D Flashcards
DALR
See dry adiabatic lapse rate.
Dalmation coast
Numerous elongated islands lying just offshore and parallel to the mainland.
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:
1. Arcuate - a fan-shape with the ‘point’ at the river mouth.
2. Cuspate - a triangular shape with the ‘point’ facing the body of water and base at the river mouth.
3. 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’s 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 >65 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.