GLOSSARY - Physical Geography - page 159

Shore platforms A flat or gently sloping wave-cut platform found at
the base of a rocky cliff cut into the rock.
Soil horizons Layers of soil within a soil profile, distinctive in terms of
colour and texture, created by the leaching and deposition of soil
materials caused by water moving vertically through the profile.
Solifluction The slow movement of soil material downslope, where a
saturated thawed layer moves across a layer of permafrost under
gravity.
Solute flux The total movement of dissolved material through a system
as measured by mass (e.g. kilograms).
Speciation The evolution of a new species, whereby small changes in
the characteristics of successive generations leads to a species that is dif-
ferent from the ancestor from which it originated.
Spit A narrow strip of sand that protrudes into the sea, usually curved in
a seaward direction, with one end attached to the mainland. Spits occur
where the shore direction changes, e.g. at the mouth of an estuary.
Spring tides A tide that occurs on or around the time of a new or full
Moon, which is characterised by unusually high or low tides. It occurs
when the Sun and Moon are in alignment, reinforcing the gravitational
pull of the Moon on the Earth.
Stack A steep column of rock protruding above the sea.
Stoss-and-lee forms Smoothed rock outcrops formed by basal sliding
of a glacier, streamlined in the direction of glacier flow, with a plucked
steep side facing downstream and a tapered end facing upstream.
Striations Small erosional features, with an appearance similar to
scratches, caused by basal sliding of a glacier with embedded particles at
the base of the ice, flowing over a rock surface and creating grooves.
Subduction zone Subduction can occur where two oceanic plates
are forced together and one slides beneath the other, or where
an oceanic plate is forced beneath the less dense continental plate.
The plate material is then melted by the mantle beneath the Earth's
crust.
Sublimation The process by which a solid changes directly into a gas.
Succession The changes to the structure and make-up of an ecological
community over time.
Surf zone The area where the water depth becomes too shallow for
waves, causing them to break.
Tarn A small lake that occupies the basin of a cirque.
Temperature inversion Air temperature increases with altitude,
usually where a layer of warmer air overrides a layer of cooler air. The
reverse of the normal environmental lapse rate.