Landform

A landform is a natural feature of the solid surface of the Earth or other planetary body. Landforms together make up a given terrain, and their arrangement in the landscape is known as topography. Typical landforms include hills, mountains, plateaus, canyons, and valleys, as well as shoreline features such as bays, peninsulas, and seas, including submerged features such as mid-ocean ridges, volcanoes, and the great ocean basins.

Cono de Arita, Salta. (Argentina)
This conical hill in Salar de Arizaro, Salta, Argentina called Cono de Arita constitutes a landform.

Physical characteristics

Landforms are categorized by characteristic physical attributes such as elevation, slope, orientation, stratification, rock exposure, and soil type. Gross physical features or landforms include intuitive elements such as berms, mounds, hills, ridges, cliffs, valleys, rivers, peninsulas, volcanoes, and numerous other structural and size-scaled (i.e. ponds vs. lakes, hills vs. mountains) elements including various kinds of inland and oceanic waterbodies and sub-surface features.

This panorama in Great Smoky Mountains National Park has the readily identifiable physical features of a rolling plain, actually part of a broad valley, distant foothills, and a backdrop of the old, much weathered Appalachian mountain range
This panorama in Great Smoky Mountains National Park has the readily identifiable physical features of a rolling plain, actually part of a broad valley, distant foothills, and a backdrop of the old, much weathered Appalachian mountain range

Hierarchy of classes

Oceans and continents exemplify the highest-order landforms. Landform elements are parts of a high-order landforms that can be further identified and systematically given a cohesive definition such as hill-tops, shoulders, saddles, foreslopes and backslopes.

Some generic landform elements including: pits, peaks, channels, ridges, passes, pools and plains.

Terrain (or relief) is the third or vertical dimension of land surface. Topography is the study of terrain, although the word is often used as a synonym for relief itself. When relief is described underwater, the term bathymetry is used. In cartography, many different techniques are used to describe relief, including contour lines and TIN (Triangulated irregular network).

Elementary landforms (segments, facets, relief units) are the smallest homogeneous divisions of the land surface, at the given scale/resolution. These are areas with relatively homogeneous morphometric properties, bounded by lines of discontinuity. A plateau or a hill can be observed at various scales ranging from few hundred meters to hundreds of kilometers. Hence, the spatial distribution of landforms is often scale-dependent as is the case for soils and geological strata.

A number of factors, ranging from plate tectonics to erosion and deposition, can generate and affect landforms. Biological factors can also influence landforms— for example, note the role of vegetation in the development of dune systems and salt marshes, and the work of corals and algae in the formation of coral reefs.

Landforms do not include man-made features, such as canals, ports and many harbors; and geographic features, such as deserts, forests, and grasslands. Many of the terms are not restricted to refer to features of the planet Earth, and can be used to describe surface features of other planets and similar objects in the Universe. Examples are mountains, hills, polar caps, and valleys, which are found on all of the terrestrial planets.

The scientific study of landforms is known as geomorphology.

Recent developments

Landforms may be extracted from a digital elevation model using some automated techniques where the data has been gathered by modern satellites and stereoscopic aerial surveillance cameras.[1] Until recently, compiling the data found in such data sets required time consuming and expensive techniques involving many man-hours. The most detailed DEMs available are measured directly using LIDAR techniques.

See also

References

  1. ^ Robert A. MacMillan; David H. McNabb; R. Keith Jones (September 2000). "Conference paper: "Automated landform classification using DEMs"". Retrieved 2008-06-26.

External links

Arête

An arête is a narrow ridge of rock which separates two valleys. It is typically formed when two glaciers erode parallel U-shaped valleys. Arêtes can also form when two glacial cirques erode headwards towards one another, although frequently this results in a saddle-shaped pass, called a col. The edge is then sharpened by freeze-thaw weathering, and the slope on either side of the arete steepened through mass wasting events and the erosion of exposed, unstable rock. The word ‘arête’ is actually French for edge or ridge; similar features in the Alps are described with the German equivalent term Grat.

Where three or more cirques meet, a pyramidal peak is created.

Cape (geography)

In geography, a cape is a headland or a promontory of large size extending into a body of water, usually the sea.

A cape usually represents a marked change in trend of the coastline which makes them prone to natural forms of erosion, mainly tidal actions. This results in capes having a relatively short geological lifespan. Capes can be formed by glaciers, volcanoes, and changes in sea level. Erosion plays a large role in each of these methods of formation.

