A flood is an overflow of water that submerges land which is usually dry. The European Union Floods Directive defines a flood as a covering by water of land not normally covered by water, in the sense of flowing water, the word may be applied to the inflow of the tide. Floods can occur in rivers when the flow exceeds the capacity of the river channel. Floods often cause damage to homes and businesses if they are in the flood plains of rivers. Some floods develop slowly, while others such as floods, can develop in just a few minutes. Additionally, floods can be local, impacting a neighborhood or community, or very large, the word flood comes from the Old English flod, a word common to Germanic languages. Deluge myths are stories of a great flood sent by a deity or deities to destroy civilization as an act of divine retribution. Floods can happen on flat or low-lying areas when water is supplied by rainfall or snowmelt more rapidly than it can infiltrate or run off. The excess accumulates in place, sometimes to hazardous depths, surface soil can become saturated, which effectively stops infiltration, where the water table is shallow, such as a floodplain, or from intense rain from one or a series of storms.
Infiltration is slow to negligible through frozen ground, concrete, areal flooding begins in flat areas like floodplains and in local depressions not connected to a stream channel, because the velocity of overland flow depends on the surface slope. Endorheic basins may experience flooding during periods when precipitation exceeds evaporation. Floods occur in all types of river and stream channels, from the smallest ephemeral streams in humid zones to normally-dry channels in arid climates to the worlds largest rivers. When overland flow occurs on tilled fields, it can result in a flood where sediments are picked up by run off. Localized flooding may be caused or exacerbated by drainage obstructions such as landslides, debris, slow-rising floods most commonly occur in large rivers with large catchment areas. The increase in flow may be the result of sustained rainfall, rapid snow melt, the cause may be localized convective precipitation or sudden release from an upstream impoundment created behind a dam, landslide, or glacier.
In one instance, a flood killed eight people enjoying the water on a Sunday afternoon at a popular waterfall in a narrow canyon. Without any observed rainfall, the rate increased from about 50 to 1,500 cubic feet per second in just one minute. Two larger floods occurred at the site within a week
Corfu is a Greek island in the Ionian Sea. It is the second largest of the Ionian Islands, including its satellite islands. The island is part of the Corfu regional unit, and is administered as a single municipality, the municipality has an area of 610.936 km2, the island proper 592.877 km2. The principal city of the island and seat of the municipality is named Corfu, Corfu is home to the Ionian University. The island is bound up with the history of Greece from the beginnings of Greek mythology and its history is full of battles and conquests. Castles punctuating strategic locations across the island are a legacy of these struggles, two of these castles enclose its capital, which is the only city in Greece to be surrounded in such a way. As a result, Corfus capital has been declared a Kastropolis by the Greek government. From medieval times and into the 17th century, the island was recognised as a bulwark of the European States against the Ottoman Empire, the fortifications of the island were used by the Venetians to defend against Ottoman intrusion into the Adriatic.
Corfu repulsed several Ottoman sieges, before falling under British rule following the Napoleonic Wars, in 2007, the citys old quarter was added to the UNESCO World Heritage List, following a recommendation by ICOMOS. Corfu is a popular tourist destination. The island was the location of the 1994 European Union summit, the Greek name, Kerkyra or Korkyra, is related to two powerful water deities, god of the sea, and Asopos, an important Greek mainland river. According to myth, Poseidon fell in love with the beautiful nymph Korkyra, daughter of Asopos and river nymph Metope, Poseidon brought Korkyra to the hitherto unnamed island and, in marital bliss, offered her name to the place, which gradually evolved to Kerkyra. They had a child they called Phaiax, after whom the inhabitants of the island were named Phaiakes, Corfus nickname is the island of the Phaeacians. The name Corfù, an Italian version of the Byzantine Κορυφώ, meaning city of the peaks, derives from the Byzantine Greek Κορυφαί, the northeastern edge of Corfu lies off the coast of Sarandë, separated by straits varying in width from 3 to 23 km.
