The sun, which drives the water cycle, heats water in oceans and seas.
Water evaporates as water vapor into the air. Ice and snow can sublimate directly into water vapor. Evapotranspiration is water transpired from plants and evaporated from the soil. Rising air currents take the vapor up into the atmosphere where cooler temperatures cause it to condense into clouds.
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Air currents move water vapor around the globe, cloud particles collide, grow, and fall out of the sky as precipitation. Some precipitation falls as snow or hail, and can accumulate as ice caps and glaciers, which can store frozen water for thousands of years. Snowpacks can thaw and melt, and the melted water flows over land as snowmelt. Most water falls back into the oceans or onto land as rain, where the water flows over the ground as surface runoff. A portion of runoff enters rivers in valleys in the landscape, with streamflow moving water towards the oceans. Runoff and groundwater are stored as freshwater in lakes.
Not all runoff flows into rivers, much of it soaks into the ground as infiltration. Some water infiltrates deep into the ground and replenishes aquifers, which store freshwater for long periods of time. Some infiltration stays close to the land surface and can seep back into surface-water bodies (and the ocean) as groundwater discharge. Some groundwater finds openings in the land surface and comes out as freshwater springs. Over time, the water returns to the ocean, where our water cycle started.
Different Processes of the Hydrologic Cycle
Precipitation – Condensed water vapor that falls to the Earth’s surface . Most precipitation occurs as;rain, but also includes;snow,;hail,;fog drip,;graupel, and;sleetSnowmelt -;The runoff produced by melting snow.Runoff-;The variety of ways by which water moves across the land.
This includes both;surface runoff;and;channel runoff. As it flows, the water may seep into the ground, evaporate into the air, become stored in lakes or reservoirs, or be extracted for agricultural or other human uses.
Infiltration -;The flow of water from the ground surface into the ground. Once infiltrated, the water becomes;soil moisture;or;groundwater.Evaporation –The transformation of water from liquid to gas phases as it moves from the ground or bodies of water into the overlying atmosphere.Sublimation -;The state change directly from solid water (snow or ice) to water vapor.
Advection -;The movement of water;; in solid, liquid, or vapor states;; through the atmosphere. Without advection, water that evaporated over the oceans could not precipitate over land.Condensation -;The transformation of water vapor to liquid water droplets in the air, creating;clouds;and;fog.transpiration -;The release of water vapor from plants and soil into the air. Water vapor is a gas that cannot be seen.
Evapotranspiration;(ET) is a term used to describe the sum of;evaporation;and;plant;transpiration;from the Earth’s land surface to atmosphere. Evaporation accounts for the movement of water to the air from sources such as the soil, canopy interception, and waterbodies. Transpiration accounts for the movement of water within a plant and the subsequent loss of water as vapor through stomata in its leaves.
Evapotranspiration is an important part of the water cycle. An element (such as a tree) that contributes to evapotranspiration can be called an evapotranspirator.
Evapotransporation and Water Cycle
Evapotranspiration is a significant water loss from drainage basins. Types of vegetation and land use significantly affect evapotranspiration, and therefore the amount of water leaving a drainage basin. Because water transpired through leaves comes from the roots, plants with deep reaching roots can more constantly transpire water. Herbaceous plants generally transpire less than woody plants because they usually have less extensive foliage. Conifer forests tend to have higher rates of evapotranspiration than deciduous forests, particularly in the dormant and early spring seasons.
This is primarily due to the enhanced amount of precipitation intercepted and evaporated by conifer foliage during these periods . Factors that affect evapotranspiration include the plant’s growth stage or level of maturity, percentage of soil cover, solar radiation, humidity, temperature, and wind.Through evapotranspiration, forests reduce water yield, except in unique ecosystems called cloud forests. Trees in cloud forests condense fog or low clouds into liquid water on their surface, which drips down to the ground. These trees still contribute to evapotranspiration, but often condense more water than they evaporate or transpire.In areas that are not irrigated, actual evapotranspiration is usually no greater than precipitation, with some buffer in time depending on the soil’s ability to hold water. It will usually be less because some water will be lost due to percolation or surface runoff.
An exception is areas with high water tables, where capillary action can cause water from the groundwater to rise through the soil matrix to the surface. If potential evapotranspiration is greater than actual precipitation, then soil will dry out, unless irrigation is used.
Field capacity is the amount of soil moisture or water content held in soil after excess water has drained away and the rate of downward movement has materially decreased, which usually takes place within 2–3 days after a rain or irrigation in pervious soils of uniform structure and texture. The physical definition of field capacity (expressed symbolically as ?fc) is the bulk water content retained in soil at ?33 J/kg (or ?0.33 bar) of hydraulic head or suction pressure. The term originated from Israelson and West and Frank Veihmeyer and Arthur Hendrickson.
