Glossary - Fundamentals of the Physical Environment - page 895

Laterite A reddish tropical clay composed of the sesquioxides of iron and aluminium,
and kaolinite ;it hardens irreversibly on drying, often with a concretionary structure.
Lava An extrusive flow of molten magma and the rock into which it solidifies.
Law of the minimum The law which states that the productivity of an ecosystem is
controlled by, or is proportional to, the growth factor which is operating at a minimum
(i.e. in shortest supply).
Leaching The washing out of materials in solution or suspension from a soil horizon or
profile.
Leading edge The advancing edge of a continental plate, marked by a coastal orogen,
narrow continental shelf and deep offshore trench which influence the nature of
coastline development (cf. trailing edge ).
Leaf area index A measure of the density of vegetation surfaces capable of intercepting
precipitation, given as the total area of leaves in the layered canopy covering a unit
area of ground.
Leaf drip The concentration and onward transfer, as large drops, of precipitation
intercepted by a leaf.
Leaf leaching The removal by rainfall of chemicals, including nutrients, from the surface
and interior of a plant leaf.
Leaf uptake The uptake of nutrients via stomata on leaves.
Lee wave A lens-shaped cloud forming in a standing wave of turbulent air in the lee of a
mountain barrier, with continuous condensation as air rises and cools at its leading
edge and evaporation as air falls and warms at its trailing edge.
Levée A bank of coarse debris flanking a floodplain river, formed by the concentration of
suspended sediment during overbank discharge ; boulder levées also flank debris flows
as a result of collision and ejection during their turbulent flow.
Limiting equilibrium A state of balance between shear stress and shear strength - or
eroding and resisting forces - in Earth materials, defined by Mohr-Coulomb criteria .
Lineament A large-scale, linear feature of tectonic or other structural origin, visible at
the land surface; it may be (or represent the trace of) a fault , suture , fracture zone, etc.
Liquid limit The critical water content of a granular solid beyond which it develops
liquid behaviour.
Lithification The transformation of unconsolidated sediments into a cohesive rock mass
through syngenetic and diagenetic dewatering and cementation, compaction and
crystallization.
Lithology The macroscopic character of rock mass determined by its geochemical
(mineral) and mechanical (particulate) components and related structures.
Lithosere The sequence of plant communities which, successively, occupy a bare rock
surface.
Lithosphere The rigid, outermost solid layer of Earth and its upper mantle, which
supports crustal plates .
Little Ice Age The period from about AD 1500 to AD 1800 when climatic conditions in
Europe were much colder than before or since. Many glaciers advanced in the Alps
and Scandinavia.
Load The total mass of mineral and organic sediment transported by a stream by bed
traction, suspension and solution.