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84-567: The British Society for Geomorphology (BSG), incorporating the British Geomorphological Research Group (BGRG), is the professional organisation for British geomorphologists and provides a community and services for those involved in teaching or research in geomorphology, both in the UK and overseas. The society’s journal, Earth Surface Processes and Landforms is published by Wiley-Blackwell and online access

168-424: A certain proportion of its mass below the surface of the water. If snow falls to the top of the iceberg, the iceberg will sink lower in the water. If a layer of ice melts off the top of the iceberg, the remaining iceberg will rise. Similarly, Earth's lithosphere "floats" in the asthenosphere. When continents collide, the continental crust may thicken at their edges in the collision. It is also very common for one of

252-425: A change in crust loading) provide information on the viscosity of the upper mantle. The basis of the model is Pascal's law , and particularly its consequence that, within a fluid in static equilibrium, the hydrostatic pressure is the same on every point at the same elevation (surface of hydrostatic compensation): h 1 ⋅ρ 1 = h 2 ⋅ρ 2 = h 3 ⋅ρ 3 = ... h n ⋅ρ n For the simplified picture shown,

336-535: A characteristic wave number As the rigid layer becomes weaker, κ {\displaystyle \kappa } approaches infinity, and the behavior approaches the pure hydrostatic balance of the Airy-Heiskanen hypothesis. The depth of compensation (also known as the compensation level , compensation depth , or level of compensation ) is the depth below which the pressure is identical across any horizontal surface. In stable regions, it lies in

420-414: A concept of physiographic regions while a conflicting trend among geographers was to equate physiography with "pure morphology", separated from its geological heritage. In the period following World War II, the emergence of process, climatic, and quantitative studies led to a preference by many earth scientists for the term "geomorphology" in order to suggest an analytical approach to landscapes rather than

504-491: A decline in the popularity of climatic geomorphology in the late 20th century. Stoddart criticized climatic geomorphology for applying supposedly "trivial" methodologies in establishing landform differences between morphoclimatic zones, being linked to Davisian geomorphology and by allegedly neglecting the fact that physical laws governing processes are the same across the globe. In addition some conceptions of climatic geomorphology, like that which holds that chemical weathering

588-438: A descriptive one. During the age of New Imperialism in the late 19th century European explorers and scientists traveled across the globe bringing descriptions of landscapes and landforms. As geographical knowledge increased over time these observations were systematized in a search for regional patterns. Climate emerged thus as prime factor for explaining landform distribution at a grand scale. The rise of climatic geomorphology

672-574: A fictional dialogue where the immortal Magu explained that the territory of the East China Sea was once a land filled with mulberry trees . The term geomorphology seems to have been first used by Laumann in an 1858 work written in German. Keith Tinkler has suggested that the word came into general use in English, German and French after John Wesley Powell and W. J. McGee used it during

756-533: A local hydrostatic balance. A third hypothesis, lithospheric flexure , takes into account the rigidity of the Earth's outer shell, the lithosphere . Lithospheric flexure was first invoked in the late 19th century to explain the shorelines uplifted in Scandinavia following the melting of continental glaciers at the end of the last glaciation . It was likewise used by American geologist G. K. Gilbert to explain

840-435: A mountain belt to promote further erosion as mass is removed from the chain and the belt uplifts. Long-term plate tectonic dynamics give rise to orogenic belts , large mountain chains with typical lifetimes of many tens of millions of years, which form focal points for high rates of fluvial and hillslope processes and thus long-term sediment production. Features of deeper mantle dynamics such as plumes and delamination of

924-490: A region, the land may rise to compensate. Therefore, as a mountain range is eroded, the (reduced) range rebounds upwards (to a certain extent) to be eroded further. Some of the rock strata now visible at the ground surface may have spent much of their history at great depths below the surface buried under other strata, to be eventually exposed as those other strata eroded away and the lower layers rebounded upwards. An analogy may be made with an iceberg , which always floats with

