some terms of Geography

Sahel Sahel refers to a narrow east-west zone of semi­desert in North Africa along the southern fringes of the Sahara. In its modern use, it refers to a vegetation zone in which the Savanna grasslands phase into desert.

St. Elmo's Fire Named after a fourth century Italian saint, St. Elmo's fire refers to an electrical discharge of blue­green colour which occurs when there is a strong electrical field in the atmosphere. Such a discharge manifests itself during thundry weather on protuber­ances such as aircraft wing tips and weather vanes.

Saline Soils Saline-soils are intra-zonal soils containing high proportion of soluble salts such as sodium chloride (common salt). They often occur in semi-arid and arid areas where there is strong evaporation.

Sandstone Sandstone is a type of sedimentary rock. It consists primarily of grains of quartz (major constitu­ent), mica, feldspar and other minerals. It has rounded sand particles.

Sandstorm Sandstorm is a storm in desert or semi-arid area when strong winds lift and transport relatively large grains of sand. It differs from dust storm, in that, the sand particles do not rise more than a few metres above the gr.ound.

Sandur Sandur is an Icelandic term for an outwash plain.

Santa Ana (Anna) A Spanish term for the fohn-type wind, Santa Anna blows south-westwards as a hot air in the USA. It occurs mainly in winter. If it occurs in spring, it causes severe damage to fruit trees Savanna (Savannah, Savana) Sayanna refers to tropical grasslands. The savanna vegetation zone, midway be­tween the deserts and the tropical rain forests, com­prises scattered bushes and trees and various heights of grass. The trees are not forest trees but thorny xerophytes with reduced leaves. Savanna is known as llanos in Venezuela and Columbia and the Campos in Brazil.

Schist Schist is a well-foliated, medium-to"coarse grained rock created by the effects Qf"regional' metamorphism. The major minerals of which the schist is composed have a flaky or fibrous appearance.

Sea mount A sea mount is an isolated mountain rising abruptly some 1,000 metre from the ocean floor, but without extending above sea-level. It is probably of volcanic origin. Sea mounts occur most frequently in the Pacific Ocean.

SedimentJhe term sediment refers to particles transported and deposited by a fluid. Sediments are most commonly composed of rock particles.

Sedimentary Rock A rock composed of sediments and generally having a layered or stratified appearance is called sedimentary rock. Sediments are largely derived from pre-existing rocks. Sandstone, shale, etc., are examples of sedimentary rocks.
Seismology Seismology is the scientific study of earth­ quakes, their ca~s, effects and distribution.

Selva A Portuguese term, selva refers to the equatorial rain forest of the Amazon basin in South America. The term is now also used to describe similar types of vegetation elsewhere in the world.

Sequential Landforms The landforms formed by modifi­cation of .the initial landform are called sequenJ
landforms.

Serir An Arabic term, serir refers to a desert area cover~ with gravel and cobbles in Libya and Egypt in norB east Africa. It is equivalent to the reg of north-w~ Africa (Algeria).

Sextant Sextant is an instrument for me ring the anguli distance between two points or objects, chiefly ( celestial bodies. It is widely used in marine navigatiOl
Shale Shale is well-laminated argillaceous sedimentary r~ consisting of layers of clay and silt particles. It is a fissil rock, i.e., it splits easily along its bedding planes in thin flakes of rock.

Sheet Erosion (Sheet Wash) Sheet erosion refers to t~ wide spread removal of surface debris, i.e., soil overland flow on low-gradient slopes. It comprises, two processes: raindrop impact and overland flow. sheet erosion, sheets wash away the particles dislodgec by the falling rain.

Shield A shield is a large, extensive and rigid block of th~ earth's crust that has been unaffected by mountain building for a lengthy period of geological time. Shield] are composed of Pre-Cambrian rocks, the oldest rocle on the earth's surface. The Laurential Shield (Norti America) and Baltic Shield (Europe) are typical example~ of shields.

Shingle A deposit of coarse gravel or pebbles, especiall} on a beach, is known as shingle. Coarse shingle ridges, known as storm beaches, are formed at the upper limil of the beach by storm waves.

Sial and Sima Sial are the relatively light rocks that fOrIn the earth's crust. Such rocks are composed predomi­nantly of silica (Si) and aluminium (AI). Hence the name sial. Sial has lower density than sima.

Sima refers to that part of the earth's crust which is composed of mineral rich in silica (Si) and magnesium (Mg). It is covered by sial in some places. It comprises most of the ocean floor. Hence its alternative title is oceanic crust.

Sidereal Day The time interval equivalent to one complete rotation of the earth in relation to the stars is called
sidereal day. Its length is 23 hours 56 minutes 4.091 second, i.e., a sidereal day is almost 4 minutes shorter I than a mean solar day.

Sidereal Year The time interval during which the earth: makes one complete revolution around the sun with reference to the stars is called a sidereal year. It is equal' to 365 days 6 hours 9 minutes 9.54 second.

Silica Chemically, silica is silicon dioxide (Si02). It is most I abundant of all minerals in the earth's crust. It occurs in different forms (polymorphs). Quartz, trydymite and cristobalite are the three main forms. Other forms include chalcedony and opal Silt Silt is one of the finest of the clastic sediments. It is coarser than clay but finer than sand.

