Hadley Cell The Hadley cell is one of the parts of the global atmospheric circulation pattern of winds. This part or cell extends from the equator to about latitudes 30° N and S. In it, air, rises at the intertropical convergence zone (ITCZ) near the equator before flowing polewards at high altitudes. The cell is named after its inventor G. Hadley.

Hail Precipitation in the form of pellets of ice that develop in and fall from a cumulo-nimbus cloud is called hail. Hail is associated either with the passage of a cold front in temperate latitudes or with rapidly ascending convec­tion currents in low latitudes.

Hamada (Hammada) An Arabic term, hamada or hammada refers to an extensive flat rocky surface in desert from which sand has been removed by the wind. Hamadas are very frequent in the Sahara and Gobi deserts.

Hanging Valley A hanging valley is a tributary valley that lies above the main valley and is separated from it by a steep slope. A river flowing down the hanging valley descends to the main valley as a waterfall or series of rapids. Hanging valleys are more common in glaciated areas.

Hawaiian ‘High’ Located in Northern Pacific, the Hawaiian ‘high’ is one of the high-pressure cells in the atmospheric circulation. Such a cell is more pronounced in the northern summer than in the northern winter.

Haze The term haze refers to an obscurity of the lower atmosphere that limits visibility to under 2 km but over 1 km. It is normally formed by water particles that have condensed around nuclei in the atmosphere.

Heath An open uncultivated lowland area in temperate regions is called heath or heathland. Health usually contains podzol soils.

Heat Island The heat island refers to an urban area where temperatures tend to be higher than those of the surrounding countryside. Escaping heat from buildings, reflection and radiation from concrete, tarmac and bricks, and heat emitted by motor vehicles circulating in the urban area are among the causes for the phenomenon of heat island.

Hercynian Orogeny The term Hercynian orogeny refers to the mountain building episode of carboniferous/ Permian times.

Heterosphere The outer zone of the earth’s atmosphere is called heterosphere. The gaseous constituents of the heterosphere exhibit very low densities.

Hiatus The hiatus refers to a gap in a stratigraphic sequence of rocks, where the missing strata were never deposited or were destroyed by erosion before deposition of the overlying strata.

Hinterland A hinterland is an area that has close economic, social and cultural ties with a central place, such as a port, city or town. In the case of a port, hinterland is the region from which it receives trade or to which it sends goods.

Homoseismal Line (Homoseism) Homoseismal line or homoseism is a line that connects all points of on a map that are affected simultaneously by an earthquake shock. It is synonymous with isoseist.

Homosphere Homosphere is the inner zone of the earth’s atmosphere beneath the heterosphere. The gaseous constituents of the homosphere have higher densities.

Homotaxis Homotaxis refers to those rock strata which occupy the same position in the stratigraphic sequence, although they occur in different regions. Horse Latitudes Horse latitudes refer to the zones of high atmospheric pressure occurring over the oceans in latitudes about 30°-35° Nand 30°-35° 5, i.e, between the belts of the trade winds and the westerlies. They are zones of mainly descending air and are characterised by comparatively dry and stable conditions.

Horst A horst is an elevated block of rock bounded by faults. It has been left upstanding by the sinking of the adjoining land along normal faults or has been uplifted along parallel faults.

Hot Spring (Thermal Spring) Hot spring is a thermal spring that flows out. of the ground with temperatures above 37° C. It is more common in areas of current or recently active vulcanicity, though it is also found in non-volcanic areas. Unlike a geyser, water in a hot spring flows continuously instead of intermittently.

Hum A hum is an isolated hill left as a residual on the floor of a polje. It is named from the village of Hum in the Yugoslavian Karst.

Humidity Humidity is the state of the atmosphere in relation to its water vapour content. It normally refers to relative humidity unless otherwise stated.

Humus Humus is a black or dark-brown organic substaI which is produced by the process of mineralisation a humification within the soil. The formation of hurr requires aerobic conditions in soils. Humus increases s
fertility by providing essential nutrients such as nitrog and trace elements.

Hurricane Hurricane, a term of Spanish derivation, refl primarily to tropical storms of the Caribbean and G: of Mexico. It is accompanied by torrential rain, thunc and lightning. Hurricanes are most frequent in September and October.

Hydration Hydration is a weathering process in whi water is taken up by the mineral of a rock, caus considerable expansion of minerals.

Hydrograph A graph that shows the variation in the lev, velocity or discharge of a body of water with time known as hydrograph.

Hydrosphere The term hydrosphere refers to the tot water surrounding the earth. It includes surface wat oceans, seas, lakes, rivers, ice caps, atmospheric wat and water below the earth’s surface.

Hygrograph Hydrograph is an instrument which recon the changing relative humidity of the atmosphere. The most common type is the hair hydrograph.

Hygrometer Hygrometer is an instrument which mea sun the relative humidity of the atmosphere at any pob in time.

Hygroscopic Nuclei Hygroscopic nuclei refer to particuler of dust, smoke, sulphur dioxide, salts or similar micn scopic substances occurring in the atmosphere aroun which condensation occurs. Condensation commenCE on hygroscopic nuclei before the air is saturated.

