.
- 9. • Temperature andhumidity have emerged as the most significant climatic parameters of the control of geomorphological processes in different climatic regions. High mean annual temperature and rainfall favour deep chemical weathering in humid tropics. • Besides, vegetation also plays important role in controlling geomorphic processes in tropical humid areas, because the combination of high mean annual temperature and rainfall favour dense vegetation even on steeper slopes with the result the processes of soil erosion, sheetwash and physical weathering are considerably slowed down. • Dense vegetation of humid tropics also reduces surface runoff because a sizeable portion of rainfall is intercepted by forest canopy and thus rainwater reaches the ground surface in the form of aerial streamlets through the leaves, twigs, branches and stems of trees and thus allows more infiltration.
- 12. • T. C.Chamberlin and R. T. Chamberlin (1910) differentiated landforms of humid tropics from those of the mid-latitude temperate landforms. Different rock types respond differently to the combinations of water and temperature in different climates. Limestones become chemically weak to weathering and erosion in hot and humid climate because chemical weathering becomes more active but these become resistant to chemical weathering in hot and arid climate because of scarcity of water and humidity. • Direct controls of climate • The different morphogenetic processes operate in different climatic variation. The mode and rate of operation of geomorphic processes also differ from one climatic region to the other. Besides weathering, climate also influences the mechanisms of transportation and deposition. • Temperature is a very significant climatic parameter which not only influences but also controls the mechanisms of different morphogenetic processes. It is known to all that
- 13. • Temperature variesconsiderably in different climatic regions. If temperature of a region is below freezing point during night but rises above freezing point during day time then there occurs diurnal freeze and thaw cycle which leads to alternate processes of contraction and expansion. The repetition of this mechanism causes frost weathering in periglacial climate ( solifluction) during transitional periods of summer and winter seasons. • Exfoliation… • Indirect climate controls • (Climate vegetation Morphogenetic processes) • Climate influences and controls morphogenetic processes indirectly through 1. vegetation and 2. soils. The world distribution of vegetation is azonal which is closely related to climate zones. Climate and soils are so intimately interrelated that influence each other. Vegetation determines pedogenesis while soils determine vegetation types which again depend on climate. Vegetation, in turn,
- 15. • In geology,solifluction, also known as soil fluction, is a type of mass wasting where waterlogged sediment moves slowly downslope, over impermeable material.
- 16. • Also influencesfloral characteristics. These interactions between climate, soils and vegetation, in turn, influence and control nature, type and mode of operation of different denudational processes. • The kinetic energy of rainfall (say raindrop) and its geomorphic significance is greatly controlled by interception capacity of vegetation. It may be pointed out that the areas devoid of vegetation (open areas) are directly affected by falling raindrops with maximum kinetic energy and causes splash erosion wherein loose particles are resettled on the ground surface which discourages infiltration of rainwater and favours increased surface runoff. On the other hand, densely vegetated areas mainly of forests are characterised by least splash erosion because of maximum interception of rainwater. There is maximum interception of rainwater in equatorial rainforests of humid tropics wherein ‘aerial streams’ become most effective.
- 17. • Climate vegetationSoil and Morphogenetic processes • It may be mentioned that climate influences vegetation and in turn vegetation influences soils and morphogenetic processes. It may be pointed out that it is not necessary that climate always influences morphogenetic processes via vegetation and soils. Thus, the following relationships between these variables may be identified 1. climate vegetation morphogenetic processes landforms • 2. climate soils morphogenetic processes landforms • 3. climate morphogenetic processes landforms
- 18. • Morphogenetic regions •The concept of morphogenetic/morphoclimatic regions is based on the basic concept of climatic geomorphology that ‘each geomorphic process produces its own characteristic assemblage of landforms, and each geomorphic process is the result of a particular climate’ and thus, each climatic type produces its own characteristic assemblage of distinctive landforms. According to Chorley et. Al. (1985) morphogenetic regions are large areal units within which distinctive associations of geomorphic processes (weathering, frost action, mass movements, fluvial action and wind action) are assumed to operate, tending towards a state of morphoclimatic equlibrium wherein regional landforms reflect regional climates.” • The following criteria for the determination and definition of morphogenetic regions- • A.Identification and classification of major morphogenetic regions on the basis of major climatic and zoogeographical regions. •
- 19. • B. Subdivisionof major morphogenetic region on the basis of present climatic, zoogeographical and paleoclimatic factors. • On the basis of these two criteria they divided the globe into 4 major morphogenetic regions and 9 sub-regions as follows: • 1. Cold zone morphogenetic regions • a. glacial zone –characterized by runoff in solid form e.g. glaciers • b. periglacial zone- characterized by runoff in liquid form- water during summer. • 2. Forested zone morphogenetic regions • a. Maritime zone: normal winter season, no significant frost action, more influence of Pleistocne glacial and periglacial relict features. • b. continental zone: winter severely cold, effects of Pleistocene and present frost most dominant.