Sirocco (Scirocco) Sirocco is a very hot, dust-Iaddt!n, south or south-easterly wind blowing from North Africa­across the Mediterranean sea to Sicily and South Italy. Although it starts as a dry wind, it picks up moisture­as it crosses the North African coast and by the time it reaches Sicily and Italy, it has become humid, oppres­sive wind.

Slate Slate is a fine-grained rock produced from argillaceous rocks by metamorphism. It is characterised by a well­developed cleavage along which it splits quite easily.
Small Circle Small circle refers to a circle on the earth's surface whose plane does not pass through the centre of the earth. All parallel of latitude except the equator are small circles.

Smog (Smoke Fog) Smog is a form of fog that occurs in areas where the air contains a large amount of smoke. The smoke gives the fog an acrid taste .because of the chemicals, especially sulphurdioxide. Smog is synomous with photo-chemical fog.
Snow Line The lower limit of snow cover in a landscape is called snow line. Snow line is also defined as the line below which snow melts away in summer. It varies in altitude according to latitude and degree of continentality. It is higher in the regi011Jl.way from ocean and in the tropics. It is lowest near the poles.
Soil Soil is defined as the surface material composed of mineral particles and humus, water and air in which plants grow. It covers much of the earth.

Soil Profile Soil profile refers to a vertical section of soil in which all the soil horizons, from the ground surface down to the parent material, are shown.
Solar Constant The term solar constant denotes the inten­sity of solar radiation received on a unit area of the horizontal surface at the outer limit of the atmosphere.

Solar Day The time intervaf between the two successive transits of the sun across a given meridian is' called solar day. The mean solar day is 24 hours. The solar day varies slightly with latitude as the earth's orbit is ellipsoid and inclines towards the equator.

Solarimeter (Radiometer) Solarimeter is an instrument which measures the intensity of solar radiation received at the earth's surface. The instrument is based on the principle that the temperature of body rises when it absorbs radiation.

Solstice Solstice is defined as one of the two dates in a year on which the sun reaches its greatest altitude north and south of the equator. The sun is directly overhead along one of the tropics on these dates. The summer solstice for Northern Hemisphere is about 21st June, while the winter solstice for Northern Hemispher~ is 22nd Decem­ber. The summer solstice has the year's longest day, while the winter solstice has the shortest.

Sorghum Sorghum is a tropical grass. It has a number of varieties.

Southern Oscillation (Walker Circulation) Southern Oscil­lation refers to a perturbation in the inter-tropical general circulation, especially in the Indian Ocean and the southern Pacific. According to G. Walker, who introduced this term, when pressure over the Pacific is high, it tends to be low over the Indian Ocean. This phenomenon has important consequences on precipita" tion amount.

Spit A long deposit of sand or shingle or both extending out into the sea is termed spit. Spits are formed by long­shore drift of material. They may form at headlands between bays.

Spring In climatology, spring is the name given to the season between winter and summer. In geomorphol­ogy, the term spring refers to natural flow of water from the ground at the point where the water table inter sects the surface.

Spurs Spurs are the ridges which project downwards from the crests of mountains as water partings. They are mainly classified into two categories: interlocking spur and truncated spur. Interlocking spur is the spur pro­jecting from one side of a V-shaped valley that inter­locks between two corresponding ridges on the oppo­site side of the valley. A truncated spur is the spur whose end has been carved off through erosion by a glacier that formerly occupied the valley.

Squall Squall is the short-lived strong wind which arises suddenly. It is most commonly associated with a front or an area of convection. Hence, it is often accompanied by rain.

Stalactite and Stalagmite A stalactite is a candle-like growth of mineral matter hanging from the roof of a limestone cave. Stalactites are formed when water running through the cave above and containing dissolved minerals (es­pecially calcium carbonate) evaporates and deposits the minerals. They are normally accompanied by stalag­mites which are mineral columns on the floor of a limestone cave. Stalagmites are formed when calcium carbonate deposited as drips from the stalactites evapo­rate on the floor. They are generally shorter and fatter than stalactites.

Standard Time Standard time is mean time of a meridian (located more or less centrally over a country), which is adopted as the time system for the whole of a
country. It is different from local time based on sun's position.

Stefan's Law Stefan's Law relates to the intensity of solar radiation received at the earth's surface and the amount of terristerial radiation (the energy re-radiated by the earth). It is based on the assumption that both the sun and the earth behave as black bodies.

Steppe A Russian term, steppe refers to the mid-latitude grasslands which extend from Central Europe to Siberia through Eastern Europe and Central Asia. Steppe grass­land is generally drier than the North American prairies.

Strait A strait is the relatively narrow waterway that links two large bodies of water.

Stratification In biogeography, the term stratification refers to the layered arrangement of vegetation. In geology, it refers to the accumulation and division of sedimentary rocks into horizontal layers or beds known as strata.

Stratigraphy Stratigraphy, also called historical geology, is the branch of geology which deals with the composition, sequence, distribution, classification and correlation of the stratified rocks.

Stratocumulus Stratocumulus is the term used to describe a sheet or layer cloud, which is grey and whitish in - colour and visible within the general layer. This type . of cloud extends from about 500 m to 2,000 m.

Stratosphere Stratosphere is a layer of the atmosphere. It occurs between the troposphere (below) and the me­ sosphere (above). It extends from sa km above the