Hypsometer Hypsometer is an instrument that is used the determination of altitude or atmospheric pressur by measuring the temperature at which water boils


Geyser A geyser is a violent ejection of hot water and steam that is ejected under pressure from a vent in the earth’s crust. The emission is frequent at regular inter vals. Geysers are associated with past or present vol canic activity. The subterranean structure of a geyser comprises a number of waterfilled chambers intercon­nected with a central pipe. In volcanic regions, ground water percolates beneath the surface region and is heated by the surrounding hot rock. The hot water comes out due to rise in pressure.

Glacier A mass of ice that moves under the influence of gravity along a confined course away from its surface area is called glacier. Glacier has a variety of forms. It is usually of limited width which distinguishes it from a ice-sheet and a ice cap which have larger dimensions.

Glacier Budget Glacier budget refers to the relationship between the amount of snow and ice that is accumulated by a glacier and that lost through meltating or ablation.
Glauconite Glauconite refers to a bluish-green mineral which consists of the hydrous silicate of iron and potassium. It is indicative of a marine origin for the sedimentary rocks in which occurs.

Gneiss The term gneiss refers to a coarse-grained, crystal line (metamorphic) rock with a banded structure. Most gneisses comprise bands of granular quartz and fledspar. Gneisses are formed by the large scale application of heat and pressure during mountain building and vol canic activity. They are mainly of three categories: (i) paragneiss (produced by magmatic alteraHdft of sedi mentary rocks), (ii) orthogneiss (formed by alteration of igneous rocks), and (iii) augengneiss (characterised by eye like swelling of quartz or feldspar crystals).

Gondwana land Gondwana land is the name given to the supercontinent thought to have existed. in the Southern Hemisphere over 200 million years ago following the break up of pangaea. Gondwanaland comprised Antarc tic, Australia and parts of South America, Africa and India. According to A. Wegener, Gondwana land sepa rated from the northern continent of Laurasia by the long narrow ocean of Tethys.

Gorge Gorge is a deep and narrow valley with rocky sidewalls. A gorge is formed by the rejuvenation of river stream (e.g., Rhine Gorge in Germany) or by the downcutting of streams through horizontal rock strata (e.g., Grand Canyon).

Graben A German term, graben refers to a block of rock that has sunk between two roughly parallel faults. A graben is synonymous with a rift valley, if a fault-guided trough is occupied by a valley. It contrasts with a horst.

Granite Granite is an igneous rock of coarse grain and plutonic origin. It consists of quartz (20-40 per cent), feldspar (mainly alkali) and mica. Granites are intrusive rocks and occur in many forms, such as sills, dykes and latholiths. On the basis of their grain size and mineral composition, granites are classified as (i) aplite (finest grains), (ii) pegmatite (coarsest grains), (iii) biotite or muscovite (mica predominates), (iv) hornblende or pyroxene (hornblende or pyroxene are among the constituents of rock), (v) quartz diorite or grandiorite
plagioclase predominates, and (vi) adamalite (plagioclase and alkali feldspar are about in equal amount).

Grassland Grassland is a major type of world vegetation. It is characterised by extensive grassy plains, limited precipitation and a season of drought. Natural grass lands occur in both tropical and temperate latitudes.

Great Circle Great Circle is a circle on the earth’s surface, the plane of which passes through the centre of the earth. The shortest distance between any J;wo points on the earth’s surface is the arc of the Great Circle that passes through them. The equator is also a Great Circle.

Ground Swell The term ground swell refers to waves of great height and length in deep water.

Groundwater Groundwater refers to water that occupies pores, cavities, cracks and other spaces in the rocks beneath the earth. It includes water precipitated from the atmosphere which has percolated through the soil.

Gulf Stream Gulf stream is the name given to a warm current of sea water that originates in the eastern Gulf of Mexico. The southern portion of the Gulf stream is Florida current. The warm Gulf stream combines with the prevailing south-westerly winds to produce the temperate climate of North-West Europe and keeps the Norwegian coast ice-free during the winter months.

Gully A gully is a small but deep channel or raviI\e formed by fluvial erosion. Gullies are not permanently occupied by a stream. They are particularly common in semi-arid areas. Gully erosion is the erosion of soil and rock by the concentration of runoff into gullies.

Guyot A flat-topped variety of a seamount occurring mainly in the Pacific Ocean called guyot. The summits of a guyot may rise up to 3 km from the ocean floor.

ened valleys due to a rising sea level after the melting
of the Pleistocene ice-sheets. Fiords show many char­
acteristics of glaciated V-shaped valleys. They are com­mon in Norway, on the Pacific coast of British Columbia, Canada and South Chile.
Fimification Firnification refers to a combination of pro­cesses in which new snow is transformed into glacier ice, owing to the release of air and a change in
crystallography. ”

Flash Flood A short-lived but rapid rise of water in a river is called flash flood. The quick and sudden rise of water may be due to snowmelt, heavy rainfall, the collapse of an ice-dam, log-jam or artificial dam.

Flood Flood may be defined as the inundation by water of any’ land area not normally covered with water owing to a relatively rapid change of the level of the
particular water body. Floods may Occur due to (i) increase in rainfall, (ii) snowmelt, (iii) rise in water level in lakes, (iv) cyclone, (v) earthquake, and (vi) collapse of dams.