Permanent wilting point (PWP) or wilting point (WP) is defined as the minimal point of soil moisture the plant requires not to wilt. If moisture decreases to this or any lower point a plant wilts and can no longer recover its turgidity when placed in a saturated atmosphere for 12 hours.
The physical definition of the wilting point (symbolically expressed as ?pwp or ?wp) is defined as the water content at ?1500 J/kg (or ?15 bars) of suction pressure, or negative hydraulic head.
An aquifer is a wet underground layer of water-bearing permeable rock or unconsolidated materials (gravel, sand, silt, or clay) from which groundwater can be usefully extracted using a water well. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology. Related terms include aquitard, which is a bed of low permeability along an aquifer, and aquiclude (or aquifuge), which is a solid, impermeable area underlying or overlying an aquifer. If the impermeable area overlies the aquifer pressure could cause it to become a confined aquifer.
Aquifers Groundwater in Rock Formations
Groundwater may exist in underground rivers (e.g., caves where water flows freely underground).
This may occur in eroded limestone areas known as karst topography, which make up only a small percentage of Earth’s area. More usual is that the pore spaces of rocks in the subsurface are simply saturated with water — like a kitchen sponge — which can be pumped out for agricultural, industrial, or municipal uses.If a rock unit of low porosity is highly fractured, it can also make a good aquifer (via fissure flow), provided the rock has an appreciable hydraulic conductivity to facilitate movement of water. Porosity is important, but, alone, it does not determine a rock’s ability of being an aquifer. Areas of the Deccan Traps (a basaltic lava) in west central India are good examples of rock formations with high porosity but low permeability, which makes them poor aquifers. Similarly, the micro-porous (Upper Cretaceous) Chalk of south east England, although having a reasonably high porosity, has a low grain-to-grain permeability, with much of its good water-yielding characteristics being due to micro-fracturing and fissuring.
Fresh-water aquifers, especially those with limited recharge by meteoric water, can be over-exploited and, depending on the local hydrogeology, may draw in non-potable water or saltwater (saltwater intrusion) from hydraulically connected aquifers or surface water bodies.
This can be a serious problem, especially in coastal areas and other areas where aquifer pumping is excessive. In some areas, the ground water can be contaminated by mineral poisons, such as arsenic – see Arsenic contamination of groundwater.
Aquifer Dependence 2
Municipal, irrigation, and industrial water supplies are provided through large wells. Multiple wells for one water supply source are termed “wellfields”, which may withdraw water from confined or unconfined aquifers. Using ground water from deep, confined aquifers provides more protection from surface water contamination. Some wells, termed “collector wells,” are specifically designed to induce infiltration of surface (usually river) water.
Aquifer drawdown or overdrafting and the pumping of fossil water increases the total amount of water in the hydrosphere that is subject to transpiration and evaporation thereby causing accretion in water vapour and cloud cover which are the primary absorbers of infrared radiation in the earth’s atmosphere. Adding water to the system has a forcing effect on the whole earth system, an accurate estimate of which hydrogeological fact is yet to be quantified.
a solid, impermeable area underlying or overlying an aquifer.
The water table is the level at which the submarine pressure is far from atmospheric pressure. It may be conveniently visualized as the ‘surface’ of the subsurface materials that are saturated with groundwater in a given vicinity. However, saturated conditions may extend above the water table as surface tension holds water in some pores below atmospheric pressure. individual points on the water table are typically measured as the elevation that the water rises to in a well screened in the shallow groundwater.
A graben is the result of a block of land being downthrown producing a valley with a distinct scarp on each side.
Graben often occur side-by-side with horsts. Horst and graben structures are indicative of tensional forces and crustal stretching.
the raised fault block bounded by normal faults or graben. A horst is formed from extension of the Earth’s crust. The raised block is a portion of the crust that generally remains stationary or is uplifted while the land has dropped on either side.
Angle of Repose
is the steepest angle of descent or dip of the slope relative to the horizontal plane when material on the slope face is on the verge of sliding.When bulk granular materials are poured onto a horizontal surface, a conical pile will form. The internal angle between the surface of the pile and the horizontal surface is known as the angle of repose and is related to the density, surface area and shapes of the particles, and the coefficient of friction of the material.
Material with a low angle of repose forms flatter piles than material with a high angle of repose.It is also commonly used by mountaineers as a factor in analyzing avalanche danger in mountainous areas.
the lowest point to which it can flow, often referred to as the ‘mouth’ of the river. For large rivers, sea level is usually the base level, but a large river or lake is likewise the base level for tributary streams. All rivers and streams erode toward sea level, which is also known as the “ultimate base level.
