Glossary - Discovering Physical Geography - page 582

shale play A geographic area, dominated by shale bedrock,
that is targeted for exploration due to favorable geological
conditions that suggest high potential to yield an economic
quantity of oil or natural gas. 562
shield volcano A very broad volcano with shallow slopes
that forms in association with nonviscous lava flows. 364
shortwave radiation The portion of the electromagnetic
spectrum that includes gamma rays, X-rays, ultraviolet radia-
tion, visible light, and near-infrared radiation. 60
sinkhole A topographic depression that forms when
underlying rock dissolves, causing the surface to
collapse. 404
slip face The steep slope that lies on the leeward side of a
sand dune at the angle of repose. 490
slope The degree of steepness of a portion of the
landscape. 251
slump A mass-wasting process in which rock and sediment
rotate and move down the slope along a concave plane relative
to the surface. 384
small circles Circles that intersect the Earth's surface and
that do not pass through the center of the planet. 15
small-scale map A map that shows a relatively large
geographic area with a relatively low level of detail. 27
soil The uppermost layer of the Earth's surface that forms by
the influence of parent material, climate, relief, and chemical
and biological agents. 266
soil creep The gradual downhill movement of soil, trees,
and rocks due to the force of gravity. 383
soil-forming factors The variables of climate, organisms,
relief, parent material, and time that collectively influence the
development of soil. 271
soil horizons The distinct layers within a soil that result
from pedogenesis. 280
soil order A group of 12 distinctive soils differentiated at the
most general level. 283
soil profile A vertical exposure in which all soil components
can be seen. 280
soil salinization The process in which soils become en-
riched in soluble salts such as sulfates from calcium and
potassium. 549
soil science The study of soil as a natural resource through
understanding of its physical, chemical, and biological
properties. 283
soil structure The way soil aggregates clump to form dis-
tinct physical characteristics. 277
soil taxonomy The method of soil classification that is
based on the physical, chemical, and biological properties of
the soil. 283
soil-water budget The balance of soil water that involves
the amount of precipitation, evapotranspiration, and water
storage and loss.

solar constant The average amount of solar radiation
(~1370 W/m2) received at the top of the atmosphere. 61
solar noon The time of day when the Sun angle reaches its
highest point as the Sun arcs across the sky. 53
solifluction A form of soil creep that occurs in arctic
environments where freeze-thaw processes result in lobes of
soil moving gradually downslope. 383
solum The A, E, and B horizons of a soil, which form
through pedogenic processes.

281

The half of Earth that lies south of

southern Hemisphere

the Equator. 15
spatial analysis A method of analyzing data that specifical-
ly includes information about the location of places and their
defining characteristics. 5
spatial resolution The area on the ground that can be
viewed in detail from the air or space. 34
specific humidity The measurable amount of water vapor
that is in a definable body of air. 143
spit A linear bank of land that extends into a bay made by
the deposition of longshore sediment. 520
spodic horizon A mineral soil horizon characterized by
the illuvial accumulation of aluminum, iron, and organic
carbon. 290
spodosols Soils in cool, humid regions that form through
podzolization and contain a spodic horizon enriched in eluvi-
ated iron, aluminum, and organic carbon. 290
spring Equinox Assuming a Northern Hemisphere seasonal
reference, the Spring (or vernal) Equinox occurs on March
20 or 21, when the subsolar point is located at the Equator
(0°). 51
stable air A body of air that has a relatively low environ-
mental lapse rate compared to potential uplifting air; thus,
strong convection cannot occur. 162
stationary front A boundary where contrasting air masses
are flowing parallel to one another. 171
stratopause The upper boundary of the stratosphere where
temperature reaches its highest point. 88
stratosphere The layer of the atmosphere, between the
troposphere and mesosphere, that ranges between about 12 km
and 50 km (between ~7.5 mi and 31 mi) in altitude. 88
stratus clouds Layered sheets of clouds that have a thick
and dark appearance. 153
stream hydrograph The graphical representation of stream
discharge over a period of time. 417
strike-slip fault A structural fault along which two litho-
spheric plates or rock blocks move horizontally in opposite
directions and parallel to the fault line. 352
subduction The process by which one lithospheric plate is
forced beneath another. This usually happens when oceanic
crust descends beneath continental crust, but it can occur
where two plates of oceanic crust meet. 268 341