Geoscience Reference
In-Depth Information
trace element
element that occurs at a concentration of less than 1%.
trench
long, narrow arcuate depression in the seabed, which results from the bending of the
lithospheric plate as it descends into the mantle at a subduction zone.
triple junction
point where three plates meet.
ultramafic rock
rock ultra-rich in magnesium (
ma
) and iron (
fic
) minerals such as olivine
and pyroxenes.
unconformity
rock strata above an unconformity, which were deposited or extruded at a
much later time, or after erosion or deformation, upon the strata beneath; marks a break or gap
in the geological record.
vector
quantity having both magnitude and direction.
velocity
vector quantity that indicates both the speed and the direction in which a body is
moving.
viscoelastic material
a material that can behave as an elastic solid on a short timescale and
as a viscous fluid on a long timescale.
viscosity
resistance to flow within a fluid; a measure of the internal friction of the fluid, also
known as dynamic viscosity; the unit of viscosity is N s m
−
2
=
Pa s; symbol,
η
;
see also
kinematic viscosity.
volatiles
chemical components that go into a vapour phase during igneous and metamorphic
processes (e.g., water, CO
2
).
volcanic rock
igneous rock that solidified at the Earth's surface.
volcanism
geological process that involves the eruption of molten rock.
wavefront
imaginary surface or line that joins points at which the waves from a source are in
phase (e.g., all at a maximum or all at a minimum).
wavelength
distance between one crest of a wave and the next; usual symbol,
λ
.