” If a river is dammed, a new base level (the level of the reservoir) replaces the ultimate base level. As a result, the stream’s base level is raised. Consequently, this reduces the stream’s velocity, leads to deposition, and a reduction of the gradient upstream from the reservoir.
Base level is also significant for subsurface drainage. A low base level is a prerequisite for the formation of karst topography, a network of sinkholes and caverns that can develop as slightly acidic groundwater enlarges joints (by solution) in limestone rock. Often this network of underground drainage feeds back to surface drainage along the edges of larger rivers, which are the effective base level.
Base level 2
When the source of a stream is very high relative to its base level (high stream gradient), erosion proceeds rapidly due to the energy of the rapidly moving water and the topography becomes rugged, and it is considered a young stream (geologically speaking). When erosion has acted for a long geologic time, wearing down the high points and making a small difference between the source and the base level of a stream (low stream gradient), then the stream is called mature. Mature stream valleys have gentle slopes, rounded higher points and meandering courses.
Chemical weathering changes the composition of rocks, often transforming them when water interacts with minerals to create various chemical reactions. Chemical weathering is a gradual and ongoing process as the mineralogy of the rock adjusts to the near surface environment.
New or secondary minerals develop from the original minerals of the rock. In this the processes of oxidation and hydrolysis are most important.
Chemical Weathering TypesDissolution – Carbonation
Rainfall is acidic because atmospheric carbon dioxide dissolves in the rainwater producing weak carbonic acid. In unpolluted environments, the rainfall pH is around 5.6. Acid rain occurs when gases such as sulfur dioxide and nitrogen oxides are present in the atmosphere. These oxides react in the rain water to produce stronger acids and can lower the pH to 4.5 or even 3.
0. Sulfur dioxide, SO2, comes from volcanic eruptions or from fossil fuels, can become sulfuric acid within rainwater, which can cause solution weathering to the rocks on which it falls.Some minerals, due to their natural solubility (e.
g. evaporites), oxidation potential (iron-rich minerals, such as pyrite), or instability relative to surficial conditions will weather through dissolution naturally, even without acidic water.One of the most well-known solution weathering processes is carbonation, the process in which atmospheric carbon dioxide leads to solution weathering. Carbonation occurs on rocks which contain calcium carbonate, such as limestone and chalk. This takes place when rain combines with carbon dioxide or an organic acid to form a weak carbonic acid which reacts with calcium carbonate (the limestone) and forms calcium bicarbonate. This process speeds up with a decrease in temperature, not because low temperatures generally drive reactions faster, but because colder water holds more dissolved carbon dioxide gas. Carbonation is therefore a large feature of glacial weathering.
Chemical Weathering TypesMineral HydrationHydrolysis on Silicates and Carbonates
Mineral hydration is a form of chemical weathering that involves the rigid attachment of H+ and OH- ions to the atoms and molecules of a mineral.When rock minerals take up water, the increased volume creates physical stresses within the rock. For example iron oxides are converted to iron hydroxides and the hydration of anhydrite forms gypsum.Hydrolysis is a chemical weathering process affecting silicate and carbonate minerals. In such reactions, pure water ionizes slightly and reacts with silicate minerals.
Chemical Weathering Oxidation
Within the weathering environment chemical oxidation of a variety of metals occurs. The most commonly observed is the oxidation of Fe2+ (iron) and combination with oxygen and water to form Fe3+ hydroxides and oxides such as goethite, limonite, and hematite.
This gives the affected rocks a reddish-brown coloration on the surface which crumbles easily and weakens the rock. This process is better known as ‘rusting’, though it is distinct from the rusting of metallic iron. Many other metallic ores and minerals oxidize and hydrate to produce colored deposits, such as chalcopyrites or CuFeS2 oxidizing to copper hydroxide and iron oxides.
Chemical Weathering TypeBiological
A number of plants and animals may create chemical weathering through release of acidic compounds, i.e. moss on roofs is classed as weathering. Mineral weathering can also be initiated and/or accelerated by soil microorganisms.The most common forms of biological weathering are the release of chelating compounds (i.
e. organic acids, siderophores) and of acidifying molecules (i.e. protons, organic acids) by plants so as to break down aluminium and iron containing compounds in the soils beneath them. Decaying remains of dead plants in soil may form organic acids which, when dissolved in water, cause chemical weathering
Physical weathering involves the breakdown of rocks and soils through direct contact with atmospheric conditions, such as heat, water, ice and pressurePhysical weathering is the class of processes that causes the disintegration of rocks without chemical change.