Flood Frequency The term flood frequency refers to a type of data analysis based on flood records in order to determine the probability of flood magnitudes and the
possible recurrence intervals.

Floodplain A floodplain is a low-lying land that borders a river is subjected to periodic flooding. In otrer words, it is that part of a river valley over which a river flows in times of flood. A zone of low relief and gentle gradients, a floodplain is composed of alluvium and – incorporates ox-bow lakes, point bars, abandoned chan­ nels and scrolls.

Florida Current One of the important currents of the North Atlantic Florida current comes as a branch of the north equatorial current which enters the Carribean and then returns to Atlantic Ocean through the Florida Straits as Florida current. Florida current is the southern portion of the Gulf stream.

Fluidisation Fluidisation is defined as the process in which
finely powdered rock material is invaded by an uprising
stream of very hot gas which welds it together and
causes it to flow like a liquid.
Focus (of an Earthquake) The point of origin of an
earthquake within the earth’s crust is called the focus
of the earthquake. Focus of an earthquake is also known
as the hypocentre, the seismic focus and the seismic
origin. An earthwake originating (i) at a depth of more
than 300 km is called a deep focus earthquake, (ii) at
a depth of less than 70 km, a shallow focus earthquake,
and (iii) at depths between 70 km and 300 km, an
intermediate focus earthquake.
Fog Fog is defined as droplets of water suspended in the
lower layers of the atmosphere whose visibility is less
than one kilometre. Fogs result from the condensation
of water vapour around the nuclei of floating dust or
sm9k~ pMticles.
Fohn (Fadm, f9n) Fpftn is a warm and dry wind which
descends On the le~Wi”lf9 sid~ pf P Ipountain range,
especially the Alps in EYfQP@, An ifflpprt~1T).t f=h?racteris­
tic of fohn is the rapid rise of temp!’1n~t~f(;? tpM it
generates, generally more thaft 10″ C in a fgw pour§:
Fohn is mOst common in I>prfn~ l:Utq autl/mo.
Fold Mountains Mountain~ that ‘ fe formeq )’.u1der com­
pression in which the sedimentary rock stra’ta are
squeezed into a succession of synclines and anticlines,
are c~lled fold mountains. Fold mo~ntain~ represr,nt ~p
upland area formed by the buckling of earth’s crust:
Foli~tion The term foliation refers to a laminated or banded
” , “.’ I'”” ,1! ,) ‘”. ‘”
structure within a’ metamorphic rock. Such a structure
is caused by the segregation of diffbrent minerals into
parallef layers due to’ schistosity of th~ r~c~. Fpl~a,tipn
is also defined as the stratiform structure of ice in the
lower layers of a glacier. ‘
Fossil Fossils are the remains of a plant or animal preserved
i~ .sediment~ry rock. Rocks. of ~ s~miiar a~e apq ~H~f,°­
slhonal envIronment possess sImifar fOSS”Ils.
Front A front is ~terin usecfto describ~ a sloping boundary
piarie or surface separating…t.o air masses that exhibit
different meteorojogical properties or characteristics. It
was formerly used for the tropics to describe the ITCZ
but the usage is now restricted to higher latitudes where
thermal discontinuties are much more pronounced.
A cold front is the front that separates a retreating warm
air mass and an advancing cold air mass, which forces
its way underneath “the warm air causing ittq ri’se.
Conversefy, a war~ front !~ the fr~nt that s~.R~f.at~~ ‘I
retre~ti~& cold air ina~s ‘i’\!ld an advancing warm air
mass:,LWhich rises above the cold air. A cold front is
steeper than a warm front and the weath~r a,ssociated
with it tends to pass more rapidly.
Frost Frost refers to a’ weather condition that occurs when
, ,’, ‘ Ie,. :’
the air temperature is at or b~low 0 “~. ~t is “Iso p~fjl1ed
as a weathering agent which ~reak~ up rocks ami (>QH
owing to freezing of the inte.rsfitial water:'” . L’ ‘”
Fuller’s Earth A fine earth similar to a cla~ bl.~t lacking
plasticity is called the fuller’s earth. The fuller’s earth
contains the mineral montmorillonite which enhances its property of taking up water or other fluids.
Funnel Cloud A whirling mass of cloud that forms at the
heart of a tornado or water spout is cajled funnel cloud.
The funnel cloud is a downward ~!rojectiiig’ funnel­
shaped cloud. I ” . u’ ,;’,.

