A

Abiotic – lit. not from living things. In physical geography, used to describe non-living components of an environment such as rock or water.

Ablation – the net loss of water from a glacier through melting, calving, evaporation, sublimation or wind transport. Is dominant to accumulation over space and time when the glacier enters warmer conditions.

Abrasion – degradation of the land through the scouring action of materials being carried by an agent of erosion . Rates vary according to amount of material carried, energy of the agent and hardness of materials involved.

Absolute humidity - the amount of water vapour in the air in grams per cubic metre.

Absorption - the absorbing of insolation to solids, liquids and gases on the surface and in the atmosphere.

Abyssal plain - large, relatively flat areas of ocean floor found at 5,000-6,000m below sea level. If sediments are discharged from a river and deposit relatively quickly onto the plain they may form an abyssal fan.

Accessibility - the level of difficulty associated with getting to a location or feature within a larger area measured in distance, time and/or cost.

Accretion - growth of a natural feature by enlargement due to the addition of more of the same material.

Accumulation - the net gain in ice mass by precipitation of snow, arrival of snow from avalanche, arrival of snow by wind transport or refreezing of melt water. Is dominant to ablation over space and time when the glacier enters colder conditions.

Acidification - the increase in acidity in an environment due to the development of a particular biome or due to human pollution causing unnaturally high levels of acid rain.

Acid lava - lavas containing high percentage of silica. Tend to have high melting points and to be highly viscous.

Acidophilous - an organism which prefers acid conditions.

Acid rain - refers to the unnatural increase, through human pollution, in the acidity of water precipitation. Most commonly sulphuric and nitric acids formed from by-products of fossil-fuel burning and metal smelting.

Acquired immune deficiency syndrome - a fatal syndrome caused by HIV. Main characteristic is a greatly reduced ability of the body to fight infection. Victims usually die from other illnesses they can no longer fight, rather than aids itself, which can lead to underreporting.

Acrotelm - the upper layer of peat deposits

Active layer - the upper few metres of soil in a periglacial area which undergoes thawing in summer and is prone to mass movement relative to the permafrost layer below.

Adiabatic - change in temperature due to expansion or contraction of a parcel of air which thus change the pressure and therefore the temperature. No heat transfer between the air parcel and the surrounding air.

Adret slope - a south-facing slope.

Adsorption - physical or chemical bonding of solid particles with liquids or gases.

Advection - horizontal transfer of heat by a horizontally moving air mass.

Aeolian - lit. 'of the wind' Refers to transportation, erosion and deposition by wind action.

Afforestation - planting of trees on previously un-wooded land.

Aftershock - ground tremors occurring after a major earthquake but associated with the same focus point.

Agent of erosion - the direct source of movement that can cause erosion through the transfer of energy or transport of rock material: water (rivers and waves), wind and ice.

Agglomeration - the grouping together of businesses in the same area to minimize costs through linkages.

Aggradation - deposition of load within river channels.

Agribusiness - corporations organized to provide vertical linkages both below and above the farm itself.

Agriculture - the science, art, and business of cultivating the soil, producing crops, and raising livestock; farming.

Agricultural chain - every step in the process(es) that lead to the consumption of food.

Agricultural revolution - a period of fundamental changes to agricultural systems which tend to concentrate land and production into fewer hands while increasing yields. Changes may be organizational and technological.

Aid - transfer of resources from a donor to a recipient. May be undertaken at a variety of scales usually under the following conditions:         

bilaterally between national governments. The donor will usually attach specific conditions both economic and political.         

multilaterally where donors contribute to an agency (e.g. World Bank) which then distributes to recipients again imposing political and economic conditions but at a system level.         

voluntary aid - charitable, non-governmental organizations (NGOs) generate income from collection campaigns in the donor country for use in smaller-scale often community level schemes in recipient countries. Usually not tied.

Aids - see acquired immune deficiency syndrome

Air mass - large body of air with shared temperature and humidity characteristics associated with its area of origin e.g. maritime or continental; tropical or polar.

Air pressure - the force of the atmosphere on the surface.

Albedo - the amount of insolation reflected from the atmosphere and surface back to space. Darker, heavily vegetated surfaces have low albedo, snow and ice have high albedo. Angle of sun causes variation over time of albedo of water surfaces.

Algae - collective name for a group of chlorophyll-containing plants, ranging in size from single cells to stems, including seaweeds and freshwater forms.

Algal bloom - rapid growth of phytoplankton in water bodies usually in the surface layers. May be hazardous both through the production of toxins and through the blocking of insolation to lower layers.

Allochthonous sediment - one in which the major components have formed in situ.

Allogenic - when an external environmental factor causes a process to occur.

Alluvial cone - an alluvial fan with highly steep slopes usually found where mountain streams exit narrow valleys.

Alluvial fan - a fan-shaped deposit of river load where energy has been lost due to the river exiting abruptly from a narrow upland valley to a lowland plain.

Alluviation - the process of depositing alluvium.

Alluvium - river deposits found either on the floodplain or historic point-bars.

Alpha index - a measure of connectivity in a network. Expresses the cyclomatic number as a percentage of the maximum possible circuits. A low percentage indicates low connectivity.

Formula is: α = (e-v+1) x 100                                                                                                         2v-5 where e is number of edges and v is number of vertices.

Alternative technology -(usually interchangeable with appropriate or intermediate technology) the use of low-cost, often labour-intensive, technology, based on local resources, that is appropriate to Economically Less Developed Countries. May originate internally or externally.

Altitude - height above sea-level.

Anabatic - the movement of air up slopes due to convection.

Anaerobic - lit. without free oxygen. In geography, applied to waterlogged soils which will then experience reduction of ferric compounds to ferrous compounds and turn from red to blue colourings.

Anastomising - see braiding.

Antecedent drainage - the maintenance of course by an old river over more recent uplifting of the land surface.

Anticyclone - a stable, generally subsiding air mass producing high pressure, warming conditions. The resultant fall in relative humidity leads to clear skies.

Anvil clouds - rapidly rising column of air in a convectional thunderstorm will soon reach the tropopause and be forced to spread in its upper portion to form an anvil shape.

Appropriate technology - see alternative technology. Appropriate technology might more commonly be the term applied to alternative technology originating externally.

Aquaculture - highly managed use of water environments to enhance food production e.g. fish farms.

Aquatic fauna  - all animal species which require the continual presence of water for survival and reproduction.

Aquatic plants - fall into four categories. Emergents ( rooted in sediment and protrude above the surface), free-floaters, floating-leaved (rooted in sediment with leaves floating on the surface), and submergents.

Aquifer - a permeable rock which stores and transfers water. Useful when underlain by impermeable rock to trap the water and allow it to be tapped.

Arable - cultivation of crops such as cereals, legumes, roots and leaves.

Arch - when a cave in the side of a headland is eroded right through to the other side forming a bridge-shaped landform.

Arctic air - an air mass originating over the Arctic Circle.