The primary process in physical weathering is abrasion (the process by which clasts and other particles are reduced in size). However, chemical and physical weathering often go hand in hand. For example, cracks exploited by physical weathering will increase the surface area exposed to chemical action.
Furthermore, the chemical action at minerals in cracks can aid the disintegration process.
Physical Weathering TypesThermal
Thermal stress weathering (sometimes called insolation weathering) results from expansion or contraction of rock, caused by temperature changes. Thermal stress weathering comprises two main types, thermal shock and thermal fatigue. Thermal stress weathering is an important mechanism in deserts, where there is a large diurnal temperature range, hot in the day and cold at night. The repeated heating and cooling exerts stress on the outer layers of rocks, which can cause their outer layers to peel off in thin sheets. Although temperature changes are the principal driver, moisture can enhance thermal expansion in rock.
Forest fires and range fires are also known to cause significant weathering of rocks and boulders exposed along the ground surface. Intense, localized heat can rapidly expand a boulder.
Physical Weathering TypesFrost Weathering
This processes include frost shattering, frost-wedging and freeze-thaw weathering. This type of weathering is common in mountain areas where the temperature is around the freezing point of water. Certain frost-susceptible soils expand or heave upon freezing as a result of water migrating via capillary action to grow ice lenses near the freezing front. This same phenomenon occurs within pore spaces of rocks.
The ice accumulations grow larger as they attract liquid water from the surrounding pores. The ice crystal growth weakens the rocks which, in time, break up. It is caused by the approximately 10% expansion of ice when water freezes, which can place considerable stress on anything containing the water as it freezes.When water that has entered the joints freezes, the ice formed strains the walls of the joints and causes the joints to deepen and widen. When the ice thaws, water can flow further into the rock. Repeated freeze-thaw cycles weaken the rocks which, over time, break up along the joints into angular pieces. The splitting of rocks along the joints into blocks is called block disintegration. The blocks of rocks that are detached are of various shapes depending on rock structure.
Physical Weather type Pressure Release
In pressure release, also known as unloading, overlying materials (not necessarily rocks) are removed (by erosion, or other processes), which causes underlying rocks to expand and fracture parallel to the surface. Often the overlying material is heavy, and the underlying rocks experience high pressure under them, for example, a moving glacier. Pressure release may also cause exfoliation to occur.ntrusive igneous rocks (e.g. granite) are formed deep beneath the Earth’s surface. They are under tremendous pressure because of the overlying rock material. When erosion removes the overlying rock material, these intrusive rocks are exposed and the pressure on them is released.
The outer parts of the rocks then tend to expand. The expansion sets up stresses which cause fractures parallel to the rock surface to form. Over time, sheets of rock break away from the exposed rocks along the fractures. Pressure release is also known as “exfoliation” or “sheeting”; these processes result in batholiths and granite domes, an example of which is Dartmoor.
Hydraulic action occurs when water (generally from powerful waves) rushes rapidly into cracks in the rock face, thus trapping a layer of air at the bottom of the crack, compressing it and weakening the rock. When the wave retreats, the trapped air is suddenly released with explosive force.Salt crystallization, otherwise known as haloclasty, causes disintegration of rocks when saline (see salinity) solutions seep into cracks and joints in the rocks and evaporate, leaving salt crystals behind.
These salt crystals expand as they are heated up, exerting pressure on the confining rock.Salt crystallization may also take place when solutions decompose rocks (for example, limestone and chalk) to form salt solutions of sodium sulfate or sodium carbonate, of which the moisture evaporates to form their respective salt crystals.The salts which have proved most effective in disintegrating rocks are sodium sulfate, magnesium sulfate, and calcium chloride. Some of these salts can expand up to three times or even more.It is normally associated with arid climates where strong heating causes strong evaporation and therefore salt crystallization. It is also common along coasts.
An example of salt weathering can be seen in the honeycombed stones in sea wall. Honeycomb is a type of tafoni, a class of cavernous rock weathering structures, which likely develop in large part by chemical and physical salt weathering processes.
native consolidated rock underlying the surface of a terrestrial planet, usually the Earth. Above the bedrock is usually an area of broken and weathered unconsolidated rock in the basal subsoil.
In geology, denudation is the long-term sum of processes that cause the wearing away of the earth’s surface leading to a reduction in elevation and relief of landforms and landscapes. Endogenetic processes such as volcanoes, earthquakes, and plate tectonics uplift and expose continental crust to the exogenetic denudation processes of weathering, erosion, and mass wasting.
