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.
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.
Acid lava - lavas containing high percentage of silica. Tend to have high melting points and to be highly viscous.
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.
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.
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:
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 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.
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.
Antecedent drainage - the maintenance of course by an old river over more recent uplifting of the land surface.
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.
Arable - cultivation of crops such as cereals, legumes, roots and leaves.
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.
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).
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.
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.
Autotroph - an organism that can produce nutritional organic substances from simple inorganic substances. Thus, plants grow by synthesizing carbon dioxide and water using sunlight.
BOUNDARY, n. In political geography, an imaginary line between two nations, separating the imaginary rights of one from the imaginary rights of the other.