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1008-447: A short period of time, making them extremely important entities in the high latitudes and meaning that they set the conditions in the headwaters of mountain-born streams; glaciology therefore is important in geomorphology. Isostasy Isostasy (Greek ísos 'equal', stásis 'standstill') or isostatic equilibrium is the state of gravitational equilibrium between Earth 's crust (or lithosphere ) and mantle such that

1092-490: A valley causes abrasion and plucking of the underlying rock . Abrasion produces fine sediment, termed glacial flour . The debris transported by the glacier, when the glacier recedes, is termed a moraine . Glacial erosion is responsible for U-shaped valleys, as opposed to the V-shaped valleys of fluvial origin. The way glacial processes interact with other landscape elements, particularly hillslope and fluvial processes,

1176-607: A very brief outline of some of the major figures and events in its development. The study of landforms and the evolution of the Earth's surface can be dated back to scholars of Classical Greece . In the 5th century BC, Greek historian Herodotus argued from observations of soils that the Nile delta was actively growing into the Mediterranean Sea , and estimated its age. In the 4th century BC, Greek philosopher Aristotle speculated that due to sediment transport into

1260-768: Is a forum for emerging approaches to solve key challenges throughout pure and applied Geomorphology. The Annual Conference for 2025 will be held at the University of Leeds in September. Earth Surface Processes and Landforms is the flagship international journal of the BSG, edited by Stuart Lane (Managing Editor) and five Associate Editors. The Journal publishes original research papers, Earth Surface Exchanges (shorter articles, commentaries, reviews and discussion papers) for rapid publication, technical communications and book reviews across all branches of geomorphology. In July 2017,

1344-603: Is an important aspect of Plio-Pleistocene landscape evolution and its sedimentary record in many high mountain environments. Environments that have been relatively recently glaciated but are no longer may still show elevated landscape change rates compared to those that have never been glaciated. Nonglacial geomorphic processes which nevertheless have been conditioned by past glaciation are termed paraglacial processes. This concept contrasts with periglacial processes, which are directly driven by formation or melting of ice or frost. Soil , regolith , and rock move downslope under

1428-785: Is available free to members. The society is affiliated with the Royal Geographical Society as an affiliated research group and with the Geological Society of London as a specialist group. The mission of the British Society for Geomorphology is to support scientific excellence in geomorphology through: The Annual Conference of the British Society for Geomorphology (BSG) is an international Open Conference. This Annual Meeting stimulates debate on new developments and advances in Geomorphology, and

1512-528: Is defined as the Bouger anomaly minus the gravity anomaly due to the subsurface compensation, and is a measure of the local departure from isostatic equilibrium. At the center of a level plateau, it is approximately equal to the free air anomaly . Models such as deep dynamic isostasy (DDI) include such viscous forces and are applicable to a dynamic mantle and lithosphere. Measurements of the rate of isostatic rebound (the return to isostatic equilibrium following

1596-699: Is extremely important in sedimentology . Weathering is the chemical and physical disruption of earth materials in place on exposure to atmospheric or near surface agents, and is typically studied by soil scientists and environmental chemists , but is an essential component of geomorphology because it is what provides the material that can be moved in the first place. Civil and environmental engineers are concerned with erosion and sediment transport, especially related to canals , slope stability (and natural hazards ), water quality , coastal environmental management, transport of contaminants, and stream restoration . Glaciers can cause extensive erosion and deposition in

1680-611: Is more rapid in tropical climates than in cold climates proved to not be straightforwardly true. Geomorphology was started to be put on a solid quantitative footing in the middle of the 20th century. Following the early work of Grove Karl Gilbert around the turn of the 20th century, a group of mainly American natural scientists, geologists and hydraulic engineers including William Walden Rubey , Ralph Alger Bagnold , Hans Albert Einstein , Frank Ahnert , John Hack , Luna Leopold , A. Shields , Thomas Maddock , Arthur Strahler , Stanley Schumm , and Ronald Shreve began to research

1764-444: Is probably of profound importance for the terrestrial geomorphic system as a whole. Biology can influence very many geomorphic processes, ranging from biogeochemical processes controlling chemical weathering , to the influence of mechanical processes like burrowing and tree throw on soil development, to even controlling global erosion rates through modulation of climate through carbon dioxide balance. Terrestrial landscapes in which