Dynamic equilibrium Model
surface-parallel fracture systems in rock often leading to erosion of concentric slabs
Scientific study of landforms and the processes that shape them. Geomorphologists seek to understand why landscapes look the way they do. Geomorphic processes are influenced by tectonics, climate, ecology, and human activity, and equally, many of these drivers can be affected by the ongoing evolution of the Earth’s surface. The form of the Earth’s surface evolves in response to a combination of natural and anthropogenic processes, and responds to the balance between processes that add material and those that remove it. Such processes may act across very many lengthscales and timescales. On the broadest scales, the landscape is built up through tectonic uplift and volcanism.
Denudation occurs by erosion and mass wasting, which 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 (tectonic or sedimentary) and subtractive (erosive) processes.
layer of loose, heterogeneous material covering solid rock. It includes dust, soil, broken rock, and other related materials. Regolith originates from weathering and biological processes; if it contains a significant proportion of biological compounds it is more conventionally referred to as soil.
People also call various types of earthly regolith by such names as dirt, dust, gravel, sand, and (when wet) mud. The presence of regolith is one of the important factors for most life, since few plants can grow on or within solid rock and animals would be unable to burrow or build shelter without loose material.
Sediment is naturally-occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself.
a landscape shaped by the dissolution of a layer or layers of soluble bedrock, usually carbonate rock such as limestone or dolomite.Due to subterranean drainage, there may be very limited surface water, even to the absence of all rivers and lakes. Karst topography is characterized by subterranean limestone caverns, carved by groundwater.Karst landforms are generally the result of mildly acidic water acting on weakly soluble bedrock such as limestone or dolostone.
The mildly acidic water begins to dissolve the surface along fractures or bedding planes in the limestone bedrock. Over time, these fractures enlarge as the bedrock continues to dissolve. Openings in the rock increase in size, and an underground drainage system begins to develop, allowing more water to pass through the area, and accelerating the formation of underground karst features
Process of soil, regolith, and rock move downslope under the force of gravity. Types of mass wasting include creep, slides, flows, topples, and falls, each with its own characteristic features, and taking place over timescales from seconds to years.
When the gravitational force acting on a slope exceeds its resisting force, slope failure (mass wasting) occurs. The slope material’s strength and cohesion and the amount of internal friction between material help maintain the slope’s stability and are known collectively as the slope’s shear strength. The steepest angle that a cohesionless slope can maintain without losing its stability is known as its angle of repose.
When a slope possesses this angle, its shear strength perfectly counterbalances the force of gravity acting upon it.
is loose, unconsolidated (not cemented together into a solid rock), soil or sediments, eroded, deposited, and reshaped by water in some form in a non-marine setting. Alluvium is typically made up of a variety of materials, including fine particles of silt and clay and larger particles of sand and gravel. When this loose alluvial material is deposited or cemented into a lithological unit, or lithified, it would be called an alluvial deposit.
Drainage Density and Patterns
the total length of all the streams and rivers in a drainage basin divided by the total area of the drainage basin. It is a measure of how well or how poorly a watershed is drained by stream channels.
It is equal to the reciprocal of the constant of channel maintenance and equal to the reciprocal of two times the length of overland flow. Drainage density depends upon both climate and physical characteristics of the drainage basin. Soil permeability (infiltration difficulty) and underlying rock type affect the runoff in a watershed; impermeable ground or exposed bedrock will lead to an increase in surface water runoff and therefore to more frequent streams. Rugged regions or those with high relief will also have a higher drainage density than other drainage basins if the other characteristics of the basin are the same.
Pathogens ( Fecal Coliform )
Anaerobic Pathogen. Failing home septic systems can allow coliforms in the effluent to flow into the water table, aquifers, drainage ditches and nearby surface waters.
Sewage connections that are connected to storm drain pipes can also allow human sewage into surface waters. Some older industrial cities, particularly in the Northeast and Midwest of the United States, use a combined sewer system to handle waste. A combined sewer carries both domestic sewage and stormwater.
During high rainfall periods, a combined sewer can become overloaded and overflow to a nearby stream or river, bypassing treatment. Aerobic decomposition of this material can reduce dissolved oxygen levels if discharged into rivers or waterways. This may reduce the oxygen level enough to kill fish and other aquatic life.
Reduction of fecal coliform in wastewater may require the use of chlorine and other disinfectant chemicals. Such materials may kill the fecal coliform and disease bacteria. They also kill bacteria essential to the proper balance of the aquatic environment, endangering the survival of species dependent on those bacteria. So higher levels of fecal coliform require higher levels of chlorine, threatening those aquatic organisms.
