Geoscience Reference
In-Depth Information
Vivipary
Plant reproduction by the formation of bulblets
on the parent.
Volcanic arc
An arcuate line of explosive, andesitic island
volcanoes erupted through oceanic crust on the landward
side of a
B-subduction zone
as a result of the hydration and
partial melt of downgoing crust; the arc may eventually
migrate and weld on to adjacent continental crust.
Volcanic breccia
A
pyroclastic
rock formed of consoli-
dated, angular volcanic rock rubble.
Wadati-Benioff subduction
The full title of what is more
commonly known as
Benioff
or
B-subduction
.
Water balance
The volumetric input, storage and output
of water which constitutes the water budget of a
drainage
basin
per unit time, normally a calendar year.
Water-holding capacity
The amount of water held in soil
after free drainage under the influence of gravity.
Water-layer weathering
Rock weathering in the
inter-
tidal zone
by those processes of
slaking, hydration
and
salt
weathering
which are enhanced by regular cyclic hydration
and drying.
Watershed
The delimiting boundary of a
drainage basin
,
normally at the land surface but taking into account any
lateral underground transfers determined by geological
conditions; alternatively, the
drainage basin
delimited by
such a boundary.
Wave
An oscillatory rise and fall in a water surface,
marking the horizontal transmission of wind-driven
energy through the orbital motion of water particles.
Wave base
The water depth at which the orbital motion
of surface waves ceases.
Wave period
The time taken for consecutive wave crests
to pass a fixed point.
Wave train
A regular procession of water surface waves
characterized by their
wavelength
and
wave period
.
Wave-cut notch
A notch or indentation cut into the
base of a cliff by wave action.
Wavelength
The distance between crests or troughs of
adjacent
waves
.
Weathering
The progressive alteration and eventual
chemical or mechanical disintegration of rock mass at the
land surface; exposure to a different thermal and moisture
environment from that in which it formed renders it
unstable and susceptible to weathering.
Weathering rind
An outer crust of discoloured and
texturally altered rock representing the initial stage in
rock weathering.
Weathering solution
Solution containing metallic ions
and silica which is produced during weathering.
Wedge slide
Sliding failure of a rock wedge bounded by
two release surfaces where two
planar discontinuities
intersect; the angle of intersection must be greater than
the internal friction angle of the mass but less than the
parent slope angle.
Wetted perimeter
The length of a river channel covered
by water at a particular point and water depth; an
important component of the measure of
hydraulic radius
and
efficiency
.
White alkali soils
A popular term for solonchaks.
White box
A system in which a detailed knowledge of
all the internal structure is identified; it is rarely achieved,
except in the simplest of systems.
Wildfire
A fire started by humans either by accident or
for malicious reasons.
Wilson cycle
The alternative name for the superconti-
nental cycle, named after its proponent, J. Tuzo Wilson,
during the 1960s.
Wilting point
The moisture content of soil at which
there is insufficient water to maintain the turgor of the
plant.
Wind stress
The force exerted by wind per unit area on
an adjacent surface.
Windstorm
A violent cold-air gravity flow off the eastern
Rocky Mountains in winter, stimulated by temperature
inversion over snow.
Xerophyte
A plant adapted to grow in arid habitats.
Xerosere
A
primary succession
which starts on a surface
suffering from drought.
Yardang
An exposed rock surface abraded into a
streamlined shape by windblown sand.
Younger Dryas
A European term for the climatic
deterioration and mountain glaciation
c.
11,000-10,000
BP
, known in Britain as the
Loch Lomond stadial
.
Zeolite
The lowest grade of metamorphic rock, formed
at relatively low lithospheric pressures and temperatures.
Zonal
Soils occurring in extensive zones on a world
scale; winds blowing from west to east or vice versa.
Zone of soil formation
The upper part of the zone of
weathering
where
soil-forming processes
are most active.
Zone of weathering
The upper part of the lithosphere
where weathering processes are operating at a maximum.
.
