Glossary - Fundamentals of the Physical Environment - page 746

Resilience Degree of an ecosystem's or a population's
stability that is measured by its speed of recovery after
suffering a disturbance.
Resistance The sum of forces in Earth materials
mobilized to resist shearing or other forces.
Resistant residue Soil minerals relatively resistant to
weathering which therefore tend to accumulate in soils
(e.g. heavy minerals, quartz, feldspars).
Resorption The process of crustal recycling whereby
oceanic and other material is partially or completely
melted in the higher temperatures and pressures of a
subduction zone.
Respiration The breakdown of organic compounds,
using oxygen to obtain energy for metabolic processes.
Reverse weathering A reversal of sea-floor chemical
weathering which precipitates solid phases of minerals
previously taken into solution; includes the important
biochemical precipitation of calcium carbonate and silica.
Reynolds number A value which distinguishes between
laminar and turbulent stream flow, dependent on the
relative values of hydraulic radius , water velocity and
viscosity.
Rheologic property The ability of an essentially solid
material to deform and flow under stress.
Rhourd

Rock cycle The global geological cycling of lithospheric
and crustal rocks from their igneous origins through all
or any stages of alteration, deformation, resorption and
reformation.
Rock debris The initial angular fragments produced by
weathering of a rock face.
Rock flour Fine debris produced by subglacial abrasion
and usually flushed out as suspended sediment in
meltwater.
Rock glacier A slow-moving mass of angular rock debris
with sufficient interstitial or subjacent ice for it to flow like
a glacier, usually found in arid cold climates.
Rock platform A wave-cut platform across a rock surface
in the intertidal zone.
Rock weathering See weathering .
Rockfall A free fall of rock debris .
Rotor A small, overturning turbulent eddy in the air
stream downwind of a mountain range; it may generate
a rotor cloud if the rising and falling limbs pass through
a condensation level.
Rubefaction Reddening of soils caused by the release of
iron oxides in chemical weathering.
Sabkha A salt-encrusted plain marked by the accumu-
lation of evaporite rocks, usually on tidal flats ; also used
to describe an inland salt pan or playa .
Salina A general term used for a surface depression of
periodic flooding and evaporation which leads to the
accumulation of evaporite rocks.
Salinity The mass of total dissolved salts present in sea
water, measured in g kg -1 (‰).
Salt efflorescence A precipitation and growth of salt
crystals from a fluid in rock or soil voids.
Salt marsh A halophytic plant community occupying
intertidal mudflats, exhibiting a weak progression in
diversity and productivity shorewards as the frequency of
tidal inundation falls; its surface is flooded and drained
through a series of tidal creeks.
Salt weathering The granular disintegration of rock
caused by salt efflorescence which acts as an important
mechanical weathering agent through its generation of
high tensile stress.
Saltation The movement of sediment particles by
turbulent entrainment in water, wind or by grain ballistics ,
followed by short jumps or bounces along the bed.
Sand wave A large wave- or dune-like sand bed form
formed by fluid motion normal to its axis.
Sandur An outwash plain forming the superficial land
surface in piedmont or coastal zones beyond glacier
margins.
Saprolite

A pyramid sand dune formed in a variable wind

field.
Ria A marine inlet formed by the flooding of a coastal
river valley by eustatic rise in sea level or isostatic
depression.
Ridge push A component of sea-floor spreading driven
by gravity-sliding away from the elevated mid-ocean ridge .
Riegel An abraded, cross-valley rock barrier in a

glaciated valley.
Riffle A stream bed accumulation of coarse alluvium
linked with the scour of an upstream pool .
Rift valley A valley formed by crustal downfaulting,
normally between two parallel faults; it gives a topo-
graphic expression to a graben.
Rill The smallest and most transient of stream channels,
eroded during intermittent surface flow and liable to
collapse or infill between precipitation events.
Rip current A narrow and intermittent current, fed by
longshore currents and draining seaward through the
nearshore zone , where it may be vigorous enough to cut a
rip channel in the sea bed.
Rising limb The component of a hydrograph which
marks the increase in stream discharge during the time of
rise to the peak discharge , in response to a precipitation
event.
Roche moutonnée A valley-floor glaciated bedrock
hump with a streamlined, abraded uphill face inclined
gently up-valley and a steep, quarried downhill face.

A soft in situ residue of chemically

decomposed rock.