Dalmatian Coast (Concordant CUdst) Dalmatian coast is an .
example of submerged concordant coast, which is a coastline that is parallel to structural grain of the land. It is named after the Dalmatian Coast of Yugoslavia on the Adriatic Sea where this type of coastline occurs.
Dead Cliff A cliff created by marine erosion which has now been abandoned owing to a marine regression or to an accumulation of beach deposits is called dead cliff.
Debris Debris is a French term for ‘wreckage’. It refers to a superficial collection of broken rocks, earth and other inorganic material that has been moved from an original site by streams of water or ice.
Deciduous The term deciduous denotes vegetation that sheds its leaves at the same season every year. In temperate zone, the leaf fall occurs during autumn. In the tropical forests, the fall of leaves may be at any time. The loss of leaves is an adaptation that has evolved as a response to climate and counteracts the effects of seasonal drought or cooler temperature.
Deflation The transportation of fine particles of sand and dust by wind is called deflation. A deflation hollow may form when deflation is concentrated in one area. The Qattara Depression in Egypt is one of the largest examples of deflation holloW.
Delta A delta is a fan-shaped tract of alluvium deposit at the mouth of a river where it deposits more material than can be carried away. A delta is formed by a combination of two processes: (i) sediment is deposited following reduction in the speed of a river as it enters a sea or lake, and (ii) at the same time, in the presence of salt water of the sea the fine clay particles carried in suspension in the river coagulate. Deltas are classified into several types: arcuate delta, bird’s foot delta, cuspate delta, etc.
Dendritic Drainage A drainage pattern consisting of a single main stream with tributaries resembling the branches of a tree is called dendritic drainage. Such a drainage pattern is well developed where underlying rock is of a uniform type, Le., in the region of uniform lithology.
Denudation The wearing away of the land surface is called denudation. Denudation includes the processes of weath ering, mass movemeht, erosion and transportation.
Sometimes, the term denudation is used synonymously with erosion, but this technically does not include weathering.
Deposition The laying down of material that has been weathered, eroded and transported by natural processes is called deposition. Water, wind and ice are the main depositional agents. In terms of volume of material being deposited, rivers are the most important depositionary agent.
Depression The term depression is used to describe an area of relatively low atmospheric pressure found mainly in temperate regions. Depressions are formed when a cold air mass meets a warm air mass along a front. They
are termed deep when the pressure difference between the. centre and the surroundings is great, and shallow when the pressure difference is low.

Desert A desert is an area of the earth’s surface where vegetation and animal life is almost non-existent due to extremely low precipitation. According to one criterion, an area receiving less than 250 mm per year of rainfall is called a desert. Deserts occur mainly in the following locations: (i) the areas of persistent high pressure (e.g., the Sahara), (ii) the areas on the west coast of continents (e.g., the Atacama Desert in Chile), (iii) the continental interiors of the mid-latitudes with high summer and low winter temperatures (e.g., Gobi Desert in Asia).
Detritus The detritus refers to fragmental rocky material produced by the weathering and disintegration of rocks and subsequently moved from its original site.
Dew and Dew Point Dew is defined as the moisture deposited in the form of water droplets on the surface of vegetation and other objects located near to ground level. Dew occurs when the temperature of the ground surface falls and the air in contact with it is cooled below its dew point. Clear night skies, moist air and light winds favour dew formation as they ensure maximum cool~ng by radiation.
Dew point is the temperature of air at which it becomes saturated with water vapour. Below dew point, water vapour starts to condense to form water droplets.
Diastrophism The term diastrophism refers to the large scale deformations of the earth’s crust producing the continents, oceans, mountains, etc: Diastrophism in
cludes folding, faulting, uplift and depH:!ssion .of the. lithosphere, but not vulcanicity.
Discordant Drainage Unlike accordant or antecedent qrain age, discordant drainage is a drainage pattern which has not developed a systematic relationship with the under lying structure.
Distributary A distributary is a separate river channel created when a river splits, but one which does not rejoin the main channel. Distributaries are common in a delta. The term distributary does not describe a braided stream or an anastomosing stream.
Doab A low-lying area of land composed of alluvium that lies between two converging rivers is called a doab. Doabs are characteristic features of the Inqo-Gangetic
plain of North India.. ‘
Doldrums Doldrums are thqse regions of light, variable winds, low pres~ure and ~igh temperature and humidity which occur in tropical or equatorial iatltudes, especially between 5″ Nand 5″ S. They form part of the inter tropical f:onv!:!rgence zone (ITe?:). They occur oy~r the east Pacific, the ~ast Atlantic CJ.rd from the Indian ocean to the west pacific. They are bqHnded to th~ nortt). ard S!?utt). by the trade winds. Their extent varie~ gr~a.t~y with the seasons.
DQJine Tfie t~rm q.oHne refers t8 C1 circylar hQl1q~ o,F depression in the s4rfacl? of J(arstic t~rrijJn: DOHRt y”rie~ in size and is initially caused by solution. It ~;; 4~!:mH¥ the site at which a stream disappears underground.
Donga Donga is a South African term for a steep-sided gully produced by fluvial erosion or by floods. The term is now used especially for gullies formed as a result of soil erosion.
Downs A stretch of open, gently undulating land, especially in chalk areas of southern England is called downs. The term downs also refers to a plain of temperate grassland in the South Island of New Zealand and Australia. In the USA, the term is used to describe an area of coastal sand-dunes.
Drainage aasin A drainage basin is an area of the earth’s surface drained by a single river system and bounded by a watershed. The watershed separates a river from adjoining drainage basins. The size and shape of the drainage basin is controlkd by the geology, str4cture and climate of the region.
Drift Any material derived from the process of glacial erosion is called drift. Thick layers of drift accumulated during the Pleistocene period, but these have since been largely eroded.
Drumlin Drumlin is a Irish term adopted to describe a streamlined elongated hummock or ‘whaleback’ hillock of glacial drift, generally of till. A drumlin has a steeper slope at the llPstream end thin at the downstream end. Although most drumlins show no internal structures, some exhibit a degree of stratification. There are two theories to explain the origin of drumlins: (i) they were formed by deposition of ice around a nucleus of frozen till or rock, and (ii) they were formed by erosion by the ice. Drumlins occur widely in Ireland, Scotland, Wales, and the northern states of the USA.
Dry Valley A river valley which exhibits most of the “t!ributes of a normal valley, but lacks a permanent ri¥@r/stream flow in it is called a dry valley. River valleys occur chiefly in lime~tone or chalk regions.
DuBoy’s Formula In the late 19th century, DuBoy proposed a formula to explain sediment transport in fluids. This formula is called DuBoy’s Formula. According to this formula, the rate of sediment transport in fluids is proportional to excess bed stress above a critical bed stress.
Dujoda The Russian term dujoda refers to a.linear, steep sided depression with an uneven floor developed in a thermoakarst environment.
Dune A mound or ridge of sand found in the deserts and some ,coastal areas is called dune. Dunes are formed by the deposition of particles of sand that have been transported by the wind. Sand dunes are of two forms: crescentic dunes (barchans) and elongated and narrow 4unes (siefs). The form of sand dunes depends on the direction and strength of the ,dominant winds.

