This articleneeds additional citations forverification.(May 2013) |
Avalleyis an elongated low area often running betweenhillsormountains,which typically contains ariverorstreamrunning from one end to the other. Most valleys are formed byerosionof the land surface by rivers or streams over a very long period. Some valleys are formed through erosion byglacial ice.These glaciers may remain present in valleys in high mountains or polar areas.
![](https://upload.wikimedia.org/wikipedia/commons/thumb/a/a3/Glacier_park1.jpg/220px-Glacier_park1.jpg)
![](https://upload.wikimedia.org/wikipedia/commons/thumb/1/1d/Romsdalen.jpg/220px-Romsdalen.jpg)
![](https://upload.wikimedia.org/wikipedia/commons/thumb/e/ee/Flj%C3%B3tsdalur.jpg/220px-Flj%C3%B3tsdalur.jpg)
![](https://upload.wikimedia.org/wikipedia/commons/thumb/3/3e/Vale_dos_Frades.jpg/220px-Vale_dos_Frades.jpg)
At lower latitudes and altitudes, theseglacially formedvalleys may have been created or enlarged duringice agesbut now are ice-free and occupied by streams or rivers. Indesertareas, valleys may be entirely dry or carry a watercourse only rarely. Inareas of limestone bedrock,dry valleysmay also result from drainage now taking placeundergroundrather than at the surface.Rift valleysarise principally fromearth movements,rather than erosion. Many different types of valleys are described by geographers, using terms that may be global in use or else applied only locally.
Formation of valleys
editValleys may arise through several different processes. Most commonly, they arise fromerosionover long periods bymoving waterand are known as river valleys. Typically small valleys containing streams feed into larger valleys which in turn feed into larger valleys again, eventually reaching the ocean or perhaps aninternal drainage basin.In polar areas and at high altitudes, valleys may be eroded byglaciers;these typically have a U-shaped profile in cross-section, in contrast to river valleys, which tend to have a V-shaped profile. Other valleys may arise principally through tectonic processes such asrifting.All three processes can contribute to the development of a valley over geological time. The flat (or relatively flat) portion of a valley between its sides is referred to as the valley floor. The valley floor is typically formed by river sediments and may havefluvial terraces.
River valleys
editThe development of a river valley is affected by the character of the bedrock over which the river or stream flows, the elevational difference between its top and bottom, and indeed the climate. Typically the flow will increase downstream and the gradient will decrease. In the upper valley, the stream will most effectively erode its bed throughcorrasionto produce a steep-sided V-shaped valley. The presence of more resistant rock bands, ofgeological faults,fractures,andfoldsmay determine the course of the stream and result in a twisting course withinterlocking spurs.
In the middle valley, as numerous streams have coalesced, the valley is typically wider, the flow slower and both erosion and deposition may take place. More lateral erosion takes place in the middle section of a river's course, as strong currents on the outside of its curve erode the bank. Conversely, deposition may take place on the inside of curves where the current is much slacker, the process leading to the river assuming ameanderingcharacter. In the lower valley, gradients are lowest, meanders may be much broader and a broaderfloodplainmay result. Deposition dominates over erosion.[1][2]A typical river basin ordrainage basinwill incorporate each of these different types of valleys.
Some sections of a stream or river valleys may have vertically incised their course to such an extent that the valley they occupy is best described as agorge,ravine,orcanyon.Rapid down-cutting may result from localized uplift of the land surface or rejuvenation of the watercourse as a result for example of a reduction in the base level to which the river is eroded, e.g. lowered global sea level during anice age.Suchrejuvenationmay also result in the production ofriver terraces.[3]
Glacial valleys
editThere are various forms of valleys associated with glaciation. True glacial valleys are those that have been cut by a glacier which may or may not still occupy the valley at the present day. Such valleys may also be known as glacial troughs. They typically have aU-shaped cross-sectionand are characteristic landforms of mountain areas where glaciation has occurred or continues to take place.[4]
The uppermost part of a glacial valley frequently consists of one or more 'armchair-shaped' hollows, or 'cirques', excavated by the rotational movement downslope of a cirque glacier. During glacial periods, for example, thePleistoceneice ages, it is in these locations that glaciers initially form and then, as theice ageproceeds, extend downhill through valleys that have previously been shaped by water rather than ice.Abrasionby rock material embedded within the moving glacial ice causes the widening and deepening of the valley to produce the characteristic U or trough shape with relatively steep, even vertical sides and a relatively flat bottom.
