GLOSSARY - Physical Geography - page 155

food chain, which if lost could result in collapse of the food web and
major loss of biodiversity.
Lapse rate

The rate at which air temperature decreases with increasing

altitude.
Laterisation Warm weather and plentiful rainfall result in fast weather-
ing conditions and leaching of material within soils. Laterite soils are
produced which are often orange or red in colour. These soils often
have little organic matter since decomposition and leaching removes
this material quickly.
Leaching The removal of dissolved soil material vertically through the
soil profile by surplus water.
Litter Soil organic matter consisting of decomposing plant and animal
debris.
Longshore drift The transport of sediment along the coast by longshore
currents which surge towards the beach at an oblique angle, followed by a
backwash that transports sediment at right angles to the coast, resulting in a
zigzag movement of material along the coast.
Macropore flow The transfer of water through the soil between large
pores greater than 0.1 millimetres in diameter.
Marl Loose, earthy deposit with high concentrations of limestone.
Massive ice Isolated bands or lenses of ice several metres thick within

soils.
Matrix flow The transfer of water through the soil between micro-
scopic pores smaller than 0.1 millimetres in diameter.
Meander A bend in a river channel.
Metamorphic rock Rock which has been subject to heat and pressure
which has resulted in a change to its structure or composition.
Mineralisation The release of plant nutrients during decomposition of
organic matter, which can then be used by other organisms.
Moraines Linear mounds of glacial till that have been transported by a
glacier. They are classified according to the method of their
deposition.
Mud pot A small, hot spring consisting of bubbling mud.
Natural greenhouse effect Atmospheric greenhouse gases, such as
carbon dioxide and water vapour, absorb 90 per cent of the long-wave
radiation emitted from Earth, resulting in an average global tempera-
ture approximately 35°C warmer than would be experienced without
the natural levels of greenhouse gases present.
Neap tides When the Sun opposes the gravitational pull of the Moon
on the Earth (i.e. the Earth is positioned between the Sun and the
Moon) the tidal range is reduced, resulting in lower high tides and