Environmental Engineering Reference
In-Depth Information
Planar slide A sliding failure along a single planar discontinuity , inclined at an angle
less than that of the slope on which it occurs but greater than the internal friction angle
of the material.
Plant community A group of plants which form a distinct combination of species in the
landscape and which interact with each other.
Plant uptake The amount of a nutrient absorbed by a plant, or the process of the
absorption.
Plastic A condition in which material is capable of continuous and permanent
deformation without fracturing.
Plastic limit The threshold water content of a solid sediment at the point at which its
behaviour changes to aplastic state.
Plate A large and rigid 'raft' of Earth's lithosphere which is mobilized by mantle
convection currents and whose boundaries are marked by the formation or destruction
of oceanic crust and the creation of new continental crust.
Plate tectonics The global-scale movement and deformation of Earth's lithospheric
plates, representing the surface expression of Earth's long-term geological evolution
and responsible for global-scale landforms.
Platy A type of soil structure consisting of horizontal units.
Playa An enclosed, ephemeral lake basin and its residual mud or evaporite floor in an
arid or semi-arid environment.
Pleistocene The first epoch of the Quaternary period, which lasted from 1ยท8 million to
10,000 years before the present time, and when Earth's glaciers frequently covered
double their present area.
Plinthite A reddish clay in tropical and subtropical soils which hardens irreversibly on
drying; it consists of sesquioxides of iron and aluminium, and kaolinite .
Pluton An igneous intrusion of plutonic character which has cooled and solidified below
ground.
Plutonic Said of igneous rock mass formed at great depth in the lithosphere by slow
cooling, and characterized by granitic texture and mineralogy.
Polar glacier See cold glacier .
Pollen analysis The technique of reconstructing vegetation covers of the past by studying
the pollen grains and spores of plants preserved in oxygen-deficient peats, sediments
and soils.
Pollen diagram An important graph used in pollen analysis , which plots the frequency of
the pollen grains or spores of specific types of plant against the depth (i.e. time or
sequence) of their occurrence in peat, soil or sediment.
Polyclimax theory The theory of climax vegetation which emphasizes that in any region
a variety of climaxes will develop in relation to soil and topographic conditions.
Polymerization The formation of large framework minerals by the replication of smaller
constituent minerals, involving the sharing of atoms and consequential strengthening
of mineral structure.
Polymorphic The description of a single mineral capable of assuming two crystalline
forms.
Polyploidy A genetic adaptation in plants, endowing them with more than two sets of
chromosomes, which appears to make them particularly vigorous and successful
colonizers of hostile environments.
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