Glossary - Discovering Physical Geography - page 578

l
lagoon A brackish body of water that lies behind a bay-
mouth bar. 521
land breeze Nighttime circulatory system along coasts
where winds from a zone of high pressure over land flow to a
zone of relatively low pressure over water. 129
land cover The various things that cover the landscape,
such as forests, roads, and water bodies, at any point in
time. 569
landform A natural feature, such as a hill or valley, on the
surface of Earth. 342
landslide An instantaneous movement of soil and bedrock
down a steep slope in response to gravity, triggered by an
event such as an earthquake. 384
large-scale map A map that shows a relatively small
geographic area with a relatively high level of detail. 27
latent heat Heat stored in molecular bonds that cannot be
measured. 74
laterization A regional soil-forming process in tropical and
subtropical environments that results in extensive eluviation of
minerals except for iron and aluminum. 286
latitude The part of the Earth's grid system that determines
location north and south of the Equator. 15
laurentide Ice sheet The continental glacier that covered
eastern Canada and parts of the northeastern United States
during the Pleistocene Epoch. 466
lava dome A steep-sided volcanic landform consisting of
highly viscous lava that does not flow far from its point of ori-
gin before it solidifies. 361
leeward side The side of a mountain range that faces away
from prevailing winds. 129
level of condensation The altitude at which water changes
from the vapor to liquid phase. 151
limestone Sedimentary rock consisting of over 50% cal-
cium carbonate (CaCO 3 ). 316
liquid outer core The outer part of the Earth's core. This
area is about 2250 km (1400 mi) thick and consists of molten
iron and nickel. 307
lithification The process whereby sediments are cemented
through compaction to form rock. 313
lithosphere The outer, solid part of Earth that is about 70
km (44 mi) thick and includes the uppermost part of the asthe-
nosphere and the crust. 308
littoral drift Sediment that is transported through the com-
bined processes of longshore drift and beach drift.

longitudinal profile A graph that illustrates the change in
stream gradient in cross section along a stream from its source
to its mouth. 424
longshore current The current that develops parallel to a
coast when waves approach the coast obliquely and forward
momentum is deflected. 513

longshore drift

Transport of sediment by the longshore

current. 513
longwave radiation The portion of the electromagnetic
spectrum that includes thermal infrared radiation. 60
low-pressure system A rotating column of air where air
converges at the surface and subsequently lifts. 108
low-pressure trough An elongated area of depressed air
pressure in the upper atmosphere that is typically associated
with cloudy skies and rain. 176
low latitudes The zone of latitude that lies between about
35° N and 35° S. 17

M
Magma Molten rock beneath the surface of Earth. 311
Mantle The layer of the Earth's interior that lies between
the liquid outer core and the crust. This area is about 2900 km
(1800 mi) thick and consists largely of silicate rock. 307
Map projection The representation of the three-dimensional
Earth on a two-dimensional surface. 23
Map scale The distance ratio that exists between features on
a map and the real world. 27
Maritime A place that is close to a large body of water that
moderates temperature. 94
Maritime vs. continental effect The difference in annual
and daily temperature that exists between coastal locations and
those that are surrounded by large bodies of land. 94
Mass wasting Movement of rock, sediment, and soil
downslope due to the force of gravity. 381
Maximum humidity The maximum amount of wa-
ter vapor that a definable body of air can hold at a given
temperature. 143
Meandering stream A river or small stream that curves back
and forth across its valley. 422
Mechanical weathering The breakup of a body of rock into
smaller rocks of the same type. 373
Meridians Lines of longitude. 17
Meridional flow Jet stream pattern that develops when
strong Rossby waves exist and the polar front jet stream flows
parallel to the meridians in many places. 121
Mesa A broad horizontal surface, smaller than a plateau, that
is upheld by resistant caprock.

513

loess Windblown silt. 494
longitude The part of the Earth's grid system that deter-
mines location east and west of the Prime Meridian.

483

Strong updrafts that rotate within a supercell Mesocyclones

17 thunderstorm. 185