Interlocking spursassociated with the development of river valleys are preferentially eroded to producetruncated spurs,typical of glaciated mountain landscapes. The upper end of the trough below the ice-contributing cirques may be atrough-end.Valley steps(or 'rock steps') can result from differing erosion rates due to both the nature of the bedrock (hardness and jointing for example) and the power of the moving ice. In places, a rock basin may be excavated which may later be filled with water to form aribbon lakeor else by sediments. Such features are found in coastal areas asfjords.The shape of the valley which results from all of these influences may only become visible upon the recession of the glacier that forms it.[5]A river or stream may remain in the valley; if it is smaller than one would expect given the size of its valley, it can be considered an example of amisfit stream.
Other interesting glacially carved valleys include:
- Yosemite Valley(United States)
- Side valleysof the Austrian riverSalzachfor their parallel directions and hanging mouths.
- That of theSt. Mary RiverinGlacier National ParkinMontana,United States.
Tunnel
editA tunnel valley is a large, long, U-shaped valley originally cut under the glacial ice near the margin of continental ice sheets such as that now covering Antarctica and formerly covering portions of all continents during past glacial ages.[6]Such valleys can be up to 100 km (62 mi) long, 4 km (2.5 mi) wide, and 400 m (1,300 ft) deep (its depth may vary along its length). Tunnel valleys were formed by subglacialwater erosion.They once served as subglacial drainage pathways carrying large volumes of meltwater. Their cross-sections exhibit steep-sided flanks similar to fjord walls, and their flat bottoms are typical of subglacial glacial erosion.
Meltwater
editIn northern Central Europe, the Scandinavian ice sheet during the various ice ages advanced slightly uphill against the lie of the land. As a result, its meltwaters flowed parallel to the ice margin to reach the North Sea basin, forming huge, flat valleys known asUrstromtäler.Unlike the other forms of glacial valleys, these were formed by glacial meltwaters.
Transition forms and shoulders
editDepending on thetopography,therock types,and theclimate,a variety of transitional forms between V-, U- and plain[clarification needed]valleys can form. The floor or bottom of these valleys can be broad or narrow, but all valleys have a shoulder. The broader a mountain valley, the lower its shoulders are located in most cases. An important exception is canyons where the shoulder almost is near the top of the valley's slope. In the Alps – e.g. theTyroleanInnvalley – the shoulders are quite low (100–200 meters above the bottom). Many villages are located here (esp. on the sunny side) because the climate is very mild: even in winter when the valley's floor is filled with fog, these villages are insunshine.
In some stress-tectonic regions of theRocky Mountainsor the Alps (e.g.Salzburg), theside valleysare parallel to each other, and arehanging.Smaller streams flow into rivers as deep canyons orwaterfalls.
Hanging tributary
editA hanging valley is atributaryvalley that is higher than the main valley. They are most commonly associated with U-shaped valleys, where a tributary glacier flows into a glacier of larger volume. The main glacier erodes a deep U-shaped valley with nearly vertical sides, while the tributary glacier, with a smaller volume of ice, makes a shallower U-shaped valley. Since the surfaces of the glaciers were originally at the sameelevation,the shallower valley appears to be 'hanging' above the main valley. Often, waterfalls form at or near the outlet of the upper valley.[7]
Hanging valleys also occur infjordsystems underwater. The branches ofSognefjordare much shallower than the main fjord. The mouth ofFjærlandsfjordis about 400 meters (1,300 ft) deep while the main fjord nearby is 1,200 meters (3,900 ft) deep. The mouth ofIkjefjordis only 50 meters (160 ft) deep while the main fjord is around 1,300 meters (4,300 ft) at the same point.[8]
Glaciated terrain is not the only site of hanging streams and valleys. Hanging valleys are also simply the product of varying rates of erosion of the main valley and the tributary valleys. The varying rates of erosion are associated with the composition of the adjacent rocks in the different valley locations. The tributary valleys are eroded and deepened by glaciers or erosion at a slower rate than that of the main valley floor; thus the difference in the two valleys' depth increases over time. The tributary valley, composed of more resistant rock, then hangs over the main valley.[9]
Trough-shaped
editTrough-shaped valleys also form in regions of heavy topographicdenudation.By contrast with glacial U-shaped valleys, there is less downward and sideways erosion. The severe downslope denudation results in gently sloping valley sides; their transition to the actual valley bottom is unclear. Trough-shaped valleys occur mainly inperiglacialregions and intropicalregions of variable wetness. Both climates are dominated by heavy denudation.[10]
Box
editBox valleys have wide, relatively level floors and steep sides. They are common in periglacial areas and occur in mid-latitudes, but also occur in tropical and arid regions.[11]
Rift
editRift valleys, such as theAlbertine RiftandGregory Riftare formed by the expansion of theEarth's crust due totectonicactivity beneath the Earth's surface.
