Sahel -a region in the centre of West Africa on the margins of the Sahara and prone to drought.

Salinisation -the deposition of salts at the surface of a soil in areas where evapotranspiration exceeds precipitation so drawing water up through the soil and with it salts that had been dissolved in it.

Saltation -the transport of load by bouncing along the bed of a river channel.

Salt marsh -an area of semi-vegetated tidal mudflat that becomes increasingly vegetated as sediments accumulate in sheltered waters allowing salt-tolerant plants to colonise them.

SALR -see saturated adiabatic lapse rate. 

Saline - of, containing, or concerned with salt (NaCl).     

Salinity -amount of salt in solution.      

Salt lake -inland body of water with a high salinity.

Salt pan -the dried out bed of a salt lake.

Sand -a particle of rock/mineral that has a diameter between 0.1 and 1.0mm.

Sand bar -a long strip of deposited sand lying offshore, usually only exposed at low tide, if at all.

Sand dune - a mound of sand deposited by wind in desert areas and along shore lines.

Sandur -see outwash plain.

Saprophyte -an organism which lives off other dead or dying organisms.

Satisficing -accepting what is satisfactory rather than chasing the maximum possible outcome.

Saturated -lit. full of water. No more can be held.

Saturated adiabatic lapse rate -the rate of fall in air temperature by adiabatic change as saturated air gains altitude. Varies between 4 and 9蚓 per 1000m. is slower than the DALR as latent heat is released during condensation.

Savanna -the biome found in tropical areas either side of the equatorial zone between 10˚ and 20˚.

Scale -in general use refers to the size of an area or time period. On maps, the scale indicates how many centimetres in the real world are represented by a centimetre on the map.

Scarp -the steep slope of an escarpment.

Scatter-graph -a graph which plots values by the use of dots. The dependent variable usually goes on the y-axis and the independent variable on the x-axis. The values are plotted as coordinates.

Scattering -the diffusion of insolation by particles in the atmosphere. This radiation does not reach the surface as a result.

Science park -an industrial estate near a university or other research establishment where it is hoped cooperation between business and research can lead to the commercialization of technological advances.

Schengen agreement -an agreement by some members of the EU to remove all travel restrictions for their nationals across the borders of the members.

Scouring -see abrasion.

Scree -highly angular rock pieces produced by freeze-thaw weathering and found at the base of a steep or vertical cliff face.

Sea breeze -a wind blowing from the sea to the land.

Sea-floor spreading - the widening of an ocean basin by the creation of new crust at a divergent margin.

Sea-level -average elevation of the surface of the oceans.

Sea-level change -two types:

• eustatic -a change in the volume of water held in the oceans as climate variations change the amount stored as snow and ice.

• isostatic -a change in the vertical position of the land due to the onloading or offloading of vast quantities of ice.

Seamount -an undersea volcano in a shield area.

Sea-wall -a steel and concrete wall built at the back of a beach, usually to protect a high value land area such as a town.

Sea-wave -at sea, waves represent a horizontal movement of energy but a vertical elliptical movement of water.

Secondary consumer - any animal which feeds on primary consumers or other secondary consumers.

Secondary forest -forest which is regrowing after the original vegetation was cleared.

Secondary sector - manufacturing industry.

Secondary succession -the process of revegetation of an area that has been cleared for some reason.

Second world -outdated term for the old communist bloc of the USSR and Eastern Europe.

Sectoral change -the general trend for the percentage of a workforce in agriculture to decline over time and for the secondary and then tertiary sectors to become increasingly important.

Sector model -based on 149 US cities, an urban land-use model which accounts for transport routes within the city. Suggests that industry and the wealthy make the first land-use decisions and the poor get whatever is left.

Sediment- any material, of any size, which has been eroded /weathered and then transported and deposited by water, wind or ice.

Sedimentary rock -any rock formed from sediments under pressure from other overlying sediments.

Sedimentation -the accumulation of sediment.

