Glossary - Discovering Physical Geography - page 576

Fjord A former glaciated valley along the coast that is
flooded by rising sea level. 508
Flood stage The level at which stream discharge begins to
spill out of the channel into the surrounding area. 418
Foredune A dune that forms parallel to the shore when sand
blows inland from the beach. 521
Foreshore The nearshore zone that is regularly exposed and
submerged through the tidal fluctuations and movement of
surf. 519
Fossil fuels Carbon-based energy sources, such as gasoline
and coal, that are derived from ancient organisms. 227
Freezing The process through which water changes from the
liquid to solid phase. 139
Frontal uplift Uplift of air that occurs along the boundary of
contrasting bodies of air. 157
Frost heaving Upthrust of sediment or soil due to the freez-
ing of wet soil beneath. 374
Frost wedging Expansion and contraction of water in rock
cracks due to freezing and thawing. 373
Fumerole A steam vent that results because underlying
groundwater is boiled away before reaching the
surface.

Glacial plucking An erosional process by which rocks are
pulled out of the ground by a glacier. 457

Scratches in rock produced by glacial

Glacial striations

abrasion. 457

Sediment deposited directly by a glacier. 461

Glacial till

Glacial trough

A deep, U-shaped valley carved by an alpine

glacier. 460
Glacier A slow-moving mass of dense ice that flows under
its own weight. 448
Graben A downthrown block of rock that lies between two
steeply inclined fault blocks. 352
Graded stream An idealized stream that has achieved
a balance between sediment transport and stream
capacity. 423
Great circles Circles that pass through the center of the
Earth and that divide the planet into equal halves. 14
Greenhouse effect The process through which the lower
part of the atmosphere is warmed because longwave radiation
from Earth is trapped by carbon dioxide (CO2) and other
greenhouse gases. 64
Groin A short, low wall built at a right angle to the coast that
intercepts the longshore current. 531
Ground ice Distinct zones of frozen water that occur in
permafrost regions. 475
Gulf A relatively small body of salt water that is surrounded
by land on three sides and opens to a sea or ocean. 506
Gyres Large oceanic circulatory systems that form because
currents are deflected by landmasses.

368

G
Gelisols Soils in subarctic and arctic environments that
contain permafrost within 2 m of the surface. 291
Geologic time The period of time that encompasses all of
Earth history, from its formation to the present. 322
Geomorphology The branch of physical geography
that investigates the form and evolution of the Earth's
surface. 342
Geostationary orbit An orbit where satellites remain over
the same place on Earth every day. This orbit is achieved
because the satellite is placed very high above Earth and
travels at the same speed as the Earth's rotation. 34
Geostrophic winds Airflow that moves parallel to isobars
because of the combined effect of the pressure gradient force
and Coriolis force. 114
Geyser A superheated fountain of water that suddenly sprays
into the air on a periodic basis. 367
Glacial abrasion An erosional process caused by the
grinding action of a glacier on rock. 457
Glacial drift Sediment deposited indirectly or directly by a
glacier. 461
Glacial erratics Large boulders that have been plucked and
transported a great distance before they are deposited.

132

H
Hadley cell Large-scale convection loop in the tropical
latitudes that connects the Intertropical Convergence Zone
(ITCZ) and the Subtropical High (STH). 118
Hanging valley An elevated U-shaped valley (with respect to
a glacial trough) formed by a tributary alpine glacier. 460
Headland A portion of the coast that extends outward into a
large body of water. 515
Heterotrophs Organisms that consume complex organic
substances for food. 236
High-pressure ridge An elongated area of elevated air
pressure in the upper atmosphere that is typically associated
with sunny skies and calm winds. 176
High-pressure system A rotating column of air
that descends toward the surface of Earth where it
diverges. 108
High latitudes The zone of latitude that lies from about 55˚
to 90˚ in both hemispheres. 17
Histosols Organic soils that form in cool, wet environments
where organic carbon decomposes very slowly.

457

Deep furrows in rock produced by glacial Glacial grooves

abrasion. 457
Glacial outwash Sediment deposited by meltwater streams
emanating from a glacier.

463 291