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1848-415: Is since the 1990s no longer accepted by mainstream scholarship as a basis for geomorphological studies. Albeit having its importance diminished, climatic geomorphology continues to exist as field of study producing relevant research. More recently concerns over global warming have led to a renewed interest in the field. Despite considerable criticism, the cycle of erosion model has remained part of

1932-445: Is the acceleration due to gravity, and P ( x ) {\displaystyle P(x)} is the load on the ocean crust. The parameter D is the flexural rigidity , defined as where E is Young's modulus , σ {\displaystyle \sigma } is Poisson's ratio , and T c {\displaystyle T_{c}} is the thickness of the lithosphere. Solutions to this equation have

2016-476: The Baltic Sea and Hudson Bay . As the ice retreats, the load on the lithosphere and asthenosphere is reduced and they rebound back towards their equilibrium levels. In this way, it is possible to find former sea cliffs and associated wave-cut platforms hundreds of metres above present-day sea level . The rebound movements are so slow that the uplift caused by the ending of the last glacial period

2100-597: The Bulletin of the Geological Society of America , and received only few citations prior to 2000 (they are examples of "sleeping beauties" ) when a marked increase in quantitative geomorphology research occurred. Quantitative geomorphology can involve fluid dynamics and solid mechanics , geomorphometry , laboratory studies, field measurements, theoretical work, and full landscape evolution modeling . These approaches are used to understand weathering and

2184-534: The Hawaiian Islands . Although Earth is a dynamic system that responds to loads in many different ways, isostasy describes the important limiting case in which crust and mantle are in static equilibrium . Certain areas (such as the Himalayas and other convergent margins) are not in isostatic equilibrium and are not well described by isostatic models. The general term isostasy was coined in 1882 by

2268-401: The crust "floats" at an elevation that depends on its thickness and density. This concept is invoked to explain how different topographic heights can exist at Earth's surface. Although originally defined in terms of continental crust and mantle, it has subsequently been interpreted in terms of lithosphere and asthenosphere , particularly with respect to oceanic island volcanoes , such as

2352-520: The American geologist Clarence Dutton . In the 17th and 18th centuries, French geodesists (for example, Jean Picard ) attempted to determine the shape of the Earth (the geoid ) by measuring the length of a degree of latitude at different latitudes ( arc measurement ). A party working in Ecuador was aware that its plumb lines , used to determine the vertical direction, would be deflected by

2436-563: The British Geomorphological Research Group (BGRG). The first BGRG AGM was held on 1 October 1960. Morphological mapping schemes, emphasising slope, were the subject for discussion at early meetings of the BGRG. Time-consuming to undertake, such schemes produced information about form but not about the processes or the origin of land forms. These schemes evolved in the 1970s to produce geomorphological maps of

2520-667: The Earth illustrate this intersection of surface and subsurface action. Mountain belts are uplifted due to geologic processes. Denudation of these high uplifted regions produces sediment that is transported and deposited elsewhere within the landscape or off the coast. On progressively smaller scales, similar ideas apply, where individual landforms evolve in response to the balance of additive processes (uplift and deposition) and subtractive processes ( subsidence and erosion ). Often, these processes directly affect each other: ice sheets, water, and sediment are all loads that change topography through flexural isostasy . Topography can modify

2604-655: The Earth, biological processes such as burrowing or tree throw may play important roles in setting the rates of some hillslope processes. Both volcanic (eruptive) and plutonic (intrusive) igneous processes can have important impacts on geomorphology. The action of volcanoes tends to rejuvenize landscapes, covering the old land surface with lava and tephra , releasing pyroclastic material and forcing rivers through new paths. The cones built by eruptions also build substantial new topography, which can be acted upon by other surface processes. Plutonic rocks intruding then solidifying at depth can cause both uplift or subsidence of