- 20. • c. mediterraneanzone: dry summer, wet winter, insignificant effects of Quaternary periglacial relict feature. • 3. Semi-arid and Arid morphogenetic regions: • (A) on the basis of aridity • (a) stepe regions • (b) xerophytic region • (c) desert region • (B) on the basis of winter temperature • (a) middle latitude region • (b) subtropical region • (c) tropical region • 4. Humid Tropical morphogenetic regions • (a) savana region: dry and wet seasons, seasonal rainfall, moderate vegetation cover, enough overland flow, active chemical weathering during wet season. • (b) forest region: humid tropical region, rainfall throughout • The year, maximum vegetation cover, chemical and biological weathering most dominant.
- 22. The Köppen climateclassification is one of the most widely used climate classification systems. It was first published by Crimea German climatologist W. Köppen in 1884. • Köppen's scheme uses five basic types of climate: • A: humid tropical • B: dry • C: humid mesothermal • D: humid microthermal • E: polar/arctic • Taking into account temperature and precipitation, some 23 more- precise categories can be devised. • A-- tropical (coldest 18°C) --Af: moist, Am: monsoon; Aw: winter dry period • B-- no temperature limitation ; BS: steppe; BW: desert • C-- mesothermal (-3°C to 18°C); Cf: moist; precipitation distributed throughout year; Cw: winter dry period; Cs: summer dry period • D-- microthermal ( < -3°C to 18°C) ; Df: moist; precipitation distributed throughout year, Dw: winter dry period • E-- arctic (warmest < 10°C)
- 24. • Glaciers • Typesof Glaciers • An ice age is a period of time when much of earth's land is covered in glaciers. • A glacier is a thick ice mass that forms over hundreds of thousands of years.
- 25. • Valley Glaciers • ValleyGlaciers are ice masses that slowly advance down valleys that were originally occupied by streams. It is a stream with ice that flows between steep rock walls from a place near the top of a mountain valley.
- 26. • Horns • Hornsare sharp pyramid like peaks
- 30. Alluvial fans arefan-shaped deposits of water-transported material (alluvium). They typically form at the base of topographic features where there is a marked break in slope. Consequently, alluvial fans tend to be coarse-grained, especially at their mouths. At their edges, however, they can be relatively fine-grained.
- 31. • Most Desertstream dry up before they reach the ocean. • Interior drainage into basin produces: • - alluvial fans- a cone of debris
- 32. • Playa lakes-a flat area on the floor of an undrained desert basin that fills and becomes a lake after heavy rain. Bajada: Gently sloping depositional plain between pediments and playa is called bajada.
- 33. • Landscapes Shapedby Wind • Wind Erosion • Wind erodes in the desert 2 ways: • - deflation, is the lifting and removal of loose particles such as clay and silt. • - abrasion, happens when wind blown sand cuts and polishes exposed rock surfaces. • Wind Deposits • The wind can create landforms when it deposits its sediments especially in deserts and along coast. both layers of loess and sand dunes are landscape features deposited by wind. • Loess is windblown silt the blankets the landscape. • Unlike deposits of loess which form blanket-like layers over broad areas, winds commonly deposit sand in mound or ridges called dunes.
- 34. • Badlands occurwhere weak clays or shales are exposed to rapid erosion by running water in semiarid regions.
- 35. • Types ofSand Dunes • What form sand dunes assume depends on the wind direction and speed, how much sand is available, and the amount of vegetation. • Barchan dunes- solitary dunes chaped like crescent
- 36. • Wind Erosion •Wind can be effective agent of erosion anywhere that it is strong enough to act. Wind can erode by deflation and abrasion. • Deflation is the lowering of the land surface due to removal of fine-grained particles by the wind. Deflation concentrates the coarser grained particles at the surface, eventually resulting in a surface composed only of the coarser grained fragments that cannot be transported by the wind. Such a surface is called desert pavement.
- 37. • Glacio-fluvial landforms: •Eskers: Eskars are long, narrow and sinuous of sands and gravels and are situated in the middle of ground morains. • kettle holes description - This is a small hollow on the landscape. These are often filled with water (kettle lakes). • outwash plains description - These are vast fairly level areas located to the 'front' of a terminal moraine. explanation - As a glacier or ice sheet melted (ablated) then the meltwater carried deposits of gravel, sand ,silt and clay.
- 39. • Erosive activityat different stream gradient
- 40. • Floodplain: Floodplainsare simply the areas of land that river floods onto when they exceed bankfull discharge. Floodplains are created by the constant movement of meanders. Floodplains tend to be a lot wider in a river's lower course.