GLOSSARY - Physical Geography - page 158

Rock glaciers A tongue-shaped body of rock and angular sediment
that flows very slowly downslope like a glacier. Ice often occurs within
pore spaces between the rock particles, which aids movement.
Rossby waves Large upper-atmosphere undulations which disturb the
belt of prevailing westerly winds associated with the Ferrel cell. They
contain jet streams.
Safety factor (also known as factor of safety) The ratio of the forces
resisting movement to the forces promoting movement of material
downslope. If the value is below 1, movement will occur.
Salinisation The collection of soluble salts within a soil that can have a
detrimental impact on soil fertility. It concerns salts of sodium, magne-
sium and calcium.
Salinity The concentration of salt dissolved in water.
Saltating A method of sediment transport whereby sediment grains are
bounced along a bed surface.
Saturated adiabatic lapse rate See dry adiabatic lapse rate for explana-
tion of 'adiabatic'. The saturated adiabatic lapse rate is applied to air
parcels that have reached dew point, which causes water vapour within
the air parcel to condense into liquid water. This process releases heat
and warms the air parcel, meaning the saturated adiabatic lapse rate is
less than the dry adiabatic lapse rate. The saturated adiabatic lapse rate
varies according to the temperature and moisture content of the air.
Saturation-excess overland flow Where all of the pore spaces within
the soil become filled with water, and therefore saturated, forcing the
excess water to flow across the surface.
Savanna A grassland environment, with a low density of trees, which is
hot with an annual dry season.
Sedimentary rock Rock which had developed as sediment has accu-
mulated over time and then become compressed and slowly formed solid
matter.
Segregated ice A lens of ice found just below the active layer, which
grows because of migration of water from around the lens to the freez-
ing point.
Sesquioxides Contain three oxygen atoms and two atoms (radicals)
from a different substance.
Shear stress A stress acting upon a particle in the same direction as the
surface it is resting upon. In rivers the shear stress is the velocity of
flowing water. When a sediment particle can be lifted from the river
bed then the critical flow velocity (critical shear stress) is reached.
Shoaling A gradual decrease in water depth that causes waves to
become higher as they move towards the land.