Terms for valleys
editThere are many terms used for different sorts of valleys. They include:
- Cove:A small valley, closed at one or both ends, in the central or southernAppalachian Mountainswhich sometimes results from the erosion of ageologic window.
- Dell:A small, secluded, and often wooded valley.
- Dry valley:A valley not created by sustained surface water flow.
- Erosional valley: A valley formed byerosion.
- Hollow: A term used regionally for a small valley surrounded by mountains orridges.InIreland,New England,Appalachia,and theOzarksofArkansasandMissouri,a hollow is a small valley or drystream bed.
- Longitudinal valley:An elongated valley found between two nearly-parallel mountain chains.
- Steephead valley:A deep, narrow, flat-bottomed valley with an abrupt ending.
- Strike valley:A valley typically developed parallel to acuestafrom more readily eroded strata.
- Structural valley:A valley formed by geologic events such as drop faults or the rise of highlands.[12]
Similar geographical features such asgullies,chines,andkloofs,are not usually referred to as valleys.
British regional terms for valleys
editThe termscorrie,glen,andstrathare allAnglicisationsofGaelicterms and are commonly encountered in place-names inScotlandand other areas where Gaelic was once widespread. Strath signifies a wide valley between hills, the floor of which is either level or slopes gently.[13]A glen is a river valley which is steeper and narrower than a strath.[14]A corrie is a basin-shaped hollow in a mountain.[15]Each of these terms also occurs in parts of the world formerlycolonized by Britain.Corrieis used more widely by geographers as a synonym for (glacial)cirque,as is the wordcwmborrowed fromWelsh.[16]
The worddaleoccurs widely in place names in the north of England and, to a lesser extent, in southern Scotland. As a generic name for a type of valley,the termtypically refers to a wide valley, though there are many much smaller stream valleys within theYorkshire Daleswhich are named "(specific name) Dale".[17]Cloughis a word in common use in northern England for a narrow valley with steep sides.[18]Gillis used to describe a ravine containing a mountain stream inCumbriaand thePennines.[19]The termcombe(also encountered ascoombe) is widespread in southern England and describes a short valley set into a hillside.[20]Other terms for small valleys such as hope, dean, slade, slack and bottom are commonly encountered in place-names in various parts of England but are no longer in general use as synonyms forvalley.
The term valeis used in England and Wales to describe a wide river valley, usually with a particularly wideflood plainor flat valley bottom. In Southern England, vales commonly occur between the outcrops of different relatively erosion-resistant rock formations, where lessresistantrock, oftenclaystonehas been eroded. An example is theVale of White Horsein Oxfordshire.
Human settlement
editSome of the first humancomplex societiesoriginated in river valleys, such as that of theNile,Tigris-Euphrates,Indus,Ganges,Yangtze,Yellow River,Mississippi,and arguably theAmazon.Inprehistory,the rivers were used as a source offresh waterand food (fish and game), as well as a place to wash and a sewer. The proximity of water moderatedtemperatureextremes and provided a source forirrigation,stimulating the development ofagriculture.Most of thefirst civilizationsdeveloped from these river valley communities. Siting of settlements within valleys is influenced by many factors, including the need to avoid flooding and the location of river crossing points.