A floodplain, or flood plain, is a flat or nearly flat land adjacent to a stream or river that stretches from the banks of its channel to the base of the enclosing valley walls and experiences flooding during periods of high discharge. It includes the floodway, which consists of the stream channel and adjacent areas that carry flood flows, and the flood fringe, which are areas covered by the flood, but which do not experience a strong current.
coverage against property loss from flooding. To determine risk factors for specific properties, insurers will often refer to topographical maps that denote lowlands and floodplains that are susceptible to flooding.
is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and ocean environments and are subject to both marine influences, such as tides, waves, and the influx of saline water; and riverine influences, such as flows of fresh water and sediment. The inflow of both seawater and freshwater provide high levels of nutrients in both the water column and sediment, making estuaries among the most productive natural habitats in the world
A delta is a landform that is formed at the mouth of a river where that river flows into an ocean, sea, estuary, lake, reservoir, flat arid area, or another river. Deltas are formed from the deposition of the sediment carried by the river as the flow leaves the mouth of the river. Over long periods of time, this deposition builds the characteristic geographic pattern of a river delta.
a relatively flat landform created by the deposition of sediment over a long period of time by one or more rivers coming from highland regions, from which alluvial soil forms.
A floodplain is part of the process, being the smaller area over which the rivers flood at a particular period of time, whereas the alluvial plain is the larger area representing the region over which the floodplains have shifted over geological time.
the processes associated with rivers and streams and the deposits and landforms created by them. Fluvial processes comprise the motion of sediment and erosion or deposition on the river bed.Erosion by moving water can happen in two ways. Firstly, the movement of water across the bed exerts a shear stress directly onto the bed. If the cohesive strength of the substrate is lower than the shear exerted, or the bed is composed of loose sediment which can be mobilized by such stresses, then the bed will be lowered purely by clearwater flow. However, if the river carries significant quantities of sediment, this material can act as tools to enhance wear of the bed (abrasion).
At the same time the fragments themselves are ground down, becoming smaller and more rounded (attrition).Sediment in rivers is transported as either bedload (the coarser fragments which move close to the bed) or suspended load (finer fragments carried in the water). There is also a component carried as dissolved material.
A meander is formed when the moving water in a stream erodes the outer banks and widens its valley.
A stream of any volume may assume a meandering course, alternatively eroding sediments from the outside of a bend and depositing them on the inside. The result is a snaking pattern as the stream meanders back and forth across its down-valley axis. When a meander gets cut off from the main stream, an oxbow lake is formed.
Over time meanders migrate downstream, sometimes in such a short time as to create civil engineering problems for local municipalities attempting to maintain stable roads and bridges.
a U-shaped body of water formed when a wide meander from the main stem of a river is cut off to create a lake. This landform is called an oxbow lake for the distinctive curved shape.
An oxbow lake is formed when a river creates a meander, due to the river’s eroding the banks through hydraulic action and abrasion/corrosion. After a long period of time, the meander becomes very curved, and eventually the neck of the meander will touch the opposite side and the river will cut through the neck, cutting off the meander to form the oxbow lake.
a hydrologic term for any tributary stream that runs parallel to, and within the floodplain of, a larger river which the stream eventually joins. Where the two meet is known as a belated confluence or deferred junction.
This is especially the characteristic when such a stream is forced to flow along the base of the main river’s natural levee. The name comes from the Yazoo River, which runs parallel to the Mississippi River for 280 km (175 miles) before converging, constrained from doing so by the river’s levees.
Stream Load (types);
A geologic term referring to the solid matter carried by a stream . Erosion continually removes mineral material from the bed and banks of the stream channel, adding this material to the regular flow of water. The amount of solid load that a stream can carry, or stream capacity, is measured in metric tons per day, passing a given location. Stream capacity is dependent upon the stream’s velocity, the amount of water flow, and the gradation (because streams that occur on steeper slopes tend to have greater flow and velocity).
Stream Load Types
Mineral materials of many different shapes and particle sizes erode and contribute to overall stream load.
Differences in the size of those materials determine how they will be transported down stream. Stream load is broken into three types: dissolved load, suspended load, and bed load
Stream Load;Dissolved Load
Dissolved matter is invisible, and is transported in the form of chemical ions. All streams carry some type of dissolved load. This type of load can result from mineral alteration from chemical erosion, or may even be the result of groundwater seepage into the stream. Materials comprising the dissolved load have the smallest particle size of the three load types
Stream LoadSuspended Load
Suspended load is composed of fine sediment particles suspended and transported through the stream. These materials are too large to be dissolved, but too small to lie on the bed of the stream. Stream flow keeps these suspended materials, such as clay and silt, from settling on the stream bed.