Carr (landform)

A carr is a type of waterlogged wooded terrain that, typically, represents a succession stage between the original reedy swamp and the likely eventual formation of forest in a sub-maritime climate. The name derives from the Old Norse kjarr, meaning a swamp. The carr is one stage in a hydrosere: the progression of vegetation beginning from a terrain submerged by fresh water along a river or lake margin. In sub-maritime regions, it begins with reed-swamp. As the reeds decay, the soil surface eventually rises above the water, creating fens that allow vegetation such as sedge to grow. As this progression continues, riparian trees and bushes appear and a carr landscape is created – in effect a wooded fen in a waterlogged terrain. At this stage, overall, unlike the overwhelming acidity of decaying reeds, the pH is not too acidic and the soil is not too deficient in minerals, making a habitat for endemic and other wildlife. Characteristic trees include alder, willow and sallow.

Cirque

A cirque (French, from the Latin word circus) is an amphitheatre-like valley formed by glacial erosion. Alternative names for this landform are corrie (from Scottish Gaelic coire, meaning a pot or cauldron) and cwm (Welsh for "valley", pronounced [kʊm]). A cirque may also be a similarly shaped landform arising from fluvial erosion.

The concave shape of a glacial cirque is open on the downhill side, while the cupped section is generally steep. Cliff-like slopes, down which ice and glaciated debris combine and converge, form the three or more higher sides. The floor of the cirque ends up bowl-shaped as it is the complex convergence zone of combining ice flows from multiple directions and their accompanying rock burdens: hence it experiences somewhat greater erosion forces, and is most often overdeepened below the level of the cirque's low-side outlet (stage) and its down slope (backstage) valley. If the cirque is subject to seasonal melting, the floor of the cirque most often forms a tarn (small lake) behind a dam which marks the downstream limit of the glacial overdeepening: the dam itself can be composed of moraine, glacial till, or a lip of the underlying bedrock.The fluvial cirque or makhtesh, found in karst landscapes, is formed by intermittent river flow cutting through layers of limestone and chalk leaving sheer cliffs. A common feature for all fluvial-erosion cirques is a terrain which includes erosion resistant upper structures overlying materials which are more easily eroded.

Col

In geomorphology, a col is the lowest point on a mountain ridge between two peaks. It may also be called a gap. Particularly rugged and forbidding cols in the terrain are usually referred to as notches. They are generally unsuitable as mountain passes, but are occasionally crossed by mule tracks or climbers' routes. The term col tends to be associated more with mountain rather than hill ranges.The height of a summit above its highest col (called the key col) is effectively a measure of a mountain's topographic prominence. Cols lie on the line of the watershed between two mountains, often on a prominent ridge or arête. For example, the highest col in Austria, the Obere Glocknerscharte ("Upper Glockner Col", 3,766 m (AA)), lies between the Kleinglockner (3,783 m above sea level (AA)) and Großglockner (3,798 m above sea level (AA)) mountains, giving the Kleinglockner a minimum prominence of 17 metres.The majority of cols are unnamed and are either never transited or only crossed in the course of negotiating a ridge line. Many double summits are separated by prominent cols. The distinction with other names for breaks in mountain ridges such as saddle, wind gap or notch is not sharply defined and may vary from place to place.

Continent

A continent is one of several very large landmasses of the world. Generally identified by convention rather than any strict criteria, up to seven regions are commonly regarded as continents. Ordered from largest in area to smallest, they are: Asia, Africa, North America, South America, Antarctica, Europe, and Australia.Geologically, the continents largely correspond to areas of continental crust that are found on the continental plates. However, some areas of continental crust are regions covered with water not usually included in the list of continents. Zealandia is one such area (see submerged continents below).

Islands are frequently grouped with a neighbouring continent to divide all the world's land into geopolitical regions. Under this scheme, most of the island countries and territories in the Pacific Ocean are grouped together with the continent of Australia to form a geopolitical region called Oceania.