Area of Outstanding Natural Beauty (AONB) - in the UK, land areas given special protection by act of parliament to preserve their natural beauty. Local authorities maintain strict control over permission for development within them. England has 35, Wales has 4, 1 is astride the border, and N. Ireland has 9.

Arete - a sharp, steed-sided ridge in an upland area. Resultant of enlargement of adjacent corries.

Arid - climatic areas characterized by extreme dryness. Simple definitions set maximum annual precipitation (up to 250mm per year). More complex definitions recognize the importance of evapotranspiration (or potential evapotranspiration ) where precipitation is very low).

Arroyo - approximate rectangular shaped valley cut in floodplain alluvium, with a smaller stream in the base. Usually found in semi-arid areas.

Artesian - the upward movement of groundwater by hydrostatic pressure.

Artificial flood - deliberate release of water from dam reservoirs to create downstream flooding that is beneficial to farmland or wetland areas.

Asian Tigers - hong Kong, Singapore, South Korea and Taiwan. So named for their rapid economic growth from 1970s to crash of 1997.

Aspect -direction in which a slope faces.

Asthenosphere - layer of rock in the mantle approximately 80km deep and at a temperature of 1400°C. Rocks here become much softer and more easily deformed than in the lithosphere above.

Athalassohaline - water with a different proportion of dissolved salts than is usual in seawater.

Atmosphere - layer of gases surrounding earth and held there by gravity. Nitrogen forms 78.09% by volume and Oxygen 20.95%. The remaining 0.96% is made up of a further 19 gases. The boundary of the atmosphere is 1000km above sea level but 99% of the gases are held in the lower 40km. This is split into three layers - the troposphere and the stratosphere separated by the tropopause. Carbon dioxide in the troposphere allows photosynthesis and also holds long-wave radiation to give warmth. Temperatures fall with altitude at a rate of approximately 6.5°C per km to the tropopause where they are stable. Ozone in the stratosphere traps ultraviolet radiation and leads to an increase in temperature in this layer.

Atmospheric particulates - solids present in the atmosphere. May be naturally occurring dusts and soils etc. or human pollutants such as smoke.

Atoll - a ring-shaped coral reef.

Attrition - a process of erosion where the collisions between parts of the load lead to comminution.

Autonomy - the right of self-government. Exists at nation-state and sub-national, regional levels.

Autotroph - an organism that can produce nutritional organic substances from simple inorganic substances. Thus, plants grow by synthesizing carbon dioxide and water using sunlight.

Avalanche - rapid, down slope mass movement of ice and/or snow due to a trigger overcoming reduced friction in an unstable accumulation.

Azonal soil - a soil which does not demonstrate much, if any, evidence of soil-forming processes. Often little more than regolith, they are controlled by parent material and relief.

B

Backshore – the beach above the high water, or high tide, mark which is usually untouched by wave action.

Back-wall – the steep cliff face at the rear of a corrie.

Backward integration – vertical integration in an upstream direction i.e. a company merging with or buying out a supplier.

Backwash -used in both physical and human geography

in physical geography, the movement of water down a beach to the sea after having run up the beach in the swash.

in human geography, the movement of resources from periphery to core through a series of circuits: capital concentrates in the core, depriving the periphery and reducing wealth generation there; migration tends to take younger, more employable workers to the core leaving older, less productive workers in the periphery; lack of investment in services, amenities and infrastructure further widen the gap.

Backwater -area of still water created by an impediment to drainage e.g. a sediment bar across an ox-bow lake.

Bacteria -a class of organisms known as Prokaryotes in which the cell has no nucleus. They are single-cell microbes which can be found virtually everywhere. They 'eat' almost anything which lends them an enormous variety of very useful functions, although they can also be responsible for sickness. Geographers may be interested in the role they play in health patterns, especially in the ELDW, or in soil formation, or many other topic areas.

Bahada -gently sloping plain formed when a number of alluvial fans exiting closely spaced wadis in desert areas coalesce into a larger feature.

Balance of payments -net sum of a country income from and expenditure on foreign trade which can run to a surplus or a deficit.

Balance of trade -the net sum of imports and exports of visible goods. Forms part of the balance of payments along with the same calculation for invisibles.

Bankfull discharge -the maximum discharge that a particular river channel is capable of carrying without flooding.

Baobab tree -a pyrophitic tree found in savannah areas. It has an enormous trunk which stores water and tiny leaves to minimize evapotranspiration.

Bar -see sand bar.

Barchan -crescent-shaped sand dune which form in desert areas experiencing generally constant winds. The 'horns' of the crescent point downwind, having moved ahead more rapidly, where they become sheltered and stable. Sand moves up the windward side and collapses down the leeward side which is steeper. This net movement of sand from the windward to the leeward side causes the dune to move forwards.

Bar chart -bars of equal width placed within perpendicular axes and used to represent varied amounts or frequencies through variations in length.

Barrage -a dam or barrier with adjustable gates and sluices built across an estuary in order to harness tidal energy.

Barrier beach -low-lying, bar-shaped sand and/or coral island lying parallel to but slightly away from a coastline. The landward side tends to be marshy or a lagoon.

Basal sapping -the undercutting and retreat of a slope caused when erosion and/or weathering are concentrated at its base.

Basal slipping -during summer time in warmer glacial areas, limited melting lubricates the base of the glacier allowing it to move more freely. Movement increases pressure, raising temperature and allows further melting as the ice reaches its pressure melting point.

Basalt -an igneous rock, fine-grained and glass-like, formed by rapidly cooled lava often under water.

Base flow -that portion of river discharge derived from groundwater flow.

Base level -the lowest elevation to which erosion can take place. Usually sea-level but could be lower if a river drains into an inland sea or lake whose level is below sea-level.

Basic volcano -where low viscosity, extremely hot lava flows from a vent it will spread rapidly to form a shallow sloped, low altitude cone.

Batholith -a massive intrusive volcanic feature. Magma forces its way into the crust but becomes trapped and solidifies into rock e.g. granite.

Battery farming -intensive, commercial livestock (usually poultry or cattle) production where animals are reared in cages and fed and watered automatically to reduce the per unit cost. May also include hormone treatment.

Bay -a curved indent to the coastline, usually created by greater erosion rates than neighbouring parts of the coast. Bays often contain beaches and provide an area of shelter both for boats and for settlements.

Beach -accumulation of sand and shingle material at a coast or at the fringes of a body of water due either to low energy brought about by sheltered conditions or due to an excess of sediment.

Beach depletion -net loss of sand and/or shingle from a beach due to reduced replenishment while removal processes such as longshore drift continue unabated. Natural replenishment rates are thought to have slowed as sea-levels have risen, river loads have reduced, beaches have stabilized and humans have dredged offshore sediments.

Beach nourishment -human replenishment of depleted beaches using material from land pits or dredged deposits. Beach material may be allowed to move by longshore drift before being returned to where it started.

Beaufort scale -a scale for wind speed, and therefore strength, based on observable effects.

