Geomorphology (from Greek: γη, "ge", "earth"; μορφή, "morfé", "form"; and λόγος, "
logos", "knowledge") is the study of landformsand the processes that shape them. Geomorphologists seek to understand why landscapes look the way they do: to understand landform history and dynamics, and predict future changes through a combination of field observation, physical experiment, and numerical modeling. Geomorphology is practiced within geology, geodesy, geography, archaeology, and civil and environmental engineering. Early studies in geomorphology are the foundation for pedology, one of two main branches of soil science.
Landforms evolve in response to a combination of natural and
anthropogenicprocesses. The landscape is built up through tectonic upliftand volcanism. Denudationoccurs by erosionand mass wasting, which produces sediment that is transported and deposited elsewhere within the landscape or off the coast. Landscapes are also lowered by subsidence, either due to tectonics or physical changes in underlying sedimentary deposits. These processes are each influenced differently by climate, ecology, and human activity.
Practical applications of geomorphology include measuring the effects of climate change, hazard assessments including
landslideprediction and mitigation, rivercontrol and restoration, coastal protection, and assessing the presence of water on Mars.
Perhaps the earliest one to devise a theory of geomorphology was the polymath Chinese scientist and statesman
Shen Kuo(1031-1095 AD). This was based on his observation of marine fossilshells in a geological stratumof 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 the centuries. He inferred that the land was reshaped and formed by soil erosionof the mountains and by deposition of silt, after observing strange natural erosions of the Taihang Mountainsand the Yandang Mountain near Wenzhou. Furthermore, he promoted the theory of gradual climate changeover centuries of time once ancient petrified bamboos were found to be preserved underground in the dry, northern climate zone of "Yanzhou", which is now modern day Yan'an, Shaanxiprovince.
The first geomorphic model was the "geographical cycle" or the "cycle of erosion", developed by
William Morris Davisbetween 1884 and 1899. The cycle was inspired by theories of uniformitarianism which were first formulated by James Hutton(1726-1797). Concerning valley forms, the cycle was depicted as a sequence by which a river would cut a valley more and more deeply, but then erosion of side valleys would eventually flatten out the terrain again, now at a lower elevation. The cycle could be started over by upliftof the terrain. The model is today considered too much of a simplification to be especially useful in practice.. Walther Penckdeveloped an alternative model in the 1920s, based on ratios of uplift and erosion, but it was also too weak to explain a variety of landforms. G. K. Gilbertwas an important early American geomorphologist.
Modern geomorphology focuses on the quantitative analysis of interconnected processes, such as the contribution of solar energy, the rates of steps of the
hydrologic cycle, plate movement rates from geophysicsto compute the age and expected fate of landforms and the weatheringand erosionof the land. The use of more precise measurement technique has also enabled processes like erosion to be observed directly, rather than merely surmised from other evidence. Computer simulationis also valuable for testing that a particular model yields results with properties similar to real terrain.
Primary surface processes responsible for most topographic features include
wind, waves, weathering, mass wasting, ground water, surface water, glaciers, tectonism, and volcanism.
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 bedload, suspended loador dissolved load. The rate of sediment transport depends on the availability of sediment itself and on the river's discharge.
As rivers flow across the landscape, they generally increase in size, merging with other rivers. The network of rivers thus formed is a
drainage systemand is often dendritic, but may adopt other patterns depending on the regional topography and underlying geology.
Soil, regolith, and rock move downslope under the force of gravityvia creep, slides, flows, topples, and falls. Such mass wastingoccurs on both terrestrial and submarine slopes, and has been observed on Earth, Mars, and Venus.
Glaciers, while geographically restricted, are effective agents of landscape change. The gradual movement of icedown 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.
This results from chemical dissolution of rock and from the mechanical wearing of rock by plant roots, ice expansion, and the abrasive action of sediment. Weathering provides the source of the sediment transported by fluvial, glacial, aeolian, or
Different geomorphological processes dominate at different spatial and temporal scales. To help categorize landscape scales some geomorphologists use the following
* 1st -
Continent, oceanbasin, climatic zone (~10,000,000 km2)
* 2nd - Shield, e.g.
Baltic shield, or mountain range(~1,000,000 km2)
* 3rd - Isolated
sea, Sahel(~100,000 km2)
* 4th - Massif, e.g.
Massif Centralor Group of related landforms, e.g., Weald(~10,000 km2)
* 5th - River valley,
* 6th - Individual
mountainor volcano, small valleys (~100 km2)
* 7th - Hillslopes, stream channels,
* 8th -
gully, barchannel(~1 km2)
* 9th - Meter-sized features
* Drainage system
Fluvial landforms of streams
* Hydrologic modeling,
behavioral modeling in hydrology
Soils retrogression and degradation
* Important publications in geomorphology
*cite book |last=Selby |first=Michael John |title=Earth's changing surface: an introduction to geomorphology |publisher=Clarendon Press |location=Oxford |year=1985 |isbn=0-19-823252-7
*cite book |last=Chorley |first=Richard J. |authorlink=Richard Chorley |coauthors=Stanley Alfred Schumm and David E. Sugden |title=Geomorphology |publisher=Methuen |location=London |year=1985 |isbn=0-416-32590-4
*cite book |first=Bernhard |last=Edmaier |authorlink=Bernhard Edmaier |title=Earthsong |publisher=
Phaidon Press|location=London |year=2004|isbn=0-7148-4451-9
*cite book |last=Scheidegger |first=Adrian E. |title=Morphotectonics |publisher=Springer |location=Berlin |year=2004 |isbn=3-540-20017-7
*cite book |last=Needham |first=Joseph |authorlink=Joseph Needham |title=Science and civilisation in China |publisher=Cambridge University Press |location=Cambridge, UK |year=1954 |isbn=0-521-05801-5
*cite book |last=Kondolf |first=G. Mathias |coauthors=Hervé Piégay |title=Tools in fluvial geomorphology |publisher=Wiley |location=New York |year=2003 |isbn=0-471-49142-X
* [http://sagehen.ucnrs.org/courses/geomorph.htm Geomorphic and Ecological Fundamentals for River and Stream Restoration] : includes a listing of instructors & additional short courses in Geomorphology topics taught by this group.
* [http://www.geomorph.org International Association of Geomorphologists]
* [http://aag-gsg.org Geomorphology in the Association of American Geographers]
* [http://www.geomorphology.org.uk British Society for Geomorphology]
* [http://www.sgp.org.pl Association of Polish Geomorphologists]
* [http://www.giub.uni-bonn.de/akgeomorphologie/englishindex.html German Geomorphologists Group (Deutscher Arbeitskreis fuer Geomorphologie]
* [http://www.sgp.org.pl/gw/wmd/wmd.html Model of landscape evolution by William Morris Davis (by GEOMORPHLIST)]
* [http://www.abdn.ac.uk/~geo337/gg4514/davis.htm The Geographical Cycle, or the Cycle of Erosion (1899)]
* [http://disc.gsfc.nasa.gov/geomorphology/index.shtml Geomorphology from Space] (by NASA)
* [http://websoilsurvey.nrcs.usda.gov/app/WebSoilSurvey.aspx USDA-NRCS Web Soil Survey] Survey of surficial geologic deposits and geomorphology across the U.S.
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