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2688-530: The International Geological Conference of 1891. John Edward Marr in his The Scientific Study of Scenery considered his book as, 'an Introductory Treatise on Geomorphology, a subject which has sprung from the union of Geology and Geography'. An early popular geomorphic model was the geographical cycle or cycle of erosion model of broad-scale landscape evolution developed by William Morris Davis between 1884 and 1899. It

2772-560: The Pratt hypothesis as overlying regions of unusually low density in the upper mantle. This reflects thermal expansion from the higher temperatures present under the ridges. In the Basin and Range Province of western North America, the isostatic anomaly is small except near the Pacific coast, indicating that the region is generally near isostatic equilibrium. However, the depth to the base of

2856-709: The UK. Several articles published in the Geographical Magazine in 1975 and 1976 explained the landform maps produced for all parts of Britain. In 1985 the BGRG celebrated its first twenty five years by hosting the first International Geomorphology Conference in Manchester which led to the formation of the International Association of Geomorphology. In 2000, 40 years of the BGRG were celebrated by returning to Sheffield. Of those 19 geomorphologists who, by their action, can be regarded as

2940-441: The availability of sediment itself and on the river's discharge . Rivers are also capable of eroding into rock and forming new sediment, both from their own beds and also by coupling to the surrounding hillslopes. In this way, rivers are thought of as setting the base level for large-scale landscape evolution in nonglacial environments. Rivers are key links in the connectivity of different landscape elements. As rivers flow across

3024-403: The balancing of lithospheric columns gives: where ρ m {\displaystyle \rho _{m}} is the density of the mantle (ca. 3,300 kg m ), ρ c {\displaystyle \rho _{c}} is the density of the crust (ca. 2,750 kg m ) and ρ w {\displaystyle \rho _{w}} is the density of

3108-539: The centuries. He inferred that the land was reshaped and formed by soil erosion of the mountains and by deposition of silt , after observing strange natural erosions of the Taihang Mountains and the Yandang Mountain near Wenzhou . Furthermore, he promoted the theory of gradual climate change over centuries of time once ancient petrified bamboos were found to be preserved underground in

3192-418: The crust does not strongly correlate with the height of the terrain. This provides evidence (via the Pratt hypothesis) that the upper mantle in this region is inhomogeneous, with significant lateral variations in density. The formation of ice sheets can cause Earth's surface to sink. Conversely, isostatic post-glacial rebound is observed in areas once covered by ice sheets that have now melted, such as around

3276-457: The cycle over. In the decades following Davis's development of this idea, many of those studying geomorphology sought to fit their findings into this framework, known today as "Davisian". Davis's ideas are of historical importance, but have been largely superseded today, mainly due to their lack of predictive power and qualitative nature. In the 1920s, Walther Penck developed an alternative model to Davis's. Penck thought that landform evolution

3360-448: The deep crust, but in active regions, it may lie below the base of the lithosphere. In the Pratt model, it is the depth below which all rock has the same density; above this depth, density is lower where topographic elevation is greater. When large amounts of sediment are deposited on a particular region, the immense weight of the new sediment may cause the crust below to sink. Similarly, when large amounts of material are eroded away from

3444-406: The deformation of the rigid crust. These elastic forces can transmit buoyant forces across a large region of deformation to a more concentrated load. Perfect isostatic equilibrium is possible only if mantle material is in rest. However, thermal convection is present in the mantle. This introduces viscous forces that are not accounted for the static theory of isostacy. The isostatic anomaly or IA

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3528-411: The depth of the mountain belt roots (b 1 ) is calculated as follows: where ρ m {\displaystyle \rho _{m}} is the density of the mantle (ca. 3,300 kg m ) and ρ c {\displaystyle \rho _{c}} is the density of the crust (ca. 2,750 kg m ). Thus, generally: In the case of negative topography (a marine basin),

3612-571: The dry, northern climate zone of Yanzhou , which is now modern day Yan'an , Shaanxi province. Previous Chinese authors also presented ideas about changing landforms. Scholar-official Du Yu (222–285) of the Western Jin dynasty predicted that two monumental stelae recording his achievements, one buried at the foot of a mountain and the other erected at the top, would eventually change their relative positions over time as would hills and valleys. Daoist alchemist Ge Hong (284–364) created