Suspended load is the result of material eroded by hydraulic action at the stream surface bordering the channel as well as erosion of the channel itself. Suspended load accounts for the largest majority of stream load
Stream LoadBed Load
Bed load rolls slowly along the floor of the stream. These include the largest and heaviest materials in the stream, ranging from sand and gravel to cobbles and boulders.
There are two main ways to transport bed load: traction and saltation. Traction describes the “scooting and rolling” of particles along the bed . In stream load transport, saltation is a bounce-like movement, occurring when large particles are suspended in the stream for a short distance after which they fall to the bed, dislodging particles from the bed. The dislodged particles move downstream a short distance where they fall to the bed, again loosening bed load particles upon impact.
A flood is an overflow of an expanse of water that submerges land. The EU Floods directive defines a flood as a temporary covering by water of land not normally covered by water. In the sense of “flowing water”, the word may also be applied to the inflow of the tide. Flooding may result from the volume of water within a body of water, such as a river or lake, which overflows or breaks levees, with the result that some of the water escapes its usual boundaries
Biological Oxygen Demand
a chemical procedure for determining the amount of dissolved oxygen needed by aerobic biological organisms in a body of water to break down organic material present in a given water sample at certain temperature over a specific time period. It is not a precise quantitative test, although it is widely used as an indication of the organic quality of water.
Oxygen saturation in the environment generally refers to the amount of oxygen dissolved in the soil or bodies of water. Environmental oxygenation can be important to the sustainability of a particular ecosystem. Insufficient oxygen (environmental hypoxia) may occur in bodies of water such as ponds and rivers, tending to suppress the presence of aerobic organisms such as fish. Deoxygenation increases the relative population of anaerobic organisms such as plants and some bacteria, resulting in fish kills and other adverse events. The net effect is to alter the balance of nature by increasing the concentration of anaerobic over aerobic species.
activity of the winds and more specifically, to the winds’ ability to shape the surface. Winds may erode, transport, and deposit materials, and are effective agents in regions with sparse vegetation and a large supply of unconsolidated sediments.
Although water is a much more powerful eroding force than wind, aeolian processes are important in arid environments such as deserts. Wind erodes the Earth’s surface by deflation (the removal of loose, fine-grained particles), by the turbulent eddy action of the wind and by abrasion (the wearing down of surfaces by the grinding action and sandblasting of windborne particles)
a desert surface that is covered with closely packed, interlocking angular or rounded rock fragments of pebble and cobble size. They form by the gradual removal of the sand, dust and other fine grained material by the wind and intermittent rain leaving only the larger fragments behind.
a large, relatively flat area of desert covered with wind-swept sand with little or no vegetative cover.
Erg is defined as a desert area that contains more than 125 square kilometers of aeolian or wind-blown sand and where sand covers more than 20% of the surface.Sand seas and dune fields generally occur in regions downwind of copious sources of dry, loose sand, such as dry riverbeds and deltas, floodplains, glacial outwash plains, dry lakes, and beaches. Almost all major ergs are located downwind from river beds in areas that are too dry to support extensive vegetative cover and are thus subject to long-continued wind erosion.
Radially symmetrical, star dunes are pyramidal sand mounds with slipfaces on three or more arms that radiate from the high center of the mound. They tend to accumulate in areas with multidirectional wind regimes.
Star dunes grow upward rather than laterally. They dominate the Grand Erg Oriental of the Sahara. In other deserts, they occur around the margins of the sand seas, particularly near topographic barriers. In the southeast Badain Jaran Desert of China, the star dunes are up to 500 metres tall and may be the tallest dunes on Earth.
Eolian sediment formed by the accumulation of wind-blown silt, typically in the 20–50 micron size range, and lesser and variable amounts of sand and clay that are loosely cemented by calcium carbonate. It is usually homogeneous and highly porous and is traversed by vertical capillaries that permit the sediment to fracture and form vertical bluffs. Loess tends to develop into highly rich soils.
Under appropriate climatic conditions it is some of the most agriculturally productive terrain in the world.
A playa lake is formed when rain fills a round depression in the landscape, creating a small lake. The water is generally freshwater, When all of the water evaporates, a playa is formed. The playa appears as a flat bed of clay, generally encrusted with precipitated salts.
These evaporate minerals are a concentration of weathering products that have been left behind. Some examples of evaporite minerals are sodium carbonate, borax, and other salts. Playas are often found in bajadas, a depositional landform of desert environments
is an arc-shaped sand ridge, comprising well-sorted sand. This type of dune possesses two “horns” that face downwind, with the slip face (the downwind slope) at the angle of repose of sand, or approximately 35 degrees
rocks that have been abraded, pitted, etched, grooved, or polished by wind-driven sand or ice crystals. These geomorphic features are most typically found in arid environments where there is little vegetation to interfere with aeolian particle transport, where there are frequently strong winds, and where there is a steady but not overwhelming supply of sand.
