Geoscience Reference
In-Depth Information
Trade Winds.
Winds on the equatorial side of mobile polar
cells, blowing from east to west within 20-30° of the
equator. Their steadiness for three to four months of
the year greatly benefited trading ships in the days of sail.
Trench.
An area of oceanic crust that has been dragged
downward by the movement of oceanic crust beneath
a continental plate.
Tropical Cyclone.
A large-scale vortex of rising air
hundreds of kilometers in diameter that forms over the
tropical oceans. It is characterized by copious rain and
a central area of calm surrounded by rotating winds
blowing at speeds in excess of 200-250 km hr
-1
.
Tropopause.
The band separating the troposphere -
where temperature decreases with altitude - from the
stratosphere - where temperature increases with
altitude. It forms a barrier to the ready exchange of air
between these two zones.
Troposphere.
The lower part of the atmosphere,
10-12 km in altitude, characterized by cloud formation
and a drop in temperature with elevation.
Tsunami.
A Japanese word for 'harbor' (tsu) 'wave'
(nami). It is used to define a water wave generated by
a sudden change in the seabed resulting from an
earthquake, volcanic eruption, or landslide.
Tsunami Earthquake.
Some earthquakes that are
normally too small to produce any sea waves locally
generate devastating and deadly tsunami.
Turbulence.
Flow - also called turbulent flow - in which
individual particles or molecules travel unpredictable
paths apparently unaffected by gravity.
Vertical Aggradation.
The build-up of a floodplain in a
vertical direction because of the deposition of sediment.
VHF.
Abbreviation for 'very high frequency'. That part
of the electromagnetic spectrum with a wavelength
between 30 and 300 megahertz, characteristic of radio
and television transmission.
Victim-Helper Relationship.
In disasters where survivors
are at the mercy of outside support for survival for their
daily requirements, a strong dependence can develop
between a victim and those who are providing the aid.
This dependency may not be easily terminated when
the necessity for relief has ended.
Viscosity.
The resistance of a fluid to the motion of its
own molecules because they tend to stick together.
Voids.
The spaces or gaps that exist between particles in
a sedimentary deposit, filled with air or water.
Vortex.
A spinning or swirling mass of air or water that
can reach considerable velocity.
W
Walker Circulation.
The normal movement of air across
the tropical Pacific is from the east, between a stationary
high-pressure cell off the coast of South America, and a
low-pressure zone over Indonesia-India. In the 1920s,
Gilbert Walker discovered that the strength of this air
movement determined the intensity of the Indian
monsoon.
Wave Diffraction.
The tendency for wave energy to spread
out along the crest of a wave. Hence, when a wave
passes through a narrow harbor entrance, the wave will
spread out to affect all the coastline inside a harbor.
Wave Refraction.
The tendency for the velocity at which
a wave travels to reduce over shallow bathymetry.
Hence, a wave crest tends to wrap around headlands
and to spread out into bays.
Wave-rider Buoy.
An instrument, consisting of sensitive
accelerometers encased inside a buoy and floating on
the ocean surface, used for measuring the height and
energy of waves.
Wind-Chill Factor.
The factor by which the temperature
of a surface is reduced because of the ability of wind
to remove heat from that surface more efficiently by
convection (see Figure 3.23).
Wind Shear.
The tendency for winds to move at different
velocities with elevation because of strong temperature
differences. The wind, as a result, may accelerate in
speed over short altitudes or even change direction - a
particularly hazardous situation for airplanes landing or
taking off.
U
Ultrasound.
Sound with a frequency above 20 000
vibrations per second and generally not perceivable by
the human ear.
Uniformitarianism.
A geological explanation developed in
the eighteenth century to counteract the Catastrophists.
It involves two concepts: the first implies that geological
processes follow natural laws applicable to science
(methodological uniformitarianism); the second implies
that the type and rate of processes operative today
have remained constant throughout geological time
(inductive reasoning).
V
Van Der Waals' Bonds.
The weak attraction exerted by all
molecules to each other, caused by the electrostatic
attraction of the nuclei of one molecule for the electrons
of another.