Caldera A large basin shaped volcanic crater is called caldera, Caldera forms in one of the followin.& tWe ways: (a) by destruction of the upper part of the vokanic cone by an eruption, of great force

Canyon (Canon) Canyon or canon is the name given to a deep valley/gorge with steep near-vertical sides. It forms by river action, mostly in arid and semi-arid areas, where a river is fed with water from a, distant source. In qmyon, the depth exceeds ttw width consid erably. The most striking canyons are produced in areas of horizontally bedded strata, e.g., the Grand Canyon in USA

Catadasis refers to rock deformation accompa nied by fracture and rotation of mineral grains. A rock formed in this way is termed a cataclasite.

Catchment Area A catchment area is the area from which a single river system collects its water. In other words, it is the area from where the river and its tributaries get most of their water. Water may be in the form of ice, snow or rain. The boundary of a catchment area is defined as the watershed.

Chaparral The term chaparral refers to a form of vegeta tion ctominated by thick-growing evergreen oaks and other trees, with aromatic shrubs. Chaparral occurs in California (USA) and Mexico, where there is a Mediter ranean type of climate. It has evolved in response to mild wet winters and summer drought.

Chelation The process by which rQd~s and soils decompose or disintegrate through the action of organisms or organic substi\nees is called chelation. The organic com P°1.U\(is, known as chelating agents, are extracted from the litter layer by water passing down through it. Chelating agents are richest in heath plants and conifer needles. Chelation plays a major part in the soil process of podzolisation.

Cheluviation Cheluviation is the cor’bination of chelation and eluviation. In cheluviation, water containing organic extracts combines with met{\Uic cations in the soil to , form a chelate. ThQ chelate (a sesquioxide-rich solution) then rn.~W~ downward through the soil profile (hence eluviation).

Chemozem (Tschemosem) Chernozem is a black or dark brown zonal soil that is rich in humus and contains lime. The name chernozem is derived from the Russian term
tschernosem meanin ‘black earth’. Hence chernozem is also called black earth. This soil type is found in a blt tending from Manchuria in China through Russia into Ukraine and into Romania. and Hungary. It is a fertile ,Qit \\no is often used to support cereal crop.

Chestnul Soil Chestnut soil is a zonal (pedocal) soil found on the steppes of the former USSR, the pampas of Argentina, the Great Plains of the USA and the South African veld. Hence, it is a soil of mid~latltude grasslands that occur in drier regions than chernozems. Further, the horizonation of thQ chestnut soils is not as clearly marked i,\s that of the chernozems and it does not develop to such depths. The parent material for chestnut soil is frequently loess.

Chinook Chinook is a warm, dry south-westerly wind which blows down the eastern slopes of the RocKies in parts of North America (specially in Canada and the USA). It is adiabatically warmed and often causes a large rise in temperature. In spring,
Chinook, which is similar to fohn, leads to rapid snowmelt and subsequent avalanches. .

Circum-Pacific Belt The Circum-Pacific belt is a seismic b-elt, which girdles Pacific Ocean. World’s 75 per cent earth quakes occur in this belt. This belt is also characterised by many active volcanoes. Hence. it is popularly called the Ring of Fire. It mostly coincides with the margins of tectonic plates.

Cirque (Corrie, cwm) A deep amphitheatre-shaped rock basin with steep sides and an opening downstream is called cirque. Found in glaciated upland areas, cirques originate as small hollows where snow accumulates. The characteristic shape of

cirques is a result of erosion on the headwall and the rotational slip of the ice within the concave floor of the hollow.

Cirque Glacier A small glacier occupying a glacially eroded armchair-shaped hollow or cirque is called cirque glacier. Cirque glacier may be contained entirely within the reck basin or it may extend outwards beyond the tip of the cirque. It is characterised by a rotational slip.