Sediment yield -total amount of sediment moved by a river over time, usually in m³/km²/yr.

Seed dispersal -movement of seeds away from parent plants.

Segregation -the location of particular groups of people into distinct areas separate from the general population, usually based on race, religion or economic circumstances.

Seif -a sand dune found in desert areas where the alignment is with the prevailing wind direction.

Seismic -lit. of an earthquake.

Self-employment -work as a freelancer or owner operator.

Self-sufficiency -the ability to survive without outside help.

Separatism -the efforts of certain groups to create autonomous regions, or even achieve national independence, for a particular area within an existing nation-state.

Sere -a particular type of plant succession.

Sesquioxide -the oxides of iron and aluminium that occur in soils.

Set-aside -the policy within the EU, begun in the late 1980s, in which farmers are paid for keeping land out of production. Introduced to address the overproduction of food in these countries.

Settlement -a location where people have built structures to use as a base for their existence.

Settlement morphology -the pattern and/or shape of a settlement.

Shanty town -an area of informal housing built by its residents on the edge of a city. The building materials are often waste from other sources and the land is occupied illegally. There are no services and all quality of life indicators are very low.

Share-cropping -a system of land rent where the farmer pays with a percentage of his yield rather than cash.

Shield area -ancient, stable area of crust away from plate margins and therefore unaffected by volcanic or earthquake activity.

Shield volcano -a volcanic cone made up of multiple layers of basaltic lava.

Shifting cultivation -a farming system in which a small tribal group cuts and burns the natural vegetation before cultivating the land. After a number of years the land becomes depleted and the group moves to a new area. The original land will recover after a period and the group usually rotates through three or four locations.

Shingle -the mixture of gravels, pebbles and shell fragments that accumulate on some beaches.

Shrub -a plant which has a thick woody stem but not thick or sturdy enough to be described as a trunk. Smaller than trees.

Sial -crustal material made mainly of silica and aluminium.

Silica (SiO₂) - most common mineral component of rock.

Sill -a sheet-like intrusion of magma between bedding planes.

Silt -a particle of rock/mineral with a diameter between 0.01 and 0.1mm.

Silurian -a period of geologic time lasting from 438m to 408m years ago.

Sima - crustal material made mainly of silica and magnesium.

Sinkhole -see swallow hole.

Sinuosity -the endiness-of a river course i.e. how far removed it is from a truly straight line course.

Site - the point at which a settlement is located.

Site factors -those characteristics of a site which make it suitable for settlement. 

Site of Special Scientific Interest -sites having special and unique natural characteristics which are deemed worthy of legal protection.

Situation -the relationship of a settlement site to its surroundings and thus a factor in whether the settlement will grow or not. 

Slash and burn -another term for shifting cultivation.

Sleet - a form of precipitation where snow falls through warmer air and arrives at the surface partially melted.

Slip-face -the lee side of a sand dune so called because material often slides or rolls down it.

Slum - an area of old, rundown housing where living and social conditions are very poor.

Slump - see rotational movement.

Smelting – processing of metal ore in order to extract the metal in its pure form. The word is probably from the Middle German for “melt” and heat is indeed the main requirement but other chemicals (called fluxes) are required as catalysts and to deal with various types of impurities. The exact temperatures and chemicals required will depend on the metal being extracted, the ore in which it is held, and the nature of the ground from which it was taken.

Smog -a mixture of smoke and fog produced by factory and domestic emissions which provide hygroscopic nuclei for condensation to occur onto.

Snout - the front end of a corrie glacier or valley glacier.

Social elite -the wealthiest section of society.

Snow line -two types:

• the division between the zone of accumulation and the zone of ablation on a glacier.

• the elevation at which there is a division between snow covered and uncovered ground.

Snow melt -the spring and summer mass thawing of snow and ice which provides a sudden and massive increase in discharge to downslope rivers.

Social provision -the basic needs that a society should provide or aspire to provide for its members such as housing, healthcare, education and the like.