Bedding plane -the boundary between adjacent layers or strata in a sedimentary rock.

Bedload -larger load which is unable to move in suspension but is transported by saltation and traction.

Bedrock -solid rock underlying other surface materials.

Benioff Zone -boundary between an oceanic plate undergoing subduction beneath a continental plate. Characterized by earthquakes and the melting of the oceanic plate.

Benthos - marine organisms which dwell on the seabed.

Bergeron-Findeison process -a theory of raindrop formation. At temperatures between -5 蚓 and -25 蚓 both water droplets and ice crystals exist in the same space. Vapour is sublimated onto the ice crystals and the deficit in vapour is compensated by the evaporation of the water droplets leading to further sublimation and thus growth of the ice crystals. These may coalesce into snowflakes which then overcome gravity and fall. When air temperatures at the surface are greater than zero the flakes melt into water drops before they land.

Bergschrund -a large crevasse at the upper portion of a corrie glacier, close to the back-wall.

Berm -a low ridge towards the rear of a beach marking the uppermost level that waves reached during the previous high tide.

Best-fit line -a line drawn on a scatter-graph, as close to all the points as possible, which thus indicates any trend in the pattern. Points that are very disparate may not provide an opportunity to draw a best-fit line and thus show no trend or correlation. If the points all lie on the line, the correlation is perfect.

Beta index -a measurement of connectivity using the formula

                                    β =   e      

                                           v

where e is number of edges and v is number of vertices. The higher the value of β the greater the connectivity.

Bias -distortion in sampling which means that the sampled data does not represent the population which it is meant to represent.

Bid-rent theory -the idea that land is acquired by the highest bidder which is in turn a function of the user who can make the most profit from the site. Usually related to accessibility.

Bifurcation ratio -in a drainage basin, the relationship between the streams of one order of magnitude and those of the next highest order, obtained by dividing the number of lower order streams with the number of the higher order. The lower the number the greater the risk of flooding. (see also stream order)

Bilharziasis -disease caused by a parasitic worm which enters the human body by penetrating the skin while swimming/bathing/working in infected waters. Mostly found in tropical areas of Africa, Asia and South America. Causes particular problems for the liver and kidneys by mass production of eggs. Leads to anemia and lethargy but not usually directly fatal. At least 200 million infected and a further billion under threat.

Biodiversity -the range of species in a particular area.

Biofuel -fuel derived from biomass. In primitive form this could mean burning firewood. More usually used to refer to gas or alcohol products derived from biomass for burning either to produce electricity or as vehicle fuels.

Biogas -a form of biofuel where methane gas is obtained from decomposing biomass for energy use.

Biological control -use of natural organisms to fight weeds and pests in agriculture.

Biological Oxygen Demand - See BOD

Biomass -total amount of organic material.

Biome -large-scale natural community named for its dominant vegetation.

Biomonitoring -surveillance of an ecosystem to monitor and record change.

Biosphere -a reference to the totality of the earth surface and atmosphere that is inhabited by living organisms.

Biosphere Reserve -a designation given and coordinated by UNESCO to conserve natural systems through education and research.

Biota - plant and animal life.

Biotope - non-living part of an ecosystem with the idea of the space in which the biota exist.

Biotechnology -use of biological knowledge and research to developing technologies especially in pharmaceutical areas.

Biotic factors -the influence of living organisms on the growth and distribution of plants such as shade provided by leaves or seed dispersal by animals.

Bi-polar test -the provision of two opposite views between which strength of feeling can be measured e.g. a scale of one to five in which one represents negative feelings and five positive.

Birth control programme -a systematic approach to controlling the birth rate in a particular area, usually at the national or sub-national level in an ELDC.

Birth rate -number of live births per thousand people per year.

Bivalve - any animal with a two-part, hinged shell.

Blizzard -a heavy snowstorm combined with high speed wind.

Blockfield -extensive area of large angular rock fragments in periglacial regions. 

Blocking anticyclone -when an anticyclone breaks northwards to 50°-70°N where it can come to rest for several weeks and divert other, more usual weather systems, off their usual paths leading to extended periods of clear, dry weather.

Blowout depression -a small, shallow bowl-shaped feature created by wind erosion in coastal and arid areas.

Bluff -slope created by lateral river erosion causing the retreat of interlocking spurs . 

B.O.D. - biological oxygen demand - mg per litre of dissolved oxygen used by micro-organisms during the feeding process on the organic content of a body of water. It is thus possible to determine the level of organic pollution of the water. A BOD of <3mg/l can be considered to indicate 'clean' water while one in excess of 30mg/l would indicate gross pollution.

Bog -waterlogged, spongy ground forming in cooler, high-rainfall areas. Only smaller plants are able to grow and their decomposition is very slow leading to peat soil formation. Often found in upland areas.

Boreal -most usually used to mean northern in reference to latitudes 45°-75°N and in association with the largely coniferous forests found here.

Boserup, Ester -a Danish economist who suggested that the ideas of Malthus regarding the relationship between population and resources, particularly food, did not hold because technological development allowed resource production to support larger populations than previously thought possible, or 'necessity is the mother of invention' More recent studies suggest the reverse may be true.

Bottom fauna -see benthos.

Bottomset beds -layers of sediment in a delta found furthest from the river mouth and formed from flocculated clay particles.

Bottom-up -ideas, initiatives or developments originating in and flowing from the lower levels of a hierarchy further up the hierarchy.

Boulder -a size-classification of rock pieces. Boulders should be lumps of rock at least 200 mm in diameter.

Boulder clay -see till.

Bourne -a seasonal river which flows in normally dry valleys during wetter periods of the year.

B.P. - before present -an alternative, more accurate, means of identifying past years.

Brackish -a slightly saline environment where sea water inputs are moderated by an inflow of freshwater.

Braiding -when a river is forced to divide into multiple channels which interlink with each other. A feature of rivers with high loads and occupying wide, flat areas of low relief.

Brandt Report -produced in 1980 by a commission headed by Willy Brandt, former West German Chancellor. Its focus was the difference in social, economic and political well-being between the EMDW and ELDW, then referred to as the North and the South respectively. It concluded that both sets of countries were interdependent on each other, and neither should raise barriers against the other.

Breaker -an overextended wave which then collapses sending water forward. Occurs when sea waves enter shallow water and are slowed at their base by friction.

Breaking point -in gravity models, the point at which customers prefer to travel to one centre rather than another.

Break of bulk -a site where cargo is broken down from a large, bulk carrying unit, to smaller scale units, usually involving a change in the mode of transport.

Breakpoint bar -a sand bar parallel to the coast which is located approximately at the point where waves begin to break.

Breccia -a sedimentary rock made up of large, angular grains which have been cemented together.

Bridging point -a site factor. Early settlements were often built where a river was shallow enough to be forded. As bridge building improved, more points on rivers were suitable for building crossings.

Brook -a small stream.

Bronze Age settlement -settlements, or evidence of settlement, dating between 3900BP to 2500BP.