Crag and tail

A crag (sometimes spelled cragg, or in Scotland craig) is a rocky hill or mountain, generally isolated from other high ground. Crags are formed when a glacier or ice sheet passes over an area that contains a particularly resistant rock formation (often granite, a volcanic plug or some other volcanic structure). The force of the glacier erodes the surrounding softer material, leaving the rocky block protruding from the surrounding terrain. Frequently the crag serves as a partial shelter to softer material in the wake of the glacier, which remains as a gradual fan or ridge forming a tapered ramp (called the tail) up the leeward side of the crag.

In older examples, or those latterly surrounded by the sea, the tail is often missing, having been removed by post-glacial erosion.

Examples of such crag and tail formations include:

The Castle Rock in Edinburgh, Scotland, the rock on which Edinburgh Castle stands

Salisbury Crags and Arthur's Seat

North Berwick Law

Three in or near Stirling, including the rock on which Stirling Castle stands

"Scrabo Hill" in Newtownards, Northern Ireland ( Scrabo Tower stands on the erosion-resistant Crag)

Fluvial processes

In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluvioglacial is used.

Geography of Australia

The geography of Australia encompasses a wide variety of biogeographic regions being the world's smallest continent but the sixth-largest country in the world. The population of Australia is concentrated along the eastern and southeastern coasts. The geography of the country is extremely diverse, ranging from the snow-capped mountains of the Australian Alps and Tasmania to large deserts, tropical and temperate forests.

Neighbouring countries include Indonesia, East Timor and Papua New Guinea to the north, the Solomon Islands, Vanuatu and the French dependency of New Caledonia to the east, and New Zealand to the southeast.

Glacial landform

Glacial landforms are landforms created by the action of glaciers. Most of today's glacial landforms were created by the movement of large ice sheets during the Quaternary glaciations. Some areas, like Fennoscandia and the southern Andes, have extensive occurrences of glacial landforms; other areas, such as the Sahara, display rare and very old fossil glacial landforms.

Highland

Highlands or uplands are any mountainous region or elevated mountainous plateau. Generally speaking, upland (or uplands) refers to ranges of hills, typically up to 500–600 m. Highland (or highlands) is usually reserved for ranges of low mountains.

Kettle (landform)

A kettle (kettle hole, pothole) is a depression/hole in an outwash plain formed by retreating glaciers or draining floodwaters. The kettles are formed as a result of blocks of dead ice left behind by retreating glaciers, which become surrounded by sediment deposited by meltwater streams as there is increased friction. The ice becomes buried in the sediment and when the ice melts, a depression is left called a kettle hole, creating a dimpled appearance on the outwash plain. Lakes often fill these kettles, these are called kettle hole lakes. Another source is the sudden drainage of an ice-dammed lake. When the block melts, the hole it leaves behind is a kettle. As the ice melts, ramparts can form around the edge of the kettle hole. The lakes that fill these holes are seldom more than 10 m (33 ft) deep and eventually become filled with sediment. In acid conditions, a kettle bog may form but in alkaline conditions, it will be kettle peatland.

Peninsula

A peninsula (Latin: paeninsula from paene "almost” and insula "island") is a landform surrounded by water on the majority of its border while being connected to a mainland from which it extends. The surrounding water is usually understood to be continuous, though not necessarily named as a single body of water. Peninsulas are not always named as such; one can also be a headland, cape, island promontory, bill, point, or spit. A point is generally considered a tapering piece of land projecting into a body of water that is less prominent than a cape. A river which courses through a very tight meander is also sometimes said to form a "peninsula" within the (almost closed) loop of water. In English, the plural versions of peninsula are peninsulas and, less commonly, peninsulae.

Plain

In geography, a plain is a flat, sweeping landmass that generally does not change much in elevation. Plains occur as lowlands along the bottoms of valleys or on the doorsteps of mountains, as coastal plains, and as plateaus or uplands.In a valley, a plain is enclosed on two sides, but in other cases a plain may be delineated by a complete or partial ring of hills, by mountains, or by cliffs. Where a geological region contains more than one plain, they may be connected by a pass (sometimes termed a gap). Coastal plains would mostly rise from sea level until they run into elevated features such as mountains or plateaus.Plains are one of the major landforms on earth, where they are present on all continents, and would cover more than one-third of the world’s land area. Plains may have been formed from flowing lava, deposited by water, ice, wind, or formed by erosion by these agents from hills and mountains. Plains would generally be under the grassland (temperate or subtropical), steppe (semi-arid), savannah (tropical) or tundra (polar) biomes. In a few instances, deserts and rainforests can also be plains.Plains in many areas are important for agriculture because where the soils were deposited as sediments they may be deep and fertile, and the flatness facilitates mechanization of crop production; or because they support grasslands which provide good grazing for livestock.