Soft-engineering - solutions to problems of resource management involving working with nature (adaptation).

Soil - the very upper layer of the land surface made up of mixture of regolith, decomposed organic matter, air and water.

Soil conservation -the protection of a soil from erosion plus the maintenance of its fertility so that its productivity is maintained.

Soil creep -slow mass movement of soil downslope due to outward expansions brought on by water infiltration which lead to downward movements under gravity as water moves out of the soil.

Soil fertility -the ability of a soil to provide nutrients for plant growth.

Soil profile -the variation in soil characteristics through its depth.

Soil structure -the pattern of aggregated soil particles into certain shapes of peds.

Soil texture -the ratio of sand, silt and clay within a soil.

Solar constant -the amount of energy received per unit area from the sun over a given period of time.

Solar radiation -see insolation.

Solfatara -a minor extrusive volcanic feature where gases escape from surface cracks and vents.

Solifluction -a mass movement of soil in periglacial areas when upper layers thaw in summer and are lubricated in comparison to the permafrost below.

Solute - material dissolved in water.

Solution -the taking of minerals into water and removing them through flow.

Solution load -that portion of a river load held in solution.

Source - the start point of a stream or river.

Source region -the type of area from which an air mass originates. 

Sovkhoz -see collective farm.

Spearman Rank Correlation Coefficient -a statistical measure of the degree to which two sets of data are correlated according to the formula:

                R_s = 1 -6x ∑d²

                                   n³ -n

            where d is the difference between the rank values of the data sets. While it can show how strongly data is correlated it is not a measure of cause and effect.

Specialization -at different scales, the concentration of effort into particular areas so that the efficiency and quality are maximized.

Sphere of influence -the area surrounding a settlement which is influenced by it in economic, political and social terms.

Spheroidal weathering -the chemical weathering of blocks of rock so that they take on a more rounded shape.

Spit - an embankment of sand which juts out from the land, often across a river mouth. The unattached end is usually curved in towards the land. Sediments may accumulate behind the spit to form salt marsh and eventually reclaimed land.

Sporadic permafrost -where mean annual temperature is just below 0˚

there may be isolated patches of frozen ground.

Spread effect -the transfer of resources away from a core area to a peripheral area due to diseconomies of scale.

Spring - the emergence of water from the ground, usually leading to the formation of a channel flow.

Spring-line -a line of springs emerging from a valley side at approximately the same height which reflect the underlying rock conditions.

Spring tide -extremely high and low tides which occur twice a month when the sun and moon align on the same side of the earth and exert a combined gravitational pull on the oceans.

Squall line: A line of severe thunderstorms that can form along and/or ahead of a cold front.

SSSI - see Site of Special Scientific Interest.

Stability -when the DALR and SALR are both higher than the ELR then an air mass will be cooler than its surroundings and will sink back to its original position once the upward forces on it have ceased e.g. getting over a mountain range.

Stack - a pinnacle of rock standing just off a headland and formed when an arch collapses.

Stadial -a short-term advance of ice during a more general interglacial period.

Stalactite -a spindly deposit of calcium carbonate found hanging from the ceilings of caves in limestone areas. Water dripping from the ceiling releases carbon dioxide (reverse of carbonation) allowing the calcium carbonate to precipitate.

Stalagmite -a similar feature to a stalactite, formed by the same process, but found on the cave floor beneath the stalactite above. Tend to be shorter and more rounded due to the impact of the falling drip. 

Staple food crop -the main crop which forms the basis of calorific content of the diet for a particular area. Usually a carbohydrate food such as cereals or tubers.

State industry -one which is owned and operated by the government.

Stemflow -the flow of water down stems and trunks after interception of rainfall.

Steppe - the temperate grasslands of Eurasia which stretch from Hungary to Mongolia.

Stevenson screen -a white, usually wooden, box with louvre sides and raised on stilts used to hold thermometers at weather recording stations.

