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Glossary of Terms: U
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- Ultisols
- Soil order
(type) of the United States
Natural Resources Conservation Service Soil Classification
System. Tropical or subtropical soil that
is in an advanced state of development. These soils
have pronounced eluviation, clay accumulation
in a subsurface layer, and are often poor in base cations.
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- Ultramafic
- Rock that
is rich in magnesium and iron content.
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- Ultraviolet Radiation
- Electromagnetic
radiation with a wavelength between 0.1
and 0.4 micrometers (µm).
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- Unconfined Aquifer
- Aquifer that
is not restricted by impervious layers of rock.
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- Unconfined Groundwater
- Groundwater that
is not restricted by impervious layers of rock.
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- Unconformity
- A break in the sequence of sedimentary strata.
Often the unconformity surface is the result of erosion.
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- Undercut Bank
- Steep bank found on the inside of stream
meanders. Formed by the erosion that
occurs when a stream channel moves horizontally.
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- Uniformitarianism
- Is a theory that rejects the idea that catastrophic forces were responsible for the current conditions
on the Earth. The theory suggested instead, that
continuing uniformity of existing processes were
responsible for the present and past conditions
of this planet.
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- United States Natural
Resources Conservation Service Soil Classification
System
- A hierarchical system that is used in United States
to classify soils.
This system has six levels: order, suborder, great
group, subgroup, family,
and series.
At the order level,
12 types of soils are recognized: gelisols, oxisols, aridsols, mollisols, alfisols, ultisols, spodsols, entisols, inceptisols, vertisols, histosols,
and andisols.
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- Universal Time (UT)
- The mean solar time of the meridian at the Prime
Meridian. Universal Time replaced the
time standard known as Greenwich
Mean Time in 1928. Universal Time is
commonly used to denote solar time.
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- Universal Transverse
Mercator (UTM) Grid System
- Rectangular coordinate
system used to find location of points
on the Earth's surface. Based on the Universal
Transverse Mercator projection system.
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- Universe
- All of the observable phenomena in the celestial cosmos.
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- Unloading
- The releasing of downward pressure on rocks because
of removal of overlying material by erosion.
Unloading can cause the development of horizontal
bedding in once solid rock.
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- Unstable Atmosphere
- Condition in the atmosphere where
isolated air parcels have a tendency to rise. The
parcels of air tend to be warmer than the air that
surrounds them.
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- Unstable
Equilibrium
- In an unstable equilibrium the system returns
to a new equilibrium after disturbance.
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- Updraft
- Upward movement of air.
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- Upper Air Westerlies
- Consistent winds that
exist in the upper troposphere that
flow east to west from about 20° of latitude
to the poles.
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- Upper Mantle
- Layer of the Earth's interior extending from the
base of the crust to
670 kilometers below the surface. Part of the Earth's mantle layer.
The upper mantle is composed of peridotite,
an ultramafic magma primarily
made up of the minerals olivine and pyroxene.
The top layer of the upper mantle, 100-350 km below
surface, is called the asthenosphere.
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- Upslope Fog
- Fog produced
by air flowing over topographic barriers. As the
air is forced to rise, it is cooled by adiabatic expansion.
Upslope fog is most common on the windward slopes
of hills or mountains.
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- Upwelling
- The movement of nutrient-rich deep seawater to
the ocean's surface.
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- Urban Area
- Geographic area with a high density of people over
a limited area. Homes and other types of buildings
tend to be close together. Urban systems also tend
to differentiate themselves spatially into particular
types of human activities.
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- Urban Heat Island
- Observed condition that urban areas tend to be
warmer than surrounding rural areas.
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- Urbanization
- Expansion of cities into rural regions because
of population growth. In most cases, population growth
is primarily due to the movement of rural based people
to urban areas. This is especially true in Less
Developed Countries.
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Citation: Pidwirny,
M. (2006). "Glossary of Terms: U". Fundamentals of Physical Geography,
2nd Edition. Date
Viewed. http://www.physicalgeography.net/physgeoglos/u.html |
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