Cirrocumulus It is a type of cloud occurring between 5,000 and 13,700 m, i.e., at high altitudes. It is white in colour occurring in thin sheets or layers without shading. Due to its resemblance to fish scales, it is sometimes krt°wn as “mackerel sky”.
Cirrostratus Cirrostratus is a high altitude cloud Dccuring between 5,000 m and 13,700 m. It is whitish in colour. The ,cloud produces solar or lunar halo phenomenon.
Cirrus A cloua, white in colour, occuring as silky, fibrous brands or wisps, is called cirrus cloud. Its base can occur between 5,000 m and 13,700 m, Le., at high altitudes. Long-d~awn out wisps known as “maires’ tails” are produced by strong windt in the upper atmosphere.
Cliff A very steep or vertical rock face is called cliff. Cliffs have different forms depending upon factors such as rock type, resistance to erosion, and the presence of bands of weakness. Sea cliffs are formed by wave» undercutting the rock causing its eventual collapse, Near vertical cliffs can also be formed in well-jointed rocks, but where wave-attack k”5 diminished and the cliff foot has been abandoned. Cliffs are a!;>o found in inland areas and in mountainous regions.
Climate The average weather conditions at a specific pla~ over a lengthy period of time (usually at least 30 years) is called climate. The main elements of clhnateare
temperature, atmospheric pressure, wind and humidity. The climate of a particular region is determined by (i) latitude and the tilt of the earth’s axis; (ii) the distribution of land and sea and proximity of ocean currents; (iii) the location of the area in relation to the main circulation belts of the eiirthi and (iv) the altitude and topography of the area.
Climatograph A climatograph 1$ a circular graph depicting seasonal mean-temperature changes plQtted on a monthly basis.
Climograph (Climatogram) A climograph is a graphic diagram to illustrate the general climatic character of a particular place. The diagram is produced by plotting two climatic elements (usually temperature and humid ity) of a place. The result.ant shape of the graph indicates the character of the climate at that place. The term climograph was first used by T. Grifith Taylor.

Crust The crust is the outer most shell of the earth. Lying above the Mohorovicic discontinuity and varying in thickness, it comprises two dominant groups of rocks: sial (continental crust) and sima (oceanic crust). The crust is also sometimes referred to as duricrust.

Cryopedology The scientific study of frost action in soils and the resulting structures is called cryopedology.

Crystalline Rock A rock formed by the process of crystallisation is called crystalline rock. Crystalline rocks include igneous and metamorphic rocks. In an igneous rock, the rate of cooling of magma and the order in which the minerals are crystallised determine the shape and size of crystals. In metamorphic rocks, the shape and size of crystals depends on the mineral itself.

Cuesta Cuesta is a Spanish term that has been widely adopted to describe a ridge with a steep scarp slope (escarpment) and a comparatively dip slope. Cuesta closely reflects the structure of the underlying rocks. It is formed by the differential erosion of gently dipping stra ta.

Cumulus Cumulus is a type of detached, dense cloud. It is greyish in colour when viewed from beneath, but brilliant white where sunlit and seen from the side. In elevation, this cloud type varies between 460 m and 2,000 m. The base of cumulus cloud is horizontal. Cumulus clouds occur mainly in summer and are caused by convection.
Current The current is defined as the permanent or seasonal’ flow of water in a defined direction in the surface water of an ocean, e.g., North Atlantic Drift, Labrador Current, Benguela Current, etc.
Cyclone and Anti-Cyclone Cyclone is a system of low atmospheric pressure in the centre. There are two types of cyclone: the tropical cyclone and the temperate cyclone. Tropical cyclone OCCUlS in the tropical regions, such as Indian Ocean, Indonesia and Australia. In tropical cyclone, the wind rotates in an anti-clockwise direction in Northern Hemisphere and in a clockwise direction in Southern Hemisphere. It is associated with very high speed winds with torrential rainfall. Temper ate cyclone occurs in temperate latitudes. It is now commonly referred to as depression or low.
Anti-cyclone is a system of high atmospheric pressure in the centre and decreasingly low pressure towards the periphery of the system. Air movement is clockwise in Northern Hemisphere and antklockwise in Southern Hemisphere. The associated weather is settled and stable. Two types of anti-cyclone are: (i) cold anti­cyclone (e.g. over Canada and Siberia), and (ii) warm anti-cyclone (e.g. over sub-tropical high pressure belt).
Cyclothem The term cyclothem refers to a series of sedimentary beds deposited during a single cycle of sedimentation. It is indicative of changing environmen tal conditions.
Cymatogeny The term cymatogeny refers to large scale tectonic warping of the crust to produce a type of basin swell structure. In basin-and-swell structure, the crests
of the swells (domes) collapse to form graben (rift valley).

Backwater Backwater is that part of a river which has been bYFassed by the main flow of stream, though still jained to it. Backwater has a very low rate of flow and hence is virtually unmoving or stagnant. It is commonly formed when the neck of a meander is cut through by the stream leaving its old channel.

Badlands The term badland was originally used to describe part of South Dakota (USA), which was a terrain difficult to traverse. It is now used universally to describe any landscape characterised by deep dissection, ravines, gullies, and sharp-edged ridges. Such landscapes are created naturally by fluvial erosion on rocks, or artifi­cially by over-grazing and soil erosion.

Baguio It is a tropical storm experienced in the Philippines. It occurs specially from July to November.

Bahada(Bajada) Bahada (a Spanish term) is a type of alluvial plain, occurring towards the centre of intermon­tane basins in arid or semi-arid areas. It is composed of unconsolidated materials, such as sand, gravel and angular scree, which together mantle the underlying rock-cut pediment. Bahadas or bajadas are formed when several alluvial fans join together to form a gently sloping surface lying between upland areas and playa lakes.