The southeast side of the island lies off the coast of Thesprotia and its shape resembles a sickle, to which it was compared by the ancients, the concave side, with the city and harbour of Corfu in the centre, lies toward the Albanian coast. With the islands area estimated at 592.9 square kilometres, it runs approximately 64 km long, two high and well-defined ranges divide the island into three districts, of which the northern is mountainous, the central undulating, and the southern low-lying. The more important of the two ranges, that of Pantokrator stretches east and west from Cape Falacro to Cape Psaromita, and attains its greatest elevation in the summit of the same name. The second range culminates in the mountain of Santi Jeca, or Santa Decca, as it is called by misinterpretation of the Greek designation Άγιοι Δέκα, or the Ten Saints
Bay mud manifests low shear strength, high compressibility and low permeability, making it hazardous to build upon in seismically active regions like the San Francisco Bay Area. Typical bulk density of bay mud is approximately 1.3 grams per cubic centimetre, Bay mud has its own official geological abbreviation. The designation for Quaternary older bay mud is Qobm and the acronym for Quaternary younger bay mud is Qybm, an alluvial layer is often found overlying the older bay mud. In relation to shipping channels, it is necessary to dredge bay bottoms. It is not uncommon to dredge the same channel repeatedly since further settling sediments are prone to redeposit on an open valley floor. Bay muds originate from two generalized sources, first alluvial deposits of clays and sand occur from streams tributary to a given bay. The extent of these unconsolidated interglacial deposits typically ranges throughout a given bay to the extent of the historical perimeter marshlands, second, in periods of high glaciation, deposits of silts and organic plus inorganic detritus may form a separate distinct layer.
Thus bay muds are important time records of activity and streamflow throughout the Quaternary period. Some depositional formation is quite recent, such as in the case of Florida Bay, where much of the bay mud has accumulated since 2000 BC, and consists of primarily decayed organic material. In the case of the Bristol Channel in the United Kingdom bay, mud formation has been occurring at least since the Eemian Stage, in other cases such as with San Francisco Bay, deposition has been interrupted by sea-level changes, and strata of vastly different vintages are found. In the San Francisco Bay Area, these are called Young bay mud, human activities can affect deposition, close to half of the Young Bay Mud in San Francisco Bay was placed in the period 1855–1865, as a result of placer mining in the Sierra Nevada foothills. Construction on bay mud sites is difficult because of the low strength. A number of buildings have been constructed over bay muds, typically employing special mitigation designs to withstand seismic risks.
Complicating design issues, fill is sometimes deposited on the surface level. For example, the Dakin Building in Brisbane, California was designed in 1985 to sit on piles 150 feet deep, anchoring to the Franciscan formation, below the bay muds and through an upper fill layer. Furthermore, the entrance ramp has been set on a giant hinge to allow the surrounding land to settle, while the building absolute height remains constant. The Crowne Plaza high-rise hotel in Burlingame, California was designed to sit over bay muds, as was the Westin Hotel in Millbrae, indeed, Bostons entire Back Bay district is named for the tidal bay that it now covers. Logan International Airport and the San Francisco International Airport are constructed over bay mud, when the mud layer is exposed at the tidal fringe, mudflats result affording a unique ecotone that affords numerous shorebird species a safe feeding and resting habitat
The English Channel, called simply the Channel, is the body of water that separates southern England from northern France, and links the southern part of the North Sea to the Atlantic Ocean. It is about 560 km long and varies in width from 240 km at its widest to 33.3 km in the Strait of Dover and it is the smallest of the shallow seas around the continental shelf of Europe, covering an area of some 75,000 km2. The International Hydrographic Organization defines the limits of the English Channel as follows, a line joining Isle Vierge to Lands End. The southwestern limit of the North Sea, the IHO defines the southwestern limit of the North Sea as a line joining the Walde Lighthouse and Leathercoat Point. The Walde Lighthouse is 6 km east of Calais, and Leathercoat Point is at the end of St Margarets Bay. The Strait of Dover, at the Channels eastern end, is its narrowest point and it is relatively shallow, with an average depth of about 120 m at its widest part, reducing to a depth of about 45 m between Dover and Calais.
Eastwards from there the adjoining North Sea reduces to about 26 m in the Broad Fourteens where it lies over the watershed of the land bridge between East Anglia and the Low Countries. It reaches a depth of 180 m in the submerged valley of Hurds Deep,48 km west-northwest of Guernsey. The eastern region along the French coast between Cherbourg and the mouth of the Seine river at Le Havre is frequently referred to as the Bay of the Seine. There are several islands in the Channel, the most notable being the Isle of Wight off the English coast. The coastline, particularly on the French shore, is indented, several small islands close to the coastline, including Chausey. The Cotentin Peninsula in France juts out into the Channel, whilst on the English side there is a parallel channel known as the Solent between the Isle of Wight and the mainland. The Celtic Sea is to the west of the Channel, the time difference of about six hours between high water at the eastern and western limits of the Channel is indicative of the tidal range being amplified further by resonance.