Brown earth -type of soil associated with northern Europe in deciduous woodland areas. High leaf litter in autumn provides plenty of material for decomposition into a rich humus which is mixed into the soil by soil fauna creating the rich brown colour.

Brownfield site -a site, either derelict or holding very old buildings, which could be redeveloped for new uses.

Burgess, Earnest -an American sociologist who proposed the concentric-ring model of urban land use. Based on Chicago, the model was developed by applying ecological rules and relationships to the behaviour of people in creating their urban areas.

Business cycle -regular pattern of 'boom and bust'upturns and downturns in economic demand and output repeating every 5-7 years.

Business park -purpose-built or redeveloped areas for companies requiring office space rather than industrial space. Some high-tech production may also appear. Characterized by low-rise, highly modern units, well-spaced and landscaped. May also include leisure and convenience amenities for employees.

Bustee -the name for a shanty town in India.

Buys Ballot -a Dutch scientist. Proposed in 1857 that, if you stand with the wind to your back in the Northern hemisphere, low pressure lies to your left. Vice versa in the Southern hemisphere.

C

Calcareous soils– soils controlled by a calcium-based parent-material such as limestone or chalk.

Calcification – deposition of calcium carbonate in a soil in low precipitation areas having high rates of evaporation and thus water deficit.

Calcium carbonate – a compound with the formula CaCO3.

Caldera – a volcanic cone where the original top and centre have been removed either through a massive eruption or through collapse leaving the base of the cone as a large ring-shaped ridge.

Caliche - an alkaline salt deposit (crust) created by salinisation.

Calorie intake -a measure of the amount of energy derived from food. Requirements vary with sex, age, size and environmental factors. One of the measures having a bearing on health.

Calving -a form of ablation whereby a mass of ice breaks away from a glacier or sheet. After reaching a body of water the tip of the glacial mass is floated creating stresses with the main body remaining on land that cause it to snap free and float away as an iceberg.

Cambrian -in geologic time, a period lasting from 570m to 505m years ago.

Canopy -when the trees in a woodland or forest area are close enough together that the upper leaf layer of the trees form a more or less consistent cover.

Canyon -a large-scale, steep-sided valley which is deeper than it is wide.

CAP -see common agricultural policy.

Capillary action -the upward movement of water through a channels in a substance. In geography, most commonly the upward movement of water through a soil. Caused by adhesion of the water to the channel surface and cohesion of water molecules to one another.

Capillary water -the water that moves around the soil and is available for plant use.

Capital -three forms can be identified:

money capital is the finance to start or expand a business that comes either from shareholders or from loans.

fixed capital is the investment of existing buildings or equipment to a business

social capital is the social amenity infrastructure of an area that may attract a business to set up there.

Capitalism -a social and economic system relying on market mechanisms to allocate factors of production which are privately rather than state owned.

Carbonation -a form of chemical weathering where natural rainwater, a weak carbonic acid, reacts with calcium carbonate in rock to produce calcium bicarbonate.

Carbon dating -a means of dating organic material based on the fact that carbon-14, a radioactive component of all living things, decays at a known rate over time from death.

Carbon dioxide (CO2) -an atmospheric gas which has in modern times made up approximately 0.03% of the atmosphere by volume. It is vital for photosynthesis and for its contribution to the Greenhouse Effect which allows life to exist on earth by absorbing long-wave radiation from the earth surface and holding the energy in what we know as air temperature.

Carboniferous limestone -a sedimentary rock laid down in the geological period 280-345 million years BP (the Carboniferous period). Has a calcium carbonate content of at least 80% meaning it was laid down in highly productive, warm, shallow seas which provided the necessary skeletal remains. Characterized by thick, well-jointed beds which are pervious and allow rapid carbonation leading to karst scenery.

Carbon monoxide (CO) -a gas produced through inefficient and therefore incomplete combustion of fossil fuels.

Carbon tax -taxes levied on fossil fuel products as a disincentive to consume them as a strategy to slow global warming.

Cardinal points -North, South, East, West.

Carnivore -an animal that consumes other animals for food.

Carr -an area of swamp whose dominant flora is a mixture of trees, bushes and shrubs.

Carrying capacity -the idea that any given environment can only support a finite population. Originating in ecology for plant communities, social geographers have tried to apply the idea to human populations.

Cartel -a group of producers within a single industry who agree to limit supply to keep prices high. To be effective they must control most of the productive capacity of the industry and every member must abide by the agreement. Not appropriate to all industries. Most countries legislate against cartels as they exploit the consumer to too great a degree. One famous, and legal, cartel is OPEC.

Cartography -map and chart making.

Cash cropping -the growing of crops for sale as opposed to consumption.

Catastrophism -the belief that landscape is the result of sudden, catastrophic events, rather than slow, day-to-day processes. Outmoded, but recognized as a contributory factor.

Catchment area -the area of land from which precipitation makes its way to a particular river channel.

Catena -sequence of soils on a slope where the differences between them are a direct function of the change in slope.

Cation exchange capacity -ability of the soil to retain cations and thus be fertile.

Catotelm -the lower level or layer of a peat deposit.

Cave -a recess in the ground.

Cavern -a large cave.

Cavitation -creation of pot holes in a stream bed due to the blasting effect of particles thrown against it by the formation and collapse of air bubbles. The bubbles form in streams flowing at high speed or under high pressure.

CBD -see central business district

Census -the collection of data about a population. At its simplest, a count of the number of people in an area. EMDC governments collect much more data to do with demographics, housing, social patterns and economic factors. These are usually carried out every ten years and participation is compulsory.

Central business district -a centrally-located (in space and/or time) zone of an urban area, containing the principal commercial, professional, retail and governmental functions.

Centrally planned economy -see command economy.

Central place theory -the idea that all settlements influence the area surrounding them in the provision of goods and services -the sphere of influence. This leads to a regular spacing of settlements of a similar size and function across a landscape. Larger settlements-spheres of influence overlay those of smaller ones.

CFC -see chloroflurocarbon

Chalk -a porous, sedimentary rock formed mostly from the skeletal remains of marine organisms. Bedding planes and joints increase the permeability. It is relatively soft but, when uplifted, can maintain an upland landscape as the permeability allows the rapid removal of water which slows weathering and erosional degradation.

Channel efficiency -the ability of the channel to conserve energy that may otherwise be lost to friction. Measured by hydraulic radius.

Channel flow -run off of surface water in a defined channel as in a river or stream.

Channelization -straightening and/or deepening of river channels to improve/maintain navigability and for flood control.

Channel morphology -shape and dimensions of the cross-section of a channel.

Chaparral -a biome of scrub vegetation i.e. one dominated by short, woody dense bushes, found in California. Related to maquis of the Mediterranean. Adapted for hot, dry summers and mild winters which may include periods of drought.

Chelation -a form of chemical weathering. Organic acids released during decomposition release iron and aluminium from the A horizon and combine with them to form chelates.