3696-413: The early 1900s, the study of regional-scale geomorphology was termed "physiography". Physiography later was considered to be a contraction of " physi cal" and "ge ography ", and therefore synonymous with physical geography , and the concept became embroiled in controversy surrounding the appropriate concerns of that discipline. Some geomorphologists held to a geological basis for physiography and emphasized

3780-495: The early 19th century, authors – especially in Europe – had tended to attribute the form of landscapes to local climate , and in particular to the specific effects of glaciation and periglacial processes. In contrast, both Davis and Penck were seeking to emphasize the importance of evolution of landscapes through time and the generality of the Earth's surface processes across different landscapes under different conditions. During

3864-430: The field of geomorphology encompasses a very wide range of different approaches and interests. Modern researchers aim to draw out quantitative "laws" that govern Earth surface processes, but equally, recognize the uniqueness of each landscape and environment in which these processes operate. Particularly important realizations in contemporary geomorphology include: According to Karna Lidmar-Bergström , regional geography

3948-403: The flexural rigidity of the lithosphere approaches zero. For example, the vertical displacement z of a region of ocean crust would be described by the differential equation where ρ m {\displaystyle \rho _{m}} and ρ w {\displaystyle \rho _{w}} are the densities of the aesthenosphere and ocean water, g

4032-590: The force of gravity via creep , slides , flows, topples, and falls. Such mass wasting occurs on both terrestrial and submarine slopes, and has been observed on Earth , Mars , Venus , Titan and Iapetus . Ongoing hillslope processes can change the topology of the hillslope surface, which in turn can change the rates of those processes. Hillslopes that steepen up to certain critical thresholds are capable of shedding extremely large volumes of material very quickly, making hillslope processes an extremely important element of landscapes in tectonically active areas. On

4116-494: The form of landscape elements such as rivers and hillslopes by taking systematic, direct, quantitative measurements of aspects of them and investigating the scaling of these measurements. These methods began to allow prediction of the past and future behavior of landscapes from present observations, and were later to develop into the modern trend of a highly quantitative approach to geomorphic problems. Many groundbreaking and widely cited early geomorphology studies appeared in

4200-456: The formation of deep sedimentary basins where the surface of the Earth drops and is filled with material eroded from other parts of the landscape. The Earth's surface and its topography therefore are an intersection of climatic , hydrologic , and biologic action with geologic processes, or alternatively stated, the intersection of the Earth's lithosphere with its hydrosphere , atmosphere , and biosphere . The broad-scale topographies of

4284-670: The formation of soils , sediment transport , landscape change, and the interactions between climate, tectonics, erosion, and deposition. In Sweden Filip Hjulström 's doctoral thesis, "The River Fyris" (1935), contained one of the first quantitative studies of geomorphological processes ever published. His students followed in the same vein, making quantitative studies of mass transport ( Anders Rapp ), fluvial transport ( Åke Sundborg ), delta deposition ( Valter Axelsson ), and coastal processes ( John O. Norrman ). This developed into "the Uppsala School of Physical Geography ". Today,

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4368-582: The founders of the BGRG, which now has an international membership of around 700, nine attended this 40th Anniversary Meeting. One of them, Tony Orme, presented the Frost Lecture. In 2006 the BGRG changed its name to British Society for Geomorphology (BSG). The new Constitution stated that the object of the Society shall be the advancement of the science of geomorphology, in research, in all levels of education, and in its practical application. Chairs of

4452-427: The geologic and atmospheric history of those planets but also extends geomorphological study of the Earth. Planetary geomorphologists often use Earth analogues to aid in their study of surfaces of other planets. Other than some notable exceptions in antiquity, geomorphology is a relatively young science, growing along with interest in other aspects of the earth sciences in the mid-19th century. This section provides

4536-500: The gravitational attraction of the nearby Andes Mountains . However, the deflection was less than expected, which was attributed to the mountains having low-density roots that compensated for the mass of the mountains. In other words, the low-density mountain roots provided the buoyancy to support the weight of the mountains above the surrounding terrain. Similar observations in the 19th century by British surveyors in India showed that this