Relict

A relict is a surviving remnant of a natural phenomenon.

In biology a relict (or relic) is an organism that at an earlier time was abundant in a large area but now occurs at only one or a few small areas.

In ecology, an ecosystem which originally ranged over a large expanse, but is now narrowly confined, may be termed a relict.

In geology, a relict is a structure or mineral from a parent rock that did not undergo metamorphosis when the surrounding rock did, or a rock that survived a destructive geologic process.

In geomorphology, a relict landform is a landform formed by either erosive or constructive surficial processes that are no longer active as they were in the past.

In agronomy, a relict crop is a crop which was previously grown extensively, but is now only used in one limited region, or a small number of isolated regions.

In history (as revealed in DNA testing), a relict population is an ancient people in an area who have been largely supplanted by a later group of migrants and their descendants.

In real estate law, reliction is the gradual recession of water from its usual high-water mark so that the newly uncovered land becomes the property of the adjoining riparian property owner.Other uses:

In addition, relict was an ancient term still used in colonial (British) America, and in England of that era, but now archaic, for a widow; it has come to be a generic or collective term for widows and widowers.

In historical linguistics, a relict is a word that is a survivor of a form or forms that are otherwise archaic.

Ria

A ria ( or ) is a coastal inlet formed by the partial submergence of an unglaciated river valley. It is a drowned river valley that remains open to the sea. Typically, rias have a dendritic, treelike outline although they can be straight and without significant branches. This pattern is inherited from the dendritic drainage pattern of the flooded river valley. The drowning of river valleys along a stretch of coast and formation of rias results in an extremely irregular and indented coastline. Often, there are naturally-occurring islands, which are summits of partly submerged, preexisting hill peaks. (Islands may also be artificial, such as those constructed for the Chesapeake Bay Bridge-Tunnel.)

A ria coast is a coastline having several parallel rias separated by prominent ridges, extending a distance inland. The sea level change that caused the submergence of a river valley may be either eustatic (where global sea levels rise), or isostatic (where the local land sinks). The result is often a very large estuary at the mouth of a relatively insignificant river (or else sediments would quickly fill the ria). The Kingsbridge Estuary in Devon, England, is an extreme example of a ria forming an estuary disproportionate to the size of its river; no significant river flows into it at all, only a number of small streams.

Shoal

In oceanography, geomorphology, and earth sciences, a shoal is a natural submerged ridge, bank, or bar that consists of, or is covered by, sand or other unconsolidated material, and rises from the bed of a body of water to near the surface. Often it refers to those submerged ridges, banks, or bars that rise near enough to the surface of a body of water as to constitute a danger to navigation. Shoals are also known as sandbanks, sandbars, or gravelbars. Two or more shoals that are either separated by shared troughs or interconnected by past or present sedimentary and hydrographic processes are referred to as a shoal complex.The term shoal is also used in a number of ways that can be either similar or quite different from how it is used in the geologic, geomorphic, and oceanographic literature. Sometimes, this terms refers to either any relatively shallow place in a stream, lake, sea, or other body of water; a rocky area on the sea floor within an area mapped for navigation purposes; a growth of vegetation on the bottom of a deep lake that occurs at any depth; and as a verb for the process of proceeding from a greater to a lesser depth of water.

Spit (landform)

A spit or sandspit is a deposition bar or beach landform off coasts or lake shores. It develops in places where re-entrance occurs, such as at a cove's headlands, by the process of longshore drift by longshore currents. The drift occurs due to waves meeting the beach at an oblique angle, moving sediment down the beach in a zigzag pattern. This is complemented by longshore currents, which further transport sediment through the water alongside the beach. These currents are caused by the same waves that cause the drift.

Table (landform)

A table or tableland is a butte, flank of a mountain, or mountain, that has a flat top.

This kind of landform has numerous names, including:

Tuya

Tepui

Mesa

Potrero

Butte

Plateau

Terrace

Table

Table hill

Table-topped hill

Table mountain

Tableland

Earth's landforms
Mountainous
Continental plain
Fluvial
Glacial
Oceanic and
coastal landforms
Volcanic
Aeolian
Artificial

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