Chemical Oxygen Demand (COD) -a measurement of the organic content of waste material related to the amount of oxygen required for it to be stabilized.

Chemical weathering -a weathering process in which the resultant material is chemically different to the original rock. Usually carried out by dilute acids. Rates will therefore increase with the increased presence of water and increased temperature except for carbonation in which weathering rates increase at lower temperature. Other types include hydration, hydrolysis and oxidation.

Chernozem -soil type often found in continental interiors with a temperate grassland  biome type. Thick grass provides for rich black humus which is extended into the A horizon by fauna during warm summers. Wet spring and early summer leads to leaching. Hot late summer causes capillary action. Up and down movement of water leads to formation of calcium carbonate nodules at about 1m depth.

Chinook -the N. American name for a warm dry wind sinking on the leeward side of a mountain range. See F 鐬 n .

Chi-squared test -the comparison of an actual distribution of points with a random distribution of the same number of points to establish whether or not there is a significant enough difference to say that the actual distribution has occurred for a particular reason.

Χ2=Σ(O-E) 2

                                                                                                                 E

            where O is the observed frequency and E is the expected frequency.

Chloroflurocarbons -chemicals which were used in foam, refrigeration units, and aerosols for many years. Their release into the atmosphere was held responsible for the depletion of helpful ozone in the stratosphere and they also act as a greenhouse gas. Many countries have now banned their use.

Choropleth map -a map using different densities of shading to indicate the distribution of different classes of data by administrative unit across an area.

Chott -the name given to depressions found along and within the northern border zone of the Sahara which fill with water from the overland flow during flash floods. The water may remain for several weeks afterwards allowing a flourishing of vegetation although fauna is limited.

Christaller, Walter -one of the main architects of central place theory.

Cirque -see corrie

CITES - Convention on International Trade in Endangered Species of Wild Flora and Fauna -an international agreement designed to limit the harmful impacts of removal of plants and animals from their natural habitats, especially those whose population numbers decline to critical levels. www.cites.org

City Action team -group of civil servants charged by 1980s and 1990s UK government with formulating solutions to inner city decay, particularly problems of unemployment and derelict land.

Clapotis -phenomenon where pattern of incoming sea waves exactly matches waves reflected by a sea wall or a sea cliff resulting in a static pattern of crests and troughs just offshore.

Clarke-Fisher model - theoretical change in the relative importance of primary, secondary, tertiary and quaternary employment sectors over time as an economy develops from pre-industrial, through industrial to post-industrial stages.

Clay -a particle size classification for rock. Clay should be a rock particle with a diameter of less than 0.002mm.

Clay-humus complex -a soil particle made up of clay and some humus.

Clean Air Act, 1956 -UK legislation to control the amount of smoke produced in urban areas in response to the smog that commonly afflicted them, often for days on end.

Cleavage -the line of weakness in a rock along which it will break when put under stress.

Cliff -a tall, vertical, or near vertical, rock face.

Climate -aggregate weather conditions of an area over a long period of time which allow for the designation of seasonal patterns and expected future weather.

Climate change -long term variations in climate, particularly related to average annual temperatures and annual rainfall.

Climax community - The stage in community succession where the community has become relatively stable through successful adjustment to its environment.

Climax vegetation -the dominant and stable vegetation combination achieved naturally under particular environmental conditions over a long period of time.

Clint -flat-topped block that forms the 'paving stone' in a limestone pavement.

Clouds -visible masses of water droplets and/or ice crystals formed by condensation in the atmosphere.

Cloud seeding -attempt to create or grow clouds by the introduction of condensation nuclei in order to cause greater precipitation.

Coast -a zone of interaction of the land and the sea at the margins where the two meet.

Coastal landforms -those landforms unique to erosional and depositional processes at coasts, or due to sea level changes.

Coastal management -the attempt to mitigate the effects of erosion and flooding in coastal areas. May be hard engineering - structural features that directly block water action such as sea walls -or soft engineering -giving nature a helping hand such as beach nourishment. Some modern approaches suggest humans should intervene less in coastal environments and advocate restricted development here thus allowing coastal retreat if it happens.

Col -a saddle-like landform between mountain peaks where two corrie glaciers have back-eroded an ar 皻 e .

Cold desert -in high latitudes where temperatures are very low, there may be very arid areas due to a lack of precipitation and/or the locking of water as ice.

Cold front -the boundary between a warm and a cold air mass where the cold mass is undercutting the warm, causing the latter to rise. The rate of rise tends to be rapid causing rapid cooling and condensation which leads to the formation of tall cumulonimbus clouds and short, heavy thunderstorms.

Cold glacier -one in which ice temperature remains very low (often -30˚C) all year. The glacier will not move very rapidly if at all and so erosion is minimal.

Collective farming -an agricultural system, commonly practiced in communist countries, in which land is leased by the government to a ollective-of workers who operate the farm and, in theory, share its profits. The system was usually inefficient and often corrupted by further

government intervention. In the USSR, the collective farm, or kolkhoz, was gradually phased out after World War 2 and replaced by the state farm, or sovkhoz.

Colonialism -the establishment of direct rule by one country over another, separate country, fundamentally to improve and protect the economic situation of the dominant power.

Colonizer plants -the first plants to establish themselves in a virgin environment as the pioneer community.

Command economy -an economic system in which all decisions are made centrally by the national government, usually through the establishment of sequential five-year plans. Their express purpose is to attain fair distribution of resources among all citizens, but they are often plagued by political and economic inefficiency and corruption and many have collapsed.

Commercial farming -food production for market sale. Farmer has economic aims such as profit maximization.

Comminution -the reduction in size of particles through attrition.

Common Agricultural Policy (CAP) -the system of organization of farming in the European Union (EU). http://europa.eu/pol/agr/index_en.htm

Communication -the movement and/or exchange of information, goods and people over time and space.

Community forests -a UK policy begun in 1990 to improve derelict areas on the edge of urban areas. Landowners are given help to plant woodland on land that has fallen into disuse which is then made accessible to the local community. Aims are to improve opportunities for recreation, education and wildlife.

Commuter - a person undertaking commuting.

Commuter village -a village near to an urban area where former residents of the urban area have moved to while retaining their original jobs. As the proportion of commuters in the village increases, its character will change and there may be a decline in services as the newcomers prefer to use services in the urban area.

Commuting - movement of people between place of residence and place of work and vice versa. Can vary over space (rural-urban, intra-urban and urban-urban) and time (daily or weekly).

Comparative advantage -the idea that areas tend to be more efficient in certain economic activities than others and so should specialise in them in order to maximize their quality of life through trade.

Comparison goods -those goods which are highly priced and which are bought infrequently. Purchase decisions are usually made after comparing different brands or models etc.

Competence -in rivers, the maximum particle diameter that can be carried at a given velocity.

Competition -where more than one company provides a good or service. Can keep prices low as competitors fight for customers by undercutting their rivals. However, this could put operators out of business and reduce competition, possibly causing price increases. Can also lead to inefficiency through duplication, especially in services.