Notable examples
editAfrica
edit- Albertine Rift
- East African Rift
- Ethiopian Rift Valley
- Great Rift Valley
- Nile Valley(Egypt/Sudan/Ethiopia/Uganda)
- Nugaal Valley(Somalia)
- Umba Valley(Tanzania)
- Valley of the Kings(Egypt)
Asia
edit- List of valleys in India
- List of valleys in Pakistan
- Beqaa Valley(Lebanon)
- Dang Valley(Western Nepal)
- Emin Valley(Kazakhstan)
- Ihlara,Turkey
- Jordan Rift Valley(Jordan - Israel)
- Jordan Valley
- Kathmandu(Nepal)
- Klang Valley(Malaysia)
- Mahaweli(Sri Lanka)
- Panjshir Valley(Afghanistan)
- Valleys of China
Oceania
edit- Barossa Valley(Australia)
- Bulolo Valley(Papua New Guinea)
- Cagayan Valley(Philippines)
- Capertee Valley(Australia)
- Hunter Valley(Australia)
- Hutt Valley(New Zealand)
- Kangaroo Valley(Australia)
- Markham Valley(Papua New Guinea)
- Strath Taieri(New Zealand)
- Swan Valley(Australia)
Europe
edit- Bergensdalen(Vestland, Norway)
- Dalen, Telemark(Telemark, Norway)
- Danube Valley(Eastern Europe)
- Evrotas Valley,Sparta(Greece)
- Glen Coe(Scotland, United Kingdom)
- Great Glen(Scotland, United Kingdom)
- Gudbrandsdalen(Oppland, Norway)
- Hallingdalen(Buskerud, Norway)
- Heddal(Telemark, Norway)
- Iron Gate(Romania/Serbia)
- Lauterbrunnen Valley(Bern, Switzerland)
- Loire Valleywith its famous castles (France)
- Midt-Telemark(Telemark, Norway)
- Nant Ffrancon(Wales, United Kingdom)
- Numedalen(Buskerud, Norway)
- Østerdalen(Hedmark, Norway)
- Po Valley,(Italy)
- Rhone Valleyfrom theMatterhornto Grenoble andLyon(France)
- Romsdalen(Møre Og Romsdal, Norway)
- Setesdal(Agder, Norway)
- South Wales Valleys(Wales, United Kingdom)
- Upper RhineValley orUpper Rhine Plain,an oldgrabensystem. (France and Germany)
- Vestfjorddalen(Norway)
North America
edit- Central Valley(California)
- Coachella Valley(California)
- Cumberland Valley(Maryland/Pennsylvania)
- Cuyahoga Valley(Ohio)
- Death Valley(California)
- Fraser Canyon(British Columbia)
- Fraser Valley(British Columbia)
- Grand Canyon(Arizona, United States)
- Hell's Gate(British Columbia)
- Hudson Valley(New York)
- Imperial Valley(California)
- Las Vegas Valley(Nevada)
- Missouri River Valley(Missouri)
- Monument Valley(Arizona, Utah)
- Napa Valley(California)
- Okanagan Valley(British Columbia)
- Ottawa Valley(Ontario/Quebec)
- Palo Duro Canyon(Texas)
- Valley of the Sun(Arizona)
- Rio Grande Valley(Texas)
- Saint Lawrence Valley(Ontario/Quebec/New York)
- Salt Lake Valley(Utah)
- San Fernando Valley(California)
- Shenandoah Valley(Virginia/West Virginia)
- Sonoma Valley(California)
- Toluca Valley(Mexico)
- Valley of the Gods(Utah)
- Valley of Mexico(Mexico)
- Willamette Valley(Oregon)
- Yosemite Valley(California)
South America
edit- Aburra Valley(Colombia)
- Calchaquí Valleys(Argentina)
- Cauca Valley(Colombia)
- IschigualastoValley of the Moon(Argentina)
- Paraíba Valley(Brazil)
Antarctica
editExtraterrestrial valleys
editNumerous elongate depressions have been identified on the surface ofMars,Venus,theMoon,and otherplanets and their satellitesand are known asvalles(singular: 'vallis'). Deeper valleys with steeper sides (akin to canyons) on certain of these bodies are known aschasmata(singular: 'chasma'). Long narrow depressions are referred to asfossae(singular: 'fossa').[21]These are theLatinterms for 'valley, 'gorge' and 'ditch' respectively. The German term 'rille' or Latin term 'rima' (signifying 'cleft') is used for certain other elongate depressions on the Moon.[22]
See also:
See also
edit- Canyon– Deep chasm between cliffs
- Grass valley– Meadow within a forested and relatively small drainage basin
- Gully– Landform created by running water and/or mass movement eroding sharply into soil
- Stream channel– Narrow body of water
References
edit- ^Monkhouse, F.J. (1971).Principles of Physical Geography(Seventh ed.). London: University of London Press Ltd. pp. 152–157.ISBN0340090227.