Stewardship -an approach to environmental management which advocates careful balance between development and protection of the environment.

Stilling well -a tube of wide diameter sunk into a river bank which thus allows an accurate and constant measurement of the still water surface level of the river itself.

Stokes- Law -the settling rate of a particle in water is proportional to the diameter of that particle i.e. larger particles settle quicker.

Stone circle -a circle of large stones found in periglacial areas when the formation of an ice lens just beneath the surface creates a dome from which stones on the surface roll away.

Stone lines - Stone lines are long rows of stones piled together to form barriers across your field. They do not store water. They do something else that is important if you want to prevent erosion. The stone lines slow the flow of water across your fields. They work on both flat and sloping land. The stone lines force the water to spread over the soil so that it can be absorbed into the soil instead of running off the field.

Storm beach -the highest part of a beach, created by a strong storm, which rests above the usual high water mark.

Storm surge -the pushing of water against a coastline to abnormally high levels, usually a combination of extreme low pressure and winds pushing water into a narrowing feature such as a bay or estuary.

Stoss - the exposed side of a slope.

Strata - layers of deposited material.

Stratosphere -layer of the atmosphere from approximately 12 to 50km. found above the tropopause. Temperature increases with height due to absorption of solar energy.

Stratus cloud -a layered cloud found below 2.5 km which produces light drizzle.

Stream order -classification of streams within a drainage basin so that it can be compared with another. Different methods have been proposed with Strahler being most common. From a source to a confluence, a stream is considered 1^st order. When two 1^st order steams join, the resultant stream is a 2^nd order stream. Where two 2^nd order streams join a 3^rd is created and so on. When streams of different orders join, the resultant stream remains as the higher order of the two that came together.

Striations -scratch marks or grooves found on a rock surface that has experienced glacial abrasion.

Strip farming -the splitting of a larger field into smaller strips which are looked after by individual farmers.

Sub-aerial processes -all physical processes occurring at the surface.

Subduction -the movement of an oceanic plate beneath another crustal plate. The plane of contact is known as the Benioff Zone where earthquakes occur. As the plate reaches the asthenosphere it melts.

Sub-glacial -lit. under the glacier.

Sublimation -transformation between solid and gas, and vice versa, without being in a liquid stage.

Submergent plants -see aquatic plants.

Submergent features -those formed where a coastline experiences a relative rise in sea-level.

Subsequent stream -a tributary created by headward erosion.

Subsidence -sinking to a lower level.

Subsidy -a government grant used to save or stimulate a particular operation or whole industry sector.

Subsistence -farming system where the farmer produces just enough to sustain himself and his family.

Succession -the development of a plant community over time.

Succulent -a plant that has adapted to drought conditions by being able to store water in its stem or leaves.

Superimposed drainage -a drainage pattern that formed on one set of rocks which have since been removed and so bears no relation to the set of rocks on which it is now found.

Supra-glacial -on the surface of a glacier.

Suspension -the transport of load in the body of the water in a river i.e being carried along in the flow.

Sustainable agriculture -the increase in food yields without damage to the environment.

Sustainable development -development strategies that do not compromise the ability of future generations to meet their needs.

Sustainable resources -those resources which can be managed to provide an ongoing yield. Exploitation must not exceed renewal rates or they cease to be sustainable.

Swallow hole -the point at which a river channel may disappear underground. Usually found on limestone where joints may come to the surface and provide a conduit into which the river can disappear.

Swamp -an area, usually vegetated, permanently flooded or at least saturated by groundwater.

Swash - the running of water up a beach under the momentum of a breaking wave.

S-wave - a seismic wave which moves material in a motion perpendicular to the direction in which the energy of the wave itself is travelling.

Swell - see sea-wave.

Synoptic chart -a weather map.

System - any set of components which are gathered into a working whole.

Systems theory - A theory designed to understand whole systems, including socio-ecological systems. In a system, levels are linked in interdependent and interacting ways.