Composite volcano -one in which the cone is made up of alternating layers of lavas and ashes.

Compressing flow -in a glacier, when gradient is reduced and the ice becomes thicker and slower.

Concave slope – a slope which becomes progressively shallower downhill. It can refer to an entire slope or part of one. On a map the Contour lines will be spaced further apart with a decline in height above sea-level.

Concentric-ring model -a theory of how urban land use develops over time. Developed by Earnest Burgess in 1924 to explain social patterns in Chicago, it was later proposed as a general theory of urban land use. It says that zones of transition, low, medium and high-class residences are found in concentric rings outwards from the CBD. Since discredited as having few real-life applications due to unrealistic base assumptions that fail to account for factors such as transport routes and topography.

Condensation -the formation of water droplets or ice crystals from water vapour when it is cooled to the dew point.

Conduction -the transmission of heat through a substance i.e. through touch from a higher temperature area to one of lower temperature.

Conditional instability -when the ELR is lower than the DALR but higher than the SALR then an air mass will initially be stable and may sink. However, if the rising mechanism takes the air mass to its dew point and beyond at the SALR then the air can become instable and rise of its own accord through the release of latent heat.

Confidence level -the degree of confidence that a statistical result is the correct one rather than one produced by chance.

Confluence -where two river channels join.

Conglomerate -in physical geography, a sedimentary rock in which smooth, rounded rock pieces have been cemented into silts and clays.

Coniferous woodland -woodland or forest made up of softwood trees having common characteristics such as an evergreen appearance, waxy needle-like leaves and usually producing seeds within cones which open to allow dispersal by wind.

Connate water -water that is trapped in the interstices, or breaks, between adjacent strata of sedimentary rock. It becomes trapped at the time of deposition.

Connectivity -the extent to which points, or nodes, in a network may be interconnected and thus a measure of the network efficiency in allowing transfers in space or time. See alpha index , beta index, cyclomatic number, detour index and gamma index for measuring methods.

Consequent stream -a stream created as a consequence of uplift.

Conservative plate margin -in plate tectonics, a plate boundary where the relative movement of the two crustal plates is lateral, or past each other.

Conservation -the maintenance of a landscape (natural or man-made) in its current state.

Constructive plate margin -in plate tectonics, a plate boundary where the relative movement of the crustal plates is apart from each other allowing magma to rise from the mantle and solidify to construct new crust.

Constructive wave -a low height, low frequency wave where the net movement of material is up the beach as the swash is stronger than the backwash.

Consumer - two types:

in human geography, a person buying a good or service. In physical geography, any organism that lives off the tissue of another organism.

Containerization -the development of standardized metal containers for cargo which can be transshipped between train, lorry and ship carriers. Revolutionized haulage by reducing transshipment times and replacing large numbers of labourers with crane technology.

Continent - one of the seven largest pieces of land on earth.

Continental climate -typical climates of interior areas well away from the influence of the sea. Tend to hot summers and cold winters with a large temperature range between the two. Low overall precipitation which tends to be at its highest in summer if convection allows.

Continental crust - is the layer of granitic, sedimentary, and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as continental shelves.

Continental drift -theory that the land mass of the earth was once held as a single continent which has since split into segments which have drifted apart and into the modern configuration of the continents. Proposed by Alfred Wegener in 1912, based on observed matches in the shape of continents, their geology and biological history, it was rejected as no satisfactory mechanism could be postulated. Has regained favour, though modified, in plate tectonics theory.

Continental plate -a segment of the earth crust made up of sial. Found mostly, but not exclusively, above sea-level.

Continental shelf -shallow sea floor fringing continents. That part of the continental plate that is currently flooded due to modern sea levels.

Continuous permafrost -within the Arctic Circle average temperatures rarely rise above zero. Water in the ground generally remains frozen apart from some superficial summer melting of perhaps the top few centimeters. The permafrost can be several hundred metres deep and is not broken.

Contour interval -the difference in elevation (height above sea-level) between adjacent contour lines.

Contour line -on topographical maps, the isolines connecting points of equal height above sea-level.

C ontour ploughing - Ploughing so the furrows follow the contours of the slope i.e. they go horizontal across the slope not up and down the slope.

Contract farming -where large agribusinesses, usually food processing companies or supermarket chains, contract farmers to provide them with particular types of produce.

Conurbation -large, effectively continuous urban area produced as urban sprawl leads formerly separate settlements to coalesce.

Convection -transfer of heat in a gas or liquid by upward movement of the hotter, less dense portion. Found in atmospheric, oceanic and asthenospheric mediums.

Convection current -the circular movement of a liquid or gas undergoing convection in a limited space.

Convection plume -the upwelling part of a convection cycle in the mantle.

Convergent plate margin -see destructive plate margin.

Convex slope – a slope which becomes progressively steeper downhill. It can refer to an entire slope or part of one. On a map the contour lines will be spaced closer together with a decline in height abovesea-level.

Co-operative agriculture -smaller, individual farmers form a co-operative to reduce input costs through bulk buying and improve pricing through greater bargaining power.

Coral -a tiny animal (polyp) which exists in large colonies in warm, shallow, clear salt-water.

Coral reef -offshore accumulation of dead coral, usually with live coral on top.

Core -two main associations in geography:

in physical geography, the central interior of the earth. Thought to be an inner core, mostly solid under extreme temperature and pressure, and an outer core, mostly liquid, both composed of iron and nickel.

in human geography, an area that enjoys economic, social and political superiority in comparison to its surrounding area -the periphery or hinterland.

Core-periphery model -a model seeking to explain a spatial pattern of economic growth in which one centre or region in a country develops an economic advantage over the rest of the country. Several have been proposed.

Coriolis force -the effect of drag from the earth rotation on airflow.

Corrasion - see abrasion.

Correlation -the degree of association between two sets of data either positive -as one increases so does the other -or negative -as one increases the other decreases. Does NOT indicate causality.

Corrie - (also known as a cirque or cwm) a great bowl-shaped hollow at the head of a glacial valley. Accumulation of snow in a depression over many years forms a niche glacier which then erodes the corrie by plucking and abrasion in a rotational movement. Characterized by a steep back-wall and a rock lip at the lower, front end.

Corrie glacier -the glacier found in a corrie which has been responsible for its formation.

Corrosion - a generic term for chemical weathering.

Cottage industry -small-scale, home-based production.

Council housing -in the UK, housing funded by local government with help from central government. Started in 1919 to provide for low-paid workers and their families when forced to move due to slum clearance or when housing shortages forced prices out of reach. Housing remains in ownership of the local authority and tenants pay limited rent to it. Much of the better stock has now been transferred to private ownership.

Counterurbanisation -decentralisation of population from large urban areas to smaller ones or rural areas. Thought to be a result of both improved communication and connectivity as well as a reaction against the problems associated with large urban areas.

Crater - the depression found at the summit of a volcanic cone.

Craton - see shield area.