It was never defined as a border and the names were more or less descriptive. It was not considered as the property of a nation, before the development of the modern nations, British scholars very often referred to it as Gaulish and the French one as British or English. The name English Channel has been used since the early 18th century. In modern Dutch, however, it is known as Het Kanaal, later, it has been known as the British Channel or the British Sea having been called the Oceanus Britannicus by the 2nd-century geographer Ptolemy. The same name is used on an Italian map of about 1450, the Anglo-Saxon texts often call it Sūð-sǣ as opposed to Norð-sǣ
Dredging is an excavation activity usually carried out underwater, in shallow seas or freshwater areas with the purpose of gathering up bottom sediments and disposing of them at a different location. This technique is used to keep waterways navigable. It is used as a way to replenish sand on some public beaches, fishing dredges are used as a technique for catching certain species of edible clams and crabs. Capital, dredging carried out to create a new harbor, berth or waterway, preparatory and excavation for future bridges, piers or docks/wharves, often connected with foundation work. This is often carried out with a trailing suction hopper dredge, most dredging is for this purpose, and it may be done to maintain the holding capacity of reservoirs or lakes. Land reclamation, dredging to mine sand, clay or rock from the seabed and this is typically performed by a cutter-suction dredge or trailing suction hopper dredge. The material may be used for flood or erosion control, beach nourishment, mining sand offshore and placing on a beach to replace sand eroded by storms or wave action.
This is done to enhance the recreational and protective function of the beaches and this is typically performed by a cutter-suction dredge or trailing suction hopper dredge. Harvesting materials, dredging sediment for elements like gold, diamonds or other valuable trace substances, seabed mining, a possible future use, recovering natural metal ore nodules from the seas abyssal plains. Construction materials, dredging sand and gravels from offshore licensed areas for use in construction industry, very specialist industry focused in NW Europe using specialized trailing suction hopper dredgers self discharging dry cargo ashore. Anti-eutrophication, Dredging is an option for the remediation of eutrophied water bodies. Contaminant remediation, to areas affected by chemical spills, storm water surges. Disposal becomes a large factor in these operations. Removing trash and debris, often done in combination with maintenance dredging, flood prevention, this can help to increase channel depth and therefore increase a channels capacity for carrying water.
This tradition has now more or less obsolete and the tools used to do this have changed significantly. Oyster dredging or harvesting, in Louisiana and other states with salt water estuaries that can sustain bottom oyster beds. A heavy metal rectangular scoop device is towed astern of a boat with a chain bridle attached to a cable. The device is periodically hauled aboard and the oysters in it are sorted and bagged for shipment to a processing facility
A meander, in general, is a bend in a sinuous watercourse or river. A meander forms when moving water in a stream erodes the outer banks and widens its valley, a stream of any volume may assume a meandering course, alternately eroding sediments from the outside of a bend and depositing them on the inside. The result is a pattern as the stream meanders back. When a meander gets cut off from the stream, an oxbow lake forms. Over time meanders migrate downstream, sometimes in such a time as to create civil engineering problems for local municipalities attempting to maintain stable roads. There is not yet full consistency or standardization of scientific terminology used to describe watercourses, a variety of symbols and schemes exist. Parameters based on mathematical formulae or numerical data vary as well, unless otherwise defined in a specific scheme meandering and sinuosity here are synonymous and mean any repetitious pattern of bends, or waveforms. In some schemes, meandering applies only to rivers with exaggerated circular loops or secondary meanders, sinuosity is one of the channel types that a stream may assume over all or part of its course.
All streams are sinuous at some time in their history over some part of their length. The term derives from the Meander River located in present-day Turkey and known to the Ancient Greeks as Μαίανδρος Maiandros and its course is so exceedingly winding that everything winding is called meandering. The Meander River is located south of Izmir, east of the ancient Greek town of Miletus, Milet and it flows through a graben in the Menderes Massif, but has a flood plain much wider than the meander zone in its lower reach. Its modern Turkish name is the Büyük Menderes River, when a fluid is introduced to an initially straight channel which bends, the sidewalls induce a pressure gradient that causes the fluid to alter course and follow the bend. From here, two opposing processes occur, irrotational flow and secondary flow, for a river to meander, secondary flow must dominate. Irrotational flow, From Bernoullis equations, high pressure results in low velocity, therefore, in the absence of secondary flow we would expect low fluid velocity at the outside bend and high fluid velocity at the inside bend.
