Glossary - Discovering Physical Geography - page 584

Ultisols Mineral soils in subtropical environments that
formed through laterization and thus are depleted of calcium
and have an argillic horizon. 287
United states Public land survey The primary way that
land is subdivided in the United States by using a grid system
based on the four cardinal directions. 19
Unsaturated zone The area between the soil-water belt
and the water table where pore spaces are not saturated with
water. 392
Unstable air A body of air that has a relatively high envi-
ronmental lapse rate compared to uplifting air within it; thus,
strong convection can occur. 162
Updrafts An area of rapidly flowing air that is moving up-
ward within a thunderstorm. 184
Upwelling current A current that ascends to the surface of
the ocean because water temperature increases and salinity
decreases. 132
Urban heat island The relatively warm temperatures
associated with cities that occur because paved surfaces and
urban structures absorb and release radiation differently from
the surrounding countryside.

Wave amplitude The overall height of any given wave as
measured from the wave trough to the wave crest. 60
Wavelength The distance between adjacent wave crests or
wave troughs. 60
Wave refraction The process through which waves are
focused and bent around headlands. 515
Waves Oscillations in a body of water that form mostly due
to the frictional force generated by wind blowing across the
surface of the water. 511
Weather Day-to-day changes that occur in temperature and
precipitation. 202
Weathering Physical or chemical modification of rock or
sediment that occurs over time. 372
Westerlies Midlatitude winds that generally flow from west
to east. 119
Wet adiabatic lapse rate (WAr) The rate at which a satu-
rated body of air cools as it lifts. The average rate is about
5°C/1000 m (2.7°F/1000 ft). 151
Wilting point The threshold amount of soil water below
which plants can no longer transpire water. 268
Wind abrasion Erosion that occurs when rock is ground,
smoothed, or polished by the wind in a manner similar to
sandblasting. 487
Windward side The side of a mountain range that faces
oncoming winds. 129
Winter solstice Assuming a Northern Hemisphere seasonal
reference, the Winter Solstice occurs on December 21 or 22,
when the subsolar point is at the Tropic of Capricorn
(23.5° S).

101

V
Valley breeze Upslope airflow that develops when mountain
slopes heat up due to re-radiation and conduction over the
course of the day. 129
Variable gases Atmospheric gases such as carbon dioxide,
water vapor, and ozone that vary in concentration in space and
time. 63
Ventifact An individual rock that is pitted, grooved, or
streamlined through wind abrasion. 487
Vertical zonation The change in environmental characteris-
tics that occurs with respect to altitude. 252
Vertisols Soils that contain an abundance of expandable
clay and thus swell and shrink during wet and dry cycles,
respectively. 288
Volcanic arc A chain of volcanoes created by rising magma
derived from a subducting tectonic plate. 361
Volcano A mountain or large hill containing a conduit that
extends down into the upper mantle, through which magma,
ash, and gases are periodically ejected onto the surface of
Earth or into the atmosphere.

53

X

Xerophytic plants Plants in very dry places that have a num-
ber of survival mechanisms in response to prolonged periods
of drought.

249

y
yardangs Ridges that are sculpted and streamlined by wind
abrasion and deflation.

487

360

Z

W
Warm front A frontal boundary where warm air is advancing
into relatively cool air. This front is typically associated with
slow, steady precipitation. 171
Water rights Legally protected rights to take possession of
water occurring in a natural waterway and to divert that water
for beneficial purposes.

Zonal flow Jet stream pattern that is tightly confined to the
high latitudes and is thus circular to semicircular in polar
view. 121
Zone of ablation The part of a glacier where melting ex-
ceeds snow accumulation. 449
Zone of accumulation The geographical area where snow
accumulates and feeds the growth of a glacier.

543

The top of the saturated zone. 393 449 Water table