Bai-u season The season of heaviest rain in parts of China and Japan in late spring and summer. Since the rains occur during plum-ripening season Gune-July) in Japan, they are also knawn as plum rains.

Banner cloud Banner cloud is a stationary claud which resembles a banner streaming out on the lee side of a mountain peak. It results from condensatian of air as a maist air-current is farced upwards on the windward side af a sharp peak, such as Malterharn and Everest.

Bar Bar is a depasit of sand ar mud in a river channel. It is also defined as an elangated depasit af sand, shingle or mud in the sea; more or less parallel to the shoreline and sometimes linked to. it. Bars ilre formed by the process of longshare drift. Bars are mainly of two types: (i) tidal’bars, i.e., bars cave red by tides; and (ii) sub­. merged bars, i.e., bars submerged permanently, espe­cially across the mauth af a river ar harbour (harbour ba0. In meteorology, bar is the unit af atmospheric pressure. One bar is equal to a calumn af mercury 750.062 mm high in a barometer.

Barchan (Barkhan) Barchan or barkhan is a crescent-shaped sand dune, the horns af which point away from the directio.n of the dominant wind. In a barchan, the leeward slape is relatively steep and the windward slope gentle. A barchan can only form in a desert region where winds blow almast constantly from one direction. Barchans can vary in height from a few metres to. over 30 metres. They can occur singly or in groups. The Sahara Desert in Africa and Turkistan .in Central Asia possess the best examples af barchans.

Barometer Barometer is an instrument for measuring atmaspheric pressure. The necessary barometer was invented by Taricelli in 1643. It measures the height of a column that the atmosphere is able to support in a vertical glass tube.

Barrier Beach (Barrier island) Barrier beach is an offshore sandy bar that lies abave high-tide level, usually sepa­rated from the caast by a lagoon. When an offshore sandy bar is sufficiently high above high-tide level and has dunes lying on it, it is termed barrier island. Barrier beaches and islands are cammon on relatively shallow gently sloping offshore areas. Palm Beach and Miami Beach in the USA are some of the best examples l1f barrier beaches.

Barysphere Barysphere refers to all of the earth’s i~terior which lies beneath the lithosphere. Hence, it irteilides the core, the mantle and asthenosph~f~. However, some geographers have uslKl the term loosely to describe only the core or only the mantle.

Basic Rock An igneous rock that is quartz free and eonlains a low percentage of silica is called basic rock. A basic rock is composed of minerals such as caldum feldspars. Basic rocks are classified into tilttaba~ic rocks (decrease in the amount of feldsJYar) and intermediate rocks (increase in the sodium content of feldspar). Basalt; dolerite and gabbro are examples of bask rocks.

Basisol Basisol is a type of tropical soil. It is characterised by its blackness, its low organic content and its accu­mulation of calcium carbonate in the form of a concre” tion honzon. Basisol is formed from the wealhering of basalt under humid tropical conditions. It is cOmmon in the trap landscape of the Indian Ocean.

Batholith (Bathylith) Batholith is a very large dome”shaped intrusion of igneous rock (usually granite) several kilometres in depth and extending over hundreds of square kilometres. Batholiths are always associated with an area where mountain building has taken place. They are formed either by gradual igneous replatemei’lt of he country-rock at great depth (the process is termed as granitisation) or by stopping during a mountain­building period (called orogeny). Dartmoor; Devon and Mourne mountains in Nodhen\ Ireland are typical examples of exposed batholiths.

Bathyal Zone The zone of the ocean on the continental
slope is called bathyal zone. Bathayal zone lies between the shallow neritic zone and the deeper abyssal zone. Despite the absence of light, there is a flourishing and varied animal life (benthos) in this zone.

Bay A bay is a wide curving indentation made by the sea or a lake in a coast line, usually lying between two headlands. Sometimes, in local context, the term bay is also used to describe the extension of lowland into an upland area.

Beach A beach is an area at the junction at the junction of the land and the sea. It is located on an eroded platform of solid rock, the wave-cut platform, and is generally of a low gradient with a gently concave profile. It is defined as accumulations of materials lying between the lowest level of spring tides and the highest level reached by storm waves. The materials consist of a wide range of particles, from large rock fragments, shangle and sand to fine mud and silt.

Benguela Current It is an ocean current flowing north­wards off the coast of South-West Africa. It is characterised by the upwelling of relatively cold water and has an associated effect on the coastal climate of the region.

Benioff zone Named after H. Benioff, Benioff zone extends at an angle of about 45″ from the base of an ocean trench. Benioff zone marks the edge of two plate margins where one is overridden by another during the process of subduction (plate tectonics).

Behtl\t)s the term benthos refer~ to life dwelling on the sea-floor. Benthos occur in numerous forms. Sessile benthtl~ ~re fixed to the sea-floor, while vagrant benthos are capable of active movement on or within the sediment.
Bergschrund A dt!~j); narrow crack near the back of a cirqUe glati~f is cailed bergschrund. B~rgschrund marks the Hhe along which a glacier moves away from the cinjue;s backwall.

tHome Biome is a major community of flora and fauna of a region. It generally refers to a climatic region having similar vegehHidh. The ten principal biomes of the world are: mountain and polar regions, tropical rain forest, grasslands, deserts, temperate forests, monsoon forests, deciduous forests,coniferous forests and evergreen shrub forests.