The slow movement of soil and rock debris by gravity which is usually not perceptible except through extended observation.
However, the term can also describe the rolling of dislodged soil particles 0.5 to 1.0 mm in diameter by wind along the soil surface.
a specific type of particle transport by fluids such as wind, or the denser fluid water. It occurs when loose material is removed from a bed and carried by the fluid, before being transported back to the surface. Examples include pebble transport by rivers, sand drift over desert surfaces, soil blowing over fields.
At low fluid velocities, loose material rolls downstream, staying in contact with the surface. This is called creep or reptation. Here the forces exerted by the fluid on the particle are only enough to roll the particle around the point of contact with the surface
Butte – a conspicuous isolated hill with steep, often vertical sides and a small, relatively flat top. It is smaller than mesas, plateaus, and tables. In differentiating mesas and buttes, geographers use the rule that a mesa has a top wider than its height, while a butte’s top is narrower.
Tided Dunes/ Free Dunes
Dunes form where constructive waves encourage the accumulation of sand, and where prevailing onshore winds blow this sand inland. There need to be obstacles e.g. vegetation, pebbles etc. to trap the moving sand grains. As the sand grains get trapped they start to accumulate, starting dune formation. The wind then starts to affect the mound of sand by eroding sand particles from the windward side and depositing them on the leeward side. Gradually this action causes the dune to “migrate” inland, as it does so it accumulates more and more sand.
Dunes provide privacy and shelter from the wind.
A stream found in an area that is too dry to have spawned such a flow. The flow originates in some moister section
an isolated rock hill, knob, ridge, or small mountain that rises abruptly from a gently sloping or virtually level surrounding plain.
Volcanic or other processes may give rise to a body of rock resistant to erosion, inside a body of softer rock such as limestone which is more susceptible to erosion. When the less resistant rock is eroded away to form a plain, the more resistant rock is left behind as an isolated mountain. The strength of the uneroded rock is often attributed to the tightness of its jointing.
the removal of loose rock material, sand, and dust by the wind
a type of dry terrain where softer sedimentary rocks and clay-rich soils have been extensively eroded by wind and water. It can resemble malpais, a terrain of volcanic rock. Canyons, ravines, gullies, hoodoos and other such geological forms are common in badlands.
Basins and Range
a type of topography characterized by a series of separate and parallel mountain ranges with broad valleys interposed, extending over a more or less wide area. Basin and range topography results from crustal extension.
As the crust stretches, faults develop to accommodate the extension. In the western United States, this topography is built by a number of normal faults that meet at a basal detachment fault. The basins are down-fallen blocks of crust and the ranges are relatively uplifted blocks, many of which tilt slightly in one direction at their tops due to the motion of their bottoms along the main detachment fault.
Blowouts are sandy depressions in a sand dune ecosystem caused by the removal of sediments by wind. Blowouts occur in partially vegetated dunefields or sandhills. A blowout forms when a patch of protective vegetation is lost, allowing strong winds to “blow out” sand and form a depression.
An alluvial fan is a fan-shaped deposit formed where a fast flowing stream flattens, slows, and spreads typically at the exit of a canyon onto a flatter plain.
A convergence of neighboring alluvial fans into a single apron of deposits against a slope is called a bajada, or compound alluvial fanAlluvial fans are often found in desert areas subject to periodic flash floods from nearby thunderstorms in local hills. They are common around the margins of the sedimentary basins of the Basin and Range province of southwestern North America. The typical watercourse in an arid climate has a large, funnel-shaped basin at the top, leading to a narrow defile, which opens out into an alluvial fan at the bottom. Multiple braided streams are usually present and active during water flows.
a dry river, creek or stream bed—gulch that temporarily or seasonally fills and flows after sufficient rain.
one of a number of channel types and has a channel that consists of a network of small channels separated by small and often temporary islands called braid bars.
Once a given system crosses a threshold value for sediment load it will convert from a meandering system to a braided system.
material is added to a landform or land mass. Fluids such as wind and water, as well as sediment flowing via gravity, transport previously eroded sediment, which, at the loss of enough kinetic energy in the fluid, is deposited, building up layers of sediment.
an extent or area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean. In closed drainage basins the water converges to a single point inside the basin, known as a sink, which may be a permanent lake, dry lake, or a point where surface water is lost underground