- ^Morisawa, Marie(1968). Rhodes W. Fairbridge (ed.).Classification of Rivers.New York: Reinhold Book Corporation. pp. 956–957.OCLC2968.
- ^Monkhouse, F.J. (1971).Principles of Physical Geography(Seventh ed.). London: University of London Press Ltd. pp. 161–164.ISBN0340090227.
- ^"Vale of Eden".Britannica.Retrieved20 December2020.
- ^Monkhouse, F.J. (1971).Principles of Physical Geography(Seventh ed.). London: University of London Press Ltd. pp. 230–234.ISBN0340090227.
- ^Jørgensen, Flemming; Peter B.E. Sandersen (June 2006). "Buried and open tunnel valleys in Denmark—erosion beneath multiple ice sheets".Quaternary Science Reviews.25(11–12): 1339–1363.Bibcode:2006QSRv...25.1339J.doi:10.1016/j.quascirev.2005.11.006.
- ^"Glossary of Glacier Terminology".U.S. Geological Survey. May 28, 2004.Retrieved2007-05-24.
- ^Nesje, A., & Whillans, I. M. (1994). Erosion of Sognefjord, Norway.Geomorphology,9(1), 33-45.
- ^"Illustrated Glossary of Alpine Glacial Landforms - Hanging Valley"..uwsp.edu.Retrieved2011-10-03.
- ^Rowley, Taylor; Giardino, John R.; Granados-Aguilar, Raquel; Vitek, John D. (2015-01-01), Giardino, John R.; Houser, Chris (eds.),Chapter 13 - Periglacial Processes and Landforms in the Critical Zone,Developments in Earth Surface Processes, vol. 19, Elsevier, pp. 397–447,doi:10.1016/B978-0-444-63369-9.00013-6,ISBN978-0-444-63369-9,retrieved2023-10-19
- ^Goudie, Andrew, ed. (2004).Encyclopedia of Geomorphology.Psychology Press. p. 98.ISBN9780415327381.
- ^"Early History, Santa Clara County".National Park Service.RetrievedJanuary 16,2015.
Santa Clara Valley is a structural valley, created by mountain building, as opposed to an erosional valley, or one which has undergone the wearing away of the earth's surface by natural agents.
- ^Ross, David (2001).Scottish Place-names(First ed.). Edinburgh: Birlinn. p. 203.ISBN1841581739.
- ^Ross, David (2001).Scottish Place-names(First ed.). Edinburgh: Birlinn. p. 99.ISBN1841581739.
- ^Ross, David (2001).Scottish Place-names(First ed.). Edinburgh: Birlinn. p. 53.ISBN1841581739.
- ^Whitten, D.G.A.; Brooks, J.R.V. (1972).Dictionary of Geology(First ed.). London: Penguin. p. 83.ISBN0140510494.
- ^"Bing maps".Microsoft Bing.Retrieved20 December2020.
- ^Gelling, Margaret (1984).Place-names in the Landscape: the Geographical roots of Britain's place-names(First ed.). London: J M Dent. p. 88.ISBN0460860860.
- ^Gelling, Margaret (1984).Place-names in the Landscape: the Geographical roots of Britain's place-names(First ed.). London: J M Dent. p. 99.ISBN0460860860.
- ^"Combe".Merriam–Webster's Dictionary.Merriam–Webster. 2011.
- ^"Gazetteer of Planetary Nomenclature, feature types".International Astronomical Union.Retrieved20 December2020.
- ^"Gazetteer of Planetary Nomenclature, Welcome".International Astronomical Union.Retrieved20 December2020.
External links
edit- NPS.gov,University of Wisconsin
- UWSP.edu,Glossary of Alpine Glacial Landforms
- "BGU.ac.il"(PDF).,SAR interferometry (analysis of valley forms in Fig.2 and 6)
- Valleys.com,Valleys of the World
- Valley definitions,YourDictionary
Extraterrestrial valleys
edit- ESA image:Vallis Alpes,bisecting the Lunar Alps
- Valles Marineris and Ophir Chasma,bilingualwebsite (EnglishandGerman)