aa
Volcanic lava rock that is thick and porous and has a rough, jagged surface when it cools. It is a Hawaiian word, pronounced ah‐ah.
abandoned well
Any well that has not been used for a long time and/or is not properly sealed, and is so poorly maintained that it cannot be used for the purpose for which it was intended.
ablation zone
The zone of a glacier in which losses through various processes, such as calving, deflation, melting, etc., exceed any addition through snowfall or accumulation of rime ice. Compare accumulation zone.
absolute chronology
A chronology that determines the age of a feature or event in years. Contrast relative chronology.
absolute humidity
The amount of water vapour in air, determined as the mass of vapour per unit mass of air, and normally given in grams per cubic metre. See also humidity; specific humidity.
absolute poverty
An extreme state of poverty, in which the standard of living is below the minimum that is needed for the maintenance of life and health. Contrast relative poverty.
absolute relief
The maximum elevation of a particular area above sea level. Contrast relative relief.
absolute scarcity
A condition that exists when there is not enough of a resource in existence to satisfy existing demand for it. Contrast relative scarcity.
absorb
To take something in (such as the penetration of a solid substance by a liquid, by capillary, osmotic, solvent, or chemical action). In energy terms, to take in energy and then not reflect it.
absorbed dose
The amount (dose) of a chemical substance that is absorbed by, and thus enters the body of, an organism exposed to it. Most commonly expressed as milligrams per kilogram body weight per day (mg ...
absorption
1 The penetration of one substance into or through another, such as the absorption of water into soil, or the uptake of water and nutrients by a cell or organism which absorbs them. Contrast ...
absorptive capacity
The maximum amount of waste material that can be naturally absorbed by the environment on a sustainable basis, without causing environmental damage.
abstraction
The action of removing something, such as the abstraction of water from a river, lake or groundwater, for use in industry. Also known as extraction, particularly when applied to a rock or mineral.
abyssal hill
Relatively small topographic features of a dominantly flat, deep-ocean floor, commonly 50–250 m in height and a few kilometres in width. They are most typical of the Pacific Ocean floor at depths of ...
abyssal plain
Smooth, almost level area of the deep-ocean floor in which the gradient is likely to be as low as 1:10 000. The covering sediments are usually thin deposits of a pelagic ooze or distal turbidite.
abyssal zone
The lower depths of the ocean (below approximately 2000 metres), where there is effectively no light penetration. Abyssal organisms are adapted for living under high pressures in cold dark ...
accelerated erosion
An increased rate of erosion above natural levels. This can be natural (for example, caused by hurricane damage) but is often caused directly or indirectly by human activities. It removes soil much ...
acceptable risk
The level of risk that is regarded as acceptable by the community or authorities, below which no specific action by local government is deemed necessary other than making the risk known. Contrast ...
