GLOSSARY - Physical Geography - page 153

Föhn wind The warm, dry wind that blows down the lee side (down-
side) of a mountain, causing the lee side of mountain ranges to be sig-
nificantly drier. The dryness occurs because water held by an air mass
will be released as it rises, cools and condenses over mountains to form
precipitation.
Food chain The feeding links between species within an ecosystem
indicating which species eat which other species.
Frost creep The downslope movement of the active layer. The soil
expands perpendicular to the sloping surface when it freezes, and settles
vertically on thawing, causing an overall movement downslope.
Gas hydrates Solid crystal structures in which the molecules of gas,
such as methane, are combined with molecules of water. Their appear-
ance resembles that of ice.
Gelifluction Creep of melted ground which is saturated by melt-
water above a permanently frozen layer. During the short seasonal
thaw in periglacial regions the upper soil layer is inundated with a
plentiful supply of water which helps cause the upper soil to slowly
move.
Genetic modification The scientific alteration of DNA, where genes
are deleted or added in order to change certain characteristics of a
species.
Geomorphology The study of landforms and their characteristics so that
their origin, development and history may be understood.
Geyser A hot spring that periodically jets water into the air.
Glacials Long, cold phases during the Quaternary (last 2.4 million years),
which saw the widespread advancement of glaciers and ice sheets.
Gleying The process by which a gley soil is produced. This happens
when iron and manganese compounds within the soil are subject to
stagnant, wet conditions and starved of oxygen so that the compounds
are 'reduced'. The result is a blue-grey soil.
Gondwanaland An ancient continent which was once made up of the
joined-up land masses of present day Australia, Antarctica, South
America and Africa.
Groyne A long wooden, concrete or stone barrier typically constructed
at right angles to a beach or river in order to trap sediment.
Gully A small valley eroded sharply into soil by running water.
Gyre A large, circular, rotating ocean current.
Hanging valleys A side valley to a main glacial valley that terminates at
a higher elevation than the floor of the main valley due to glacial
erosion in the main valley.
Herbivores An organism which consumes plant material only.