This classic fluid mechanics result is irrotational vortex flow, in the context of meandering rivers, its effects are dominated by those of secondary flow. Secondary flow, A force balance exists between pressure forces pointing to the bend of the river and centrifugal forces pointing to the outside bend of the river. In the context of meandering rivers, a boundary layer exists within the layer of fluid that interacts with the river bed. Inside that layer and following standard boundary-layer theory, the velocity of the fluid is effectively zero, centrifugal force, which depends on velocity, is therefore effectively zero
Surface runoff is the flow of water that occurs when excess stormwater, meltwater, or other sources flows over the Earths surface. Surface runoff is a component of the water cycle. It is the agent in soil erosion by water. Runoff that occurs on the surface before reaching a channel is called a nonpoint source. If a nonpoint source contains man-made contaminants, or natural forms of pollution the runoff is called nonpoint source pollution, a land area which produces runoff that drains to a common point is called a drainage basin. When runoff flows along the ground, it can pick up soil contaminants including petroleum, surface runoff can be generated either by rainfall, snowfall or by the melting of snow, or glaciers. Snow and glacier melt occur only in areas cold enough for these to form permanently, typically snowmelt will peak in the spring and glacier melt in the summer, leading to pronounced flow maxima in rivers affected by them. The determining factor of the rate of melting of snow or glaciers is both air temperature and the duration of sunlight, in high mountain regions, streams frequently rise on sunny days and fall on cloudy ones for this reason.
In areas where there is no snow, runoff will come from rainfall, not all rainfall will produce runoff because storage from soils can absorb light showers. This occurs when the rate of rainfall on a surface exceeds the rate at which water can infiltrate the ground and this is called flooding excess overland flow, Hortonian overland flow, or unsaturated overland flow. This more commonly occurs in arid and semi-arid regions, where rainfall intensities are high and this occurs largely in city areas where pavements prevent water from flooding. When the soil is saturated and the depression storage filled, and rain continues to fall, the level of antecedent soil moisture is one factor affecting the time until soil becomes saturated. This runoff is called saturation excess overland flow or saturated overland flow, soil retains a degree of moisture after a rainfall. This residual water moisture affects the soils infiltration capacity, during the next rainfall event, the infiltration capacity will cause the soil to be saturated at a different rate.
The higher the level of antecedent soil moisture, the more quickly the soil becomes saturated, once the soil is saturated, runoff occurs. After water infiltrates the soil on a portion of a hill, the water may flow laterally through the soil. This is called subsurface return flow or throughflow, any remaining surface water eventually flows into a receiving water body such as a river, estuary or ocean. Urbanization increases surface runoff by creating more impervious surfaces such as pavement and it is instead forced directly into streams or storm water runoff drains, where erosion and siltation can be major problems, even when flooding is not
St. Johns River
The St. Johns River is the longest river in the U. S. state of Florida and its most significant one for commercial and recreational use. At 310 miles long, it winds through or borders twelve counties, three of which are the states largest. The drop in elevation from headwaters to mouth is less than 30 feet, like most Florida waterways and it is notable among some that the rivers course flows north, a relatively rare characteristic. Numerous lakes are formed by the river or flow into it, the narrowest point is in the headwaters, an unnavigable marsh in Indian River County. The St. Johns drainage basin of 8,840 square miles includes some of Floridas major wetlands and it is separated into three major basins and two associated watersheds for Lake George and the Ocklawaha River, all managed by the St. Johns River Water Management District. It has been the subject of William Bartrams journals, Marjorie Kinnan Rawlings books, when attention was turned to the state, much of the land was rapidly overdeveloped in a national zeal for progress.
