A. Penck
(1858–1945)A German mineralogist from the University of Berlin, Penck's main interest was in Quaternary glacial land-forms, which he classified according to shape. Some of his work was done in ...
Aalenian
A stage in the European Middle Jurassic (175.6–171.6 Ma, Int. Commission on Stratigraphy, 2004). See also dogger.
abandonment facies association
A facies association formed under conditions of rising sea level, when clastic deposition has ceased and sediment is deposited very slowly.
abiotic
Not living, non-biological, usually describing factors in an ecosystem: atmospheric gases, humidity, salinity, soil mineral particles, water, and so on. An abiotic environment is one without any ...
ablation
The removal of surface snow or ice by sublimation, melting, or evaporation. The term is sometimes extended to include snow removed by the wind (deflation) and also the calving of glaciers.
Abraham Gottlob Werner
(1749–1817)Professor of mineral science at the Mining Academy, Freiberg, who developed a system of mineral classification which he called ‘oryctognosy’, based on the external characteristics of ...
abrasion
The erosive (see erosion) action that occurs when rock particles of varying size are dragged over or hurled against a surface. Some common agents of abrasion are the bed load of streams, rock debris ...
abrasion ramp
A gentle, seaward slope, with a gradient of approximately 1∘, in an intertidal shore platform that is caused by wave abrasion. The removal of material by wave action leaves the base of the cliff ...
abrasion terrace
A former shore platform, now above sea level, either through tectonic uplift of the mainland, or eustatic lowering of sea level—and thus indicative of an emergent coastline. See Hanß in A. Alsharhan ...
abroholos
A violent squall, particularly prevalent in summer, that occurs off the south-eastern coast of Brazil.
absolute drought
In the UK, a period of fifteen days on none of which more than 0.25 mm of rain falls. National definitions vary with climate; in Libya, droughts are recognized only after two years without rain. ...
absolute instability
The state of a column of air that has a lapse rate that everywhere exceeds the dry adiabatic lapse rate. The column is therefore unstable throughout its height.
absolute plate motion
The movement of a crustal plate in relation to a fixed point, such as a hot spot. See Gripp and Gordon (1990) Geophys. Res. Letts 17 for calculations of absolute plate ...
absolute stability
The state of a column of air that has a lapse rate that is always less than the saturated adiabatic lapse rate and thus remains stable at all levels. See stability.
absorptance band
The range of wavelengths of electromagnetic radiation which are absorbed by a material. See also absorptance.
absorption
The amount of seismic energy lost during transmission, by conversion to heat. The absorption coefficient is the fractional loss of energy over a distance of one wavelength; hence higher-frequency ...
absorption, atmospheric
The various components of the Earth's atmosphere act to reduce or completely block certain wavelengths of the radiation incident at upper levels. The principal active atoms are oxygen and nitrogen, ...
abstraction
The selection and conceptualization of a phenomenon, or some aspect of it; a way of viewing a real world object, usually a simplification—such as a model. Data abstraction captures the essential ...