4620-430: The group include: Geomorphologist Earth 's surface is modified by a combination of surface processes that shape landscapes, and geologic processes that cause tectonic uplift and subsidence , and shape the coastal geography . Surface processes comprise the action of water, wind, ice, wildfire , and life on the surface of the Earth, along with chemical reactions that form soils and alter material properties,

4704-677: The landscape, they generally increase in size, merging with other rivers. The network of rivers thus formed is a drainage system . These systems take on four general patterns: dendritic, radial, rectangular, and trellis. Dendritic happens to be the most common, occurring when the underlying stratum is stable (without faulting). Drainage systems have four primary components: drainage basin , alluvial valley, delta plain, and receiving basin. Some geomorphic examples of fluvial landforms are alluvial fans , oxbow lakes , and fluvial terraces . Glaciers , while geographically restricted, are effective agents of landscape change. The gradual movement of ice down

4788-474: The landscape. Fluvial geomorphologists focus on rivers , how they transport sediment , migrate across the landscape , cut into bedrock , respond to environmental and tectonic changes, and interact with humans. Soils geomorphologists investigate soil profiles and chemistry to learn about the history of a particular landscape and understand how climate, biota, and rock interact. Other geomorphologists study how hillslopes form and change. Still others investigate

4872-691: The local climate, for example through orographic precipitation , which in turn modifies the topography by changing the hydrologic regime in which it evolves. Many geomorphologists are particularly interested in the potential for feedbacks between climate and tectonics , mediated by geomorphic processes. In addition to these broad-scale questions, geomorphologists address issues that are more specific or more local. Glacial geomorphologists investigate glacial deposits such as moraines , eskers , and proglacial lakes , as well as glacial erosional features, to build chronologies of both small glaciers and large ice sheets and understand their motions and effects upon

4956-465: The lower lithosphere have also been hypothesised to play important roles in the long term (> million year), large scale (thousands of km) evolution of the Earth's topography (see dynamic topography ). Both can promote surface uplift through isostasy as hotter, less dense, mantle rocks displace cooler, denser, mantle rocks at depth in the Earth. Marine processes are those associated with the action of waves, marine currents and seepage of fluids through

5040-516: The mid-20th century considered both un-innovative and dubious. Early climatic geomorphology developed primarily in continental Europe while in the English-speaking world the tendency was not explicit until L.C. Peltier's 1950 publication on a periglacial cycle of erosion. Climatic geomorphology was criticized in a 1969 review article by process geomorphologist D.R. Stoddart . The criticism by Stoddart proved "devastating" sparking

5124-857: The physics of landscapes. Geomorphologists may rely on geochronology , using dating methods to measure the rate of changes to the surface. Terrain measurement techniques are vital to quantitatively describe the form of the Earth's surface, and include differential GPS , remotely sensed digital terrain models and laser scanning , to quantify, study, and to generate illustrations and maps. Practical applications of geomorphology include hazard assessment (such as landslide prediction and mitigation ), river control and stream restoration , and coastal protection. Planetary geomorphology studies landforms on other terrestrial planets such as Mars. Indications of effects of wind , fluvial , glacial , mass wasting , meteor impact , tectonics and volcanic processes are studied. This effort not only helps better understand

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5208-478: The plates to be underthrust beneath the other plate. The result is that the crust in the collision zone becomes as much as 80 kilometers (50 mi) thick, versus 40 kilometers (25 mi) for average continental crust. As noted above , the Airy hypothesis predicts that the resulting mountain roots will be about five times deeper than the height of the mountains, or 32 km versus 8 km. In other words, most of

5292-423: The relationships between ecology and geomorphology. Because geomorphology is defined to comprise everything related to the surface of the Earth and its modification, it is a broad field with many facets. Geomorphologists use a wide range of techniques in their work. These may include fieldwork and field data collection, the interpretation of remotely sensed data, geochemical analyses, and the numerical modelling of

