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A - Abiotic to Azonal soil - Geography Dictionary

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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, calvingevaporationsublimation 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.

Adaptation - management strategies which involve allowing the perceived problem to continue and changing our behaviour to incorporate the resulting change.

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 cyclomaticnumber 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 intermediatetechnology) 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.

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