The St. Johns, like many Florida rivers, was altered to make way for agricultural and residential centers and it suffered severe pollution and human interference that has diminished the natural order of life in and around the river. In all,3.5 million people live within the watersheds that feed into the St. Johns River. The St. Johns, named one of 14 American Heritage Rivers in 1998, was included on a list of Americas Ten Most Endangered Rivers in 2008. Restoration efforts are under way for the basins around the St. Johns as Florida continues to deal with population increases in the rivers vicinity, starting in Indian River County and meeting the Atlantic Ocean at Duval County, the St. Johns is Floridas primary commercial and recreational waterway. It flows north from its headwaters, originating in the direction of the Lake Wales Ridge, because of this low elevation drop, the river has a long backwater. It ebbs and flows with tides that pass through the barrier islands, uniquely, it shares the same regional terrain as the parallel Kissimmee River, although the Kissimmee flows south.
The St. Johns River is separated into three basins and two associated watersheds managed by the St. Johns River Water Management District, because the river flows in a northerly direction, the upper basin is located in the headwaters of the river at its southernmost point. Indian River County is where the river begins as a network of marshes, the St. Johns River is a blackwater stream, meaning that it is fed primarily by swamps and marshes lying beneath it, water seeps through the sandy soil and collects in a slight valley. The upper basin measures approximately 2,000 square miles, the St. Johns transforms into a waterway in Brevard County. The river touches on the borders of Osceola and Orange Counties, the upper basin of the St. Johns was significantly lowered in the 1920s with the establishment of the Melbourne Tillman drainage project. This drained the St. Johns headwaters eastward to the Indian River through canals dug across the Ten-Mile Ridge near Palm Bay, as of 2015, these past diversions are being partially reversed through the first phase of the Canal 1 Rediversion project.
The river is at its narrowest and most unpredictable in this basin, channel flows are not apparent and are usually unmarked
Black Canyon of the Gunnison National Park
Black Canyon of the Gunnison National Park is a United States National Park located in western Colorado and managed by the National Park Service. There are two entrances to the park, the south rim entrance is located 15 miles east of Montrose. The park contains 12 miles of the 48-mile long Black Canyon of the Gunnison River, the canyons name owes itself to the fact that parts of the gorge only receive 33 minutes of sunlight a day, according to Images of America, The Black Canyon of the Gunnison. The Gunnison River drops an average of 34 feet per mile through the entire canyon, by comparison, the Colorado River drops an average of 7.5 feet per mile through the Grand Canyon. The greatest descent of the Gunnison River occurs within the park at Chasm View dropping 240 feet per mile, the Black Canyon is so named because its steepness makes it difficult for sunlight to penetrate into its depths. As a result, the canyon is often shrouded in shadow, at its narrowest point the canyon is only 40 ft wide at the river.
The extreme steepness and depth of the Black Canyon formed as the result of geologic processes acting together. The Gunnison River is primarily responsible for carving the canyon, though several other events had to occur in order to form the canyon as it is seen today. The lighter-colored pegmatite dikes that can be seen crosscutting the basement rocks formed during this same period, the entire area underwent uplift during the Laramide orogeny between 70 and 40 million years ago which was part of the Gunnison Uplift. This raised the Precambrian gneiss and schist that makes up the canyon walls, during the Tertiary from 26 to 35 million years ago large episodes of volcanism occurred in the area immediately surrounding the present day Black Canyon. The West Elk Mountains, La Sal Mountains, Henry Mountains, with the Gunnison River’s course set, a broad uplift in the area 2 to 3 million years ago caused the river to cut through the softer volcanic deposits. Eventually the river reached the Precambrian rocks of the Gunnison Uplift, since the river was unable to change its course, it began scouring through the extremely hard metamorphic rocks of the Gunnison Uplift.
The river’s flow was much larger than currently, with higher levels of turbidity. As a result, the river dug down through the Precambrian gneiss, the extreme hardness of the metamorphic rock along with the relative quickness with which the river carved through them created the steep walls that can be seen today. A number of canyons running into the Black Canyon slope in the wrong direction for water to flow into the canyon. It is believed that streams in the region shifted to a more north-flowing drainage pattern in response to a change in the tilt of the surrounding terrain. The west-flowing Gunnison, was trapped in the hard Precambrian rock of the Black Canyon. The Ute Indians had known the canyon to exist for a time before the first Europeans saw it
Lava is the molten rock expelled by a volcano during an eruption. The resulting rock after solidification and cooling is called lava. The molten rock is formed in the interior of planets, including Earth. The source of the heat melts the rock within the earth is geothermal energy. When first erupted from a vent, lava is a liquid usually at temperatures from 700 to 1,200 °C. A lava flow is an outpouring of lava, which is created during a non-explosive effusive eruption. When it has stopped moving, lava solidifies to form igneous rock, the term lava flow is commonly shortened to lava. Although lava can be up to 100,000 times more viscous than water, lava can flow great distances before cooling and solidifying because of its thixotropic, explosive eruptions produce a mixture of volcanic ash and other fragments called tephra, rather than lava flows. The word lava comes from Italian, and is derived from the Latin word labes which means a fall or slide. The first use in connection with extruded magma was apparently in an account written by Francesco Serao on the eruption of Vesuvius between May 14 and June 4,1737.