Creep - extremely slow downslope movement of soil. Caused by combination of factors which allow horizontal dislodging of particles which then subside under gravity. Factors include raindrop impact, soil expansion, vegetation stress and animal activity.

Cretaceous - in geologic time, a period lasting from 144m to 65m years ago.

Crevasse - a deep crack in the surface, usually in a glacier.

Cross-profile -cut away view through a feature from side to side.

Crust - solid, outer layer of the earth. Between 5 and 80km thick, it is made up of two types of material, continental or sial, and oceanic or sima which exist in large segments called plates.

Crustal plate -see crust.

Cuesta - where a more resistant strata of rock is left upstanding when less resistant strata on either side are degraded more rapidly. The dipping angle of the strata creates a steep scarp slope on one side (escarpment) and a more gentle dip slope on the other.

Cultivation -the preparation and use of land for crop growing.

Cumec - is a measure of flow rate.

Cumulative causation -the idea that one factor can trigger a sequence of events which reinforce and amplify the entire process concerned. Term coined by Myrdal to explain economic disparity between regions whereby an initial advantage in one then draws in resources to improve the position of the region at the expense of those surrounding. Also thought to work in reverse to explain economic decline.

Cuspate foreland -triangular beach form. Can be few hundred square metres to few hundred square kilometers.

Cusps - small hollows on beach fronts, a few metres across, which look like mini bays within the beach itself.

Cwm -see corrie

Cycle of poverty -the process which maintains conditions of chronic poverty in rural areas of ELDCs. A lack of money restricts, or more often precludes, investment in agricultural technology keeping yields low and thus little or no surplus for sale which maintains the lack of money.

Cyclomatic number -the number of circuits in a network.

Cyclone -extremely low pressure system. See hurricane.

Cyclonic rainfall -see depressions.

D

Dalmation coast -numerous elongated islands lying just offshore and parallel to the mainland.

DALR -see dry adiabatic lapse rate.

Dam -a large wall or earth barrier used to block a river valley. Purpose may be to store water, control flooding and/or generate electricity.

DDT -an insecticide (dichlorodiphenyltrichloroethane). It is powerful and persistent meaning it does not easily break down or disperse and can remain in the ecosystem and accumulate in organisms higher up the food chain.

Death rate - number of deaths per thousand people per year.

Debris -any fragmented rock material i.e. that produced by weathering or erosion.

Decentralization -movement of people, government functions or employment opportunities out from an established central area to a relatively peripheral one. Identified at city, regional and national scale.

Deciduous woodland -woodland or forest made up of trees which have broad, flat leaves and which shed them annually during autumn, or fall. They remain bare through the winter months when insolation is too low for efficient photosynthesis and water may be locked in snow, before growth restarts in spring.

Declination -the latitude where, on any particular day, the sun is 90˚ above the horizon at solar noon i.e. when the sun is aligned between true north and true south.

Decomposer -an organism that converts organic matter into its inorganic chemical components which are then recycled through an ecosystem. Most common ones are bacteria and fungi.

Decomposition -breakdown of organic material in the litter by detritivores. Allows the release of energy and nutrients into the soil for recycling.

Deep-sea trench -see ocean trench.

Deflation -wind removal of small, grain-size rock particles such as sand. 

Deforestation -removal of forest cover due to cutting or burning, or a combination of the two.

Deglaciation -the removal of glacier cover (glacial retreat) when ablation outstrips accumulation.

Deglomeration -the dispersal of businesses from an area due to rising costs, especially those of specialized labour and land rents. The opposite of agglomeration.

Degradation -when high discharge creates a high energy environment in a river channel leading to a lowering of the channel bed.

Deindustrialization -fall in the percentage contribution of secondary industry to an economy in terms such as value of input to GDP and importance as an employment sector.

Delta -a depositional feature found at river mouths under certain conditions. Where the river enters the body of water (sea or lake) there is energy loss and load is deposited. If the rate of deposition exceeds the rate of removal in any current within the body of water then the material will build up. As the upper surface approaches sea-level the river may be forced to split into distributary channels which remain free of further deposition. Plants may colonize the top of the deposit and help it to build up above the sea level to form new land. Three types are identified:

arcuate - a fan-shape with the 'point' at the river mouth. cuspate - a triangular shape with the 'point' facing the body of water and base at the river

mouth. bird's foot -as it suggests, with the 'toes' pointing out to the body of water.

It is now thought that the different shapes are formed according to the salinity of the body of water. High salinity means slow mixing and so the sediments flows further out across the body of water creating a cusp. Low salinity means quick mixing and deposition and so more arcuate shapes.

Demographics -the statistical characteristics of a population births, deaths, age/sex structure etc.

Demographic transition model -a theory of population change over time. Seeks to explain population increases and decreases through variations in the birth rate and death rate. Based on observations of historical changes in parts of the EMDW, it is now applied more generally though with variable levels of confidence. A major criticism is its failure to take into account changes due to migration.

Demography -the study of demographics.

Dendritic -description of a stream pattern that is random and creates a tree-like pattern.

Dendrochronology -observation of a core or cross-section of a tree trunk shows a pattern of essentially concentric rings, each representing a year of growth. The number of rings can therefore be used to date the tree. Further, wider rings (higher rate of growth) indicate wetter years, and vice versa. The study can therefore help in the construction of past climate.

Denitrification -the conversion of nitrates to nitrogen in soils by bacteria which thus leaves the soil low in nitrate and therefore less fertile.

Denudation -stripping of surface cover. Can apply to both vegetation and soils.

Dependency ratio -the proportion of working (economically active) people to non-working (non-economically active) people in a country by the formula:

            people aged 0-14 + people aged over 6 5  x 100

                               people aged 15-65

Thus suggests how many non-workers are supported by every hundred workers. While these age groups do not reflect economic status accurately, inaccuracies tend to balance out.

Dependent variable -one which is directly affected by another e.g. water temperature will vary with depth, but depth is not affected by water temperature.

Deposition -the placing down of material being transported by an agent of erosion due to a loss of energy.

Depression -weather system of the mid-latitudes, where warm, tropical air meets cold, polar air causing the tropical air to rise and thus creating an area of low pressure. Characterized by a circular pattern of isobars, a warm front, a cold front and inward blowing, anti-clockwise winds.

Deprivation -a situation where quality of life is below that of what can be expected for a particular place at a particular time.

Deprivation cycle -much the same as the cycle of poverty but as applied to EMDW inner city areas. Low wages and poverty mean overcrowding and no investment in housing. These cause poor health and stress and low levels of education and training, meaning low skill levels in the population, restricting employment opportunities and maintaining the situation of low wages and unemployment.

Deregulation -the removal of rules, regulations and laws previously imposed on an industry. Often welcomed as the removal of monopoly rights which improve competition and opportunity, they can also lead to the weakening of protection for workers and consumers.

Derelict land -land which has fallen into disuse. Most commonly applied to land that has been built on or heavily impacted by primary activities such as mining and quarrying.