5376-675: The revised impact factor for the journal rose to 3.722 (articles published in 2017). The BSG can trace its beginnings back to a meeting in Sheffield in 1958 where British geomorphologists gathered together to organise a Landform Survey of Britain. By 1959 this group appears to have been referring to itself as the British Universities Geomorphological Research Group. This short-lived group agreed, at its second annual meeting, to disband itself and voted unanimously (all 19 of them) to constitute

5460-487: The role of biology in mediating surface processes can be definitively excluded are extremely rare, but may hold important information for understanding the geomorphology of other planets, such as Mars . Rivers and streams are not only conduits of water, but also of sediment . The water, as it flows over the channel bed, is able to mobilize sediment and transport it downstream, either as bed load , suspended load or dissolved load . The rate of sediment transport depends on

5544-760: The science of historical geology . While acknowledging its shortcomings, modern geomorphologists Andrew Goudie and Karna Lidmar-Bergström have praised it for its elegance and pedagogical value respectively. Geomorphically relevant processes generally fall into (1) the production of regolith by weathering and erosion , (2) the transport of that material, and (3) its eventual deposition . Primary surface processes responsible for most topographic features include wind , waves , chemical dissolution , mass wasting , groundwater movement, surface water flow, glacial action , tectonism , and volcanism . Other more exotic geomorphic processes might include periglacial (freeze-thaw) processes, salt-mediated action, changes to

5628-409: The science of geomorphology. The model or theory has never been proved wrong, but neither has it been proven. The inherent difficulties of the model have instead made geomorphological research to advance along other lines. In contrast to its disputed status in geomorphology, the cycle of erosion model is a common approach used to establish denudation chronologies , and is thus an important concept in

5712-532: The sea, eventually those seas would fill while the land lowered. He claimed that this would mean that land and water would eventually swap places, whereupon the process would begin again in an endless cycle. The Encyclopedia of the Brethren of Purity published in Arabic at Basra during the 10th century also discussed the cyclical changing positions of land and sea with rocks breaking down and being washed into

5796-525: The sea, their sediment eventually rising to form new continents. The medieval Persian Muslim scholar Abū Rayhān al-Bīrūnī (973–1048), after observing rock formations at the mouths of rivers, hypothesized that the Indian Ocean once covered all of India . In his De Natura Fossilium of 1546, German metallurgist and mineralogist Georgius Agricola (1494–1555) wrote about erosion and natural weathering . Another early theory of geomorphology

5880-755: The seabed caused by marine currents, seepage of fluids through the seafloor or extraterrestrial impact. Aeolian processes pertain to the activity of the winds and more specifically, to the winds' ability to shape the surface of the Earth . Winds may erode, transport, and deposit materials, and are effective agents in regions with sparse vegetation and a large supply of fine, unconsolidated sediments . Although water and mass flow tend to mobilize more material than wind in most environments, aeolian processes are important in arid environments such as deserts . The interaction of living organisms with landforms, or biogeomorphologic processes , can be of many different forms, and

5964-459: The seafloor. Mass wasting and submarine landsliding are also important processes for some aspects of marine geomorphology. Because ocean basins are the ultimate sinks for a large fraction of terrestrial sediments, depositional processes and their related forms (e.g., sediment fans, deltas ) are particularly important as elements of marine geomorphology. There is a considerable overlap between geomorphology and other fields. Deposition of material

6048-407: The stability and rate of change of topography under the force of gravity , and other factors, such as (in the very recent past) human alteration of the landscape. Many of these factors are strongly mediated by climate . Geologic processes include the uplift of mountain ranges , the growth of volcanoes , isostatic changes in land surface elevation (sometimes in response to surface processes), and

6132-596: The surface, depending on whether the new material is denser or less dense than the rock it displaces. Tectonic effects on geomorphology can range from scales of millions of years to minutes or less. The effects of tectonics on landscape are heavily dependent on the nature of the underlying bedrock fabric that more or less controls what kind of local morphology tectonics can shape. Earthquakes can, in terms of minutes, submerge large areas of land forming new wetlands. Isostatic rebound can account for significant changes over hundreds to thousands of years, and allows erosion of