Serao described a flow of lava as an analogy to the flow of water. The composition of almost all lava of the Earths crust is dominated by silicate minerals, mostly feldspars, pyroxenes, micas, igneous rocks, which form lava flows when erupted, can be classified into three chemical types, felsic and mafic. These classes are primarily chemical, the chemistry of lava tends to correlate with the temperature, its viscosity. Felsic or silicic lavas such as rhyolite and dacite typically form lava spines, most silicic lava flows are extremely viscous, and typically fragment as they extrude, producing blocky autobreccias. Felsic magmas can erupt at temperatures as low as 650 to 750 °C, unusually hot rhyolite lavas, may flow for distances of many tens of kilometres, such as in the Snake River Plain of the northwestern United States. Intermediate or andesitic lavas are lower in aluminium and silica, and usually somewhat richer in magnesium, intermediate lavas form andesite domes and block lavas, and may occur on steep composite volcanoes, such as in the Andes.
Poorer in aluminium and silica than felsic lavas, and commonly hotter, greater temperatures tend to destroy polymerized bonds within the magma, promoting more fluid behaviour and a greater tendency to form phenocrysts. Higher iron and magnesium tends to manifest as a darker groundmass, mafic or basaltic lavas are typified by their high ferromagnesian content, and generally erupt at temperatures in excess of 950 °C
A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, lake or another river. In some cases a river flows into the ground and becomes dry at the end of its course without reaching another body of water, small rivers can be referred to using names such as stream, brook and rill. There are no official definitions for the term river as applied to geographic features. Many names for small rivers are specific to geographic location, examples are run in parts of the United States, burn in Scotland and northeast England. Sometimes a river is defined as being larger than a creek, but not always, Rivers are part of the hydrological cycle. Potamology is the study of rivers while limnology is the study of inland waters in general. Extraterrestrial rivers of liquid hydrocarbons have recently found on Titan. Channels may indicate past rivers on other planets, specifically outflow channels on Mars and rivers are theorised to exist on planets, a river begins at a source, follows a path called a course, and ends at a mouth or mouths.
The water in a river is confined to a channel. In larger rivers there is a wider floodplain shaped by flood-waters over-topping the channel. Floodplains may be wide in relation to the size of the river channel. This distinction between river channel and floodplain can be blurred, especially in areas where the floodplain of a river channel can become greatly developed by housing. Rivers can flow down mountains, through valleys or along plains, the term upriver refers to the direction towards the source of the river, i. e. against the direction of flow. Likewise, the term describes the direction towards the mouth of the river. The term left bank refers to the bank in the direction of flow. The river channel typically contains a stream of water, but some rivers flow as several interconnecting streams of water. Extensive braided rivers are now found in only a few regions worldwide and they occur on peneplains and some of the larger river deltas. Anastamosing rivers are similar to braided rivers and are quite rare
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, landforms are categorized by characteristic physical attributes such as elevation, orientation, rock exposure, and soil type. 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, saddles and backslopes. Some generic landform elements including, peaks, ridges, pools, Terrain is the third or vertical dimension of land surface. Topography is the study of terrain, although the word is 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. Elementary landforms are the smallest homogeneous divisions of the land surface and 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, 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, landforms do not include man-made features, such as canals and many harbors, and geographic features, such as deserts and grasslands.
Many of the terms are not restricted to refer to features of the planet Earth, examples are mountains, polar caps, and valleys, which are found on all of the terrestrial planets. The scientific study of landforms is known as geomorphology, 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. Until recently, compiling the data found in data sets required time consuming. The most detailed DEMs available are measured directly using LIDAR techniques, geomorphology Land List of landforms Open-geomorphometry project Terrain Open-Geomorphometry Project