Derelict land grant -in the UK, government funding for the improvement of derelict land.

Desertification -the spread of desert, or desert conditions, from an established desert area into the surrounding area. A function both of physical factors such as reduced rainfall, and human factors such as resource depletion due to increased population.

Desire line -a line on a map relating information on the movement of people by joining their point of origin with their destination. Thickness is proportional to the number of people involved in the movement.

Destructive plate margin -in plate tectonics, a plate boundary where the relative movement of the crustal plates is towards each other and where one is subducted beneath the other thus being destroyed as it returns to the mantle. The collision may be between oceanic plates or between an oceanic plate and a continental plate. The denser of the two will subduct. This will never be continental crust as it is always the less dense.

Destructive wave -a steep, high frequency wave which causes a net loss of material from the beach as the backwash is stronger than the swash.

Detour index -a measure of connectivity in a network which compares actual distance between vertices with the straight line distance.

                        DI = shortest possible actual route

                                    Straight-line distance

Detritivore -an organism which feeds on dead organic material.

Developed -an out of date term for economically more developed countries. The terminology changed to recognize that development can be measured in many different ways, not all of them linked to wealth although it is a highly important factor both directly and indirectly.

Developing -a term for a country or region that is enjoying ever increasing levels of economic development. May be an ELDC, or have moved to an intermediate stage known as newly industrialized country.

Development -use of resources, natural and human, to achieve higher standards of living. Once focused solely on economic factors, now encompasses social measures and ideas such as freedom. Can be used in general terms e.g the evel of development-or in specific terms e.g. a development project such as a power station being built.

Development area -region earmarked for economic support.

Development gap -the disparity in development between the EMDW and ELDW.

Development model -a theory of development -why and how it occurs. Two popular ones are Clarke-Fisher and Rostow.

Devonian - in geologic time, a period lasting from 408m to 360m years ago.

Dew -condensation of water directly onto ground surfaces such as leaves or car windscreens. Rapid heat loss at night causes air closest to the surface to reach its dew point.

Dew point -temperature at which air becomes saturated i.e. relative humidity is 100%.

Diastrophism -movements producing positional changes in the crust. Orogenic changes are large scale folding and faulting processes which lead to landforms such as fold mountains. Epeirogenic changes are more gentle processes of uplift.

Diffluence -the breakaway from a large glacier of a smaller, secondary flow of ice which then crosses a drainage divide. May involve uphill movement. Has important implications for post-glacial drainage patterns.

Diffusion - spread through space over time. In geography, usually applied to the uptake of an innovatory piece of technology or idea.

Dip slope - the gentle slope formed by the upper plane of the dipping, harder bed of rock in a cuesta.

Discharge - the volume of water in a channel passing a particular point in a particular time, usually cubic metres per second or cumecs. Calculated by multiplying cross-sectional area of the river by its velocity.

Discontinuous permafrost -between 50˚N and the Arctic Circle where mean annual temperature is -1˚ to -5˚ there will be patches of permanent permafrost perhaps 50 metres deep, separated by areas of little or no permafrost which are kept warmer by local conditions such as rivers.

Discordant coast -a coast of headlands and bays where the different rock types are perpendicular to the coastline.

Discrete variable -a variable which can only be measured in whole, individual units if it is to have any real meaning e.g numbers of people.

Diseconomies of scale -at large-scale levels of output inefficienies may creep in and cause unit costs to rise.

Dispersal - the movement of people or organisms from their area of birth.

Disposable income -income left after taxes and necessities have been paid. This can be spent on goods or services wanted, or saved.

Dissolved load -those minerals that have been taken into solution and are carried along by a river.

Distance decay -the negative correlation of distance to interaction between two points i.e. the greater the distance, the lower the amount of interaction.

Distance ratio -gradient of a slope measured by dividing vertical change by horizontal change. Expressed as a percentage or a ratio.

Distributary -a stream which splits away from the main channel and never rejoins it. Common across deltas as they are so close to the sea that the channel has no space to find its way back. When a channel does rejoin the main stream, it is braided.

Distribution -two uses:

movement of goods from producers to places where they are sold. spatial pattern of where an observed feature appears within a particular area.

Distribution channel -the route a product takes from producer to consumer. Becomingly increasingly direct as producers offer products direct through the internet.

Diurnal - in geography, daily, or of each day, where a day means the full 24 hour period.

Divergent plate margin -see constructive plate margin.

Diversification -a strategy for spreading business risk whereby a business branches into new industries or markets to protect against potential, unpredictable problems in their core business.

Doldrums - see intertropical convergence zone.

Dormitory settlement -a rural settlement that is increased in size due to the influx of new residents from a nearby urban area. Incomers may be retiring or 'escaping' the negative aspects of city life while retaining jobs in the urban area to which they commute. Often leads to a decline in services as the incomers have private transport and spend most of their income in the urban area.

Doubling time -number of years taken for a population to double in size (number).

Downward spiral -decline occurring in a vicious circle or negative cumulative causation.

Draa -vast desert sand dune large enough to carry smaller dunes across its surface.

Drainage basin -the area from which a river channel receives water.

Drawdown -the change in the level of the upper water surface in a well or reservoir which is due to the withdrawal of water.

Dredging - removal of sediment from the bottom of a sea or river. Carried out to improve navigation or to obtain material for construction uses and beach nourishment.

Drift - material deposited by glacial and fluvioglacial processes.

Drought -a lack of precipitation into an area for a long period of time. Modern droughts are thought to be intensified by population pressure which may help to remove water available for local evaporation.

Drumlin -a mound of glacial debris formed into a smooth, elongated feature whose apex is skewed towards the rear (in terms of the direction of movement). The steeper slope at the back of the feature is called the stoss end. Origin still being debated. Thought to be the result of deposition followed by erosion/shaping.

Dry adiabatic lapse rate (DALR) -the rate of fall in air temperature by adiabatic change as unsaturated air gains altitude. Approximately 1 蚓 per 100m.

Dry valley -valley, usually found in upland areas of limestone or chalk, demonstrating the characteristics of a typical upper course river, but containing no river.

Dual economy -a country having one or two core areas which far outstrip the development of the surrounding peripheral area.

Dumping - large-scale selling of a good in another country at below-cost price to earn foreign currency, get rid of excess production or attack that country domestic producers.

Dune - ridge or mound of sand formed by wind conditions in arid and coastal areas.

Dust bowl - in the USA, the area of degradation of the agricultural land of the High Plains region in the 1930s when overexploitation of the land exposed the area to a higher impact when drought arrived. Drove many farmers from the land. Modern ideas, methods and technology have since led to recovery.

Dyke - three meanings:

a wall or embankment constructed parallel to the coast to protect against flooding. a ditch in a fenland area a wall-shaped intrusion of magma which cuts across bedding planes.

Dynamic equilibrium -lack of change in a system as inputs and outputs remain in balance. If changes do occur, then feedbacks will allow for correction.