6216-434: The thickened crust moves downwards rather than up, just as most of an iceberg is below the surface of the water. However, convergent plate margins are tectonically highly active, and their surface features are partially supported by dynamic horizontal stresses, so that they are not in complete isostatic equilibrium. These regions show the highest isostatic anomalies on the Earth's surface. Mid-ocean ridges are explained by

6300-408: The thickness of the crust. This hypothesis was suggested to explain how large topographic loads such as seamounts (e.g. Hawaiian Islands ) could be compensated by regional rather than local displacement of the lithosphere. This is the more general solution for lithospheric flexure , as it approaches the locally compensated models above as the load becomes much larger than a flexural wavelength or

6384-560: The uplifted shorelines of Lake Bonneville . The concept was further developed in the 1950s by the Dutch geodesist Vening Meinesz . Three principal models of isostasy are used: Airy and Pratt isostasy are statements of buoyancy, but flexural isostasy is a statement of buoyancy when deflecting a sheet of finite elastic strength. In other words, the Airy and Pratt models are purely hydrostatic, taking no account of material strength, while flexural isostacy takes into account elastic forces from

6468-401: The water (ca. 1,000 kg m ). Thus, generally: For the simplified model shown the new density is given by: ρ 1 = ρ c c h 1 + c {\displaystyle \rho _{1}=\rho _{c}{\frac {c}{h_{1}+c}}} , where h 1 {\displaystyle h_{1}} is the height of the mountain and c

6552-531: The word 'isostasy' in 1889 to describe this general phenomenon. However, two hypotheses to explain the phenomenon had by then already been proposed, in 1855, one by George Airy and the other by John Henry Pratt . The Airy hypothesis was later refined by the Finnish geodesist Veikko Aleksanteri Heiskanen and the Pratt hypothesis by the American geodesist John Fillmore Hayford . Both the Airy-Heiskanen and Pratt-Hayford hypotheses assume that isostacy reflects

6636-434: Was German, and during his lifetime his ideas were at times rejected vigorously by the English-speaking geomorphology community. His early death, Davis' dislike for his work, and his at-times-confusing writing style likely all contributed to this rejection. Both Davis and Penck were trying to place the study of the evolution of the Earth's surface on a more generalized, globally relevant footing than it had been previously. In

6720-503: Was a widespread phenomenon in mountainous areas. It was later found that the difference between the measured local gravitational field and what was expected for the altitude and local terrain (the Bouguer anomaly ) is positive over ocean basins and negative over high continental areas. This shows that the low elevation of ocean basins and high elevation of continents is also compensated at depth. The American geologist Clarence Dutton use

6804-444: Was an elaboration of the uniformitarianism theory that had first been proposed by James Hutton (1726–1797). With regard to valley forms, for example, uniformitarianism posited a sequence in which a river runs through a flat terrain, gradually carving an increasingly deep valley, until the side valleys eventually erode, flattening the terrain again, though at a lower elevation. It was thought that tectonic uplift could then start

6888-416: Was better described as an alternation between ongoing processes of uplift and denudation, as opposed to Davis's model of a single uplift followed by decay. He also emphasised that in many landscapes slope evolution occurs by backwearing of rocks, not by Davisian-style surface lowering, and his science tended to emphasise surface process over understanding in detail the surface history of a given locality. Penck

6972-507: Was devised by Song dynasty Chinese scientist and statesman Shen Kuo (1031–1095). This was based on his observation of marine fossil shells in a geological stratum of a mountain hundreds of miles from the Pacific Ocean . Noticing bivalve shells running in a horizontal span along the cut section of a cliffside, he theorized that the cliff was once the pre-historic location of a seashore that had shifted hundreds of miles over

7056-402: Was foreshadowed by the work of Wladimir Köppen , Vasily Dokuchaev and Andreas Schimper . William Morris Davis , the leading geomorphologist of his time, recognized the role of climate by complementing his "normal" temperate climate cycle of erosion with arid and glacial ones. Nevertheless, interest in climatic geomorphology was also a reaction against Davisian geomorphology that was by

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