Bltt:tf§ Foo~ Delta A type of delta that extends out into the sea in a fihger-like pattern with sediment deposited on either side of the distributary streams is called bird’s foot delta. Such deltas are composed of very fine sediments (largely silt) and develop in conditions where currents clnd tides are relatively weak. The Mississippi Delta in the USA is one of the best examples of the bird’s foot delta.

Blirtd Valley Blind valley is a characteristic of limestone regions (Karstic regions). It ends abruptly with a rock wall when its stream disappears underground through a cave or sink-hole.

Blizzard Blizzard is an intensely cold and strong wind accompanied by falling snow. The snow is often whipped up from the ground and visibility is considerably reduced. It is particularly prevalent in Antarctica.

Block Mountain A block mountain is an area of high relief which is bounded on most sides by faults and which has either been uplifted by earth movement or left elevated by the sinking of surrounding areas. The Vosges mountain (France) and Black Forest (Germany) are examples of block mountains.

Blood-Rain Raindrops which contain fine red dust, brought by upper winds from neighbouring desert areas, are called blood-rains. For example, Sahara dust often causes blood-rains over Italy.

Blossom Showers (Mango Showers) Blossom showers or mango showers are the rain showers that occur from March to May in the monsoon region of South-east Asia.

Bluff The term bluff denotes a river-cut cliff or steep slope on the outside of a meander. A line of bluffs often marks the edge of a former flood plain. Bluffs are produced by rivers eroding laterally by cutting into the valley sides.

Bog Bog is general term for morass or swamp. It is also a commonly used term in Scotland and Ireland for a stretch of waterlogged, spongy ground, chiefly com­posed of decaying vegetable matter. Bogs are wide­spread in Russia, Scandinavia and Canada. A bog often forms with the growth of moss, especially sphagnum, on the surface of a shallow pond or lake.

Bora A cold, dry northerly or northeasterly wind that blows down through the mountains to the eastern coast of the Adriatic Sea and North Italy is named bora.

Absolute Humidity The amount of water vapour per unit volume of air is called absolute humidity. In other words, absolute humidity is the density of water vapour present in a mixture of air and water vapour, Le., ratio of the mass of water vapour to the volume occupied by the mixture. It is expressed in grams per cubic centimetre (gcm-1). Cold air has a lower absolute humidity than warm air.

Abyssal Plain Also known as deep-sea plain, abyssal plain is generally the level area of the ocean floor which lies between about 3,500 m and 5,500 m below the surface of the ocean. Features such as trenches, mid-ocean ridges, sea-mounts, etc., often break the regularity of the abyssal plain. Abyssal plain is composed of ooze or red clay. In this plain, sea temperatures do not exceed 4″ C.

Acid Rain When the rain is contaminated by either sulphur oxides (caustic gases emitted mostly by coal combus­tion) or by a combination of sulphur dioxide and
nitrogen oxide (smog emitted from motor vehicle exhaust), it is termed as acid rain. Acid rain has a pH value of less than 5.6 and is capable of burning holes in leafy vegetation, and causing considerable damage to the environment.

Acid Rock It is an igneous rock that is very rich in silica (over 60 per cent), over 10 per cent of which are free quartz, and aluminium. Acid rocks are relatively light and form the main material of the continents. Granite, granodiorites, obsidian and rhyolites are the typical examples of acid rocks.

Actinometer Actinometer is a device that measures solar radiation. The instrument which records solar radiation is known as actinograph.

Adiabatic Process It is an atmospheric process in which changes take place in the pressure and volume of a body of gas (air) without an actual loss or gain of heat from outside. As a result, the temperature of the air mass changes. Adiabatic changes normally occur in an ascend­ing or descending air mass. When a parcel of air rises, its volume increases due to a decrease in pressme. With decrease in volume, temperature of air also decreases. The rate at which temperature decreases in rising air is called the adiabatic lapse rate. For a saturated rising air, the fall of temperature is checked by the release of latent heat of condensation. A reverse process occurs when an air parcel descends.

Advection Advection is the horizontal movement of an air mass across the earth’s surface. The transfer of heat from low to high latitudes is the most obvious example of advection. Advection is specially important when the air mass is moving from a different source area and is bringing in different conditions of humidity and tem­perature. Advection is opposite to convection.

Aeolian (Eolian) The term aeolian or eolian denotes the processes or landforms caused by or related to the wind. Ventifact, yardang, zeugen, etc., are the examples of
aeolian erosion, while dunes, loess, etc., are the ex­amples of aeolian deposition. The aeolian processes are most common in arid environments, such as hot and cold deserts, and on exposed shorelines.

Aerology Aerology is the scientific study of all the atmo­sphere above the surface layers. Aeronomy, a branch of aerology, is the scientific study of the atmosphere above 50 km where dissociation and ionisation of gas molecules occur.

Aerosols The aerosol is often used to describe minute particles (solid and liquid) suspended within the gas. Sea­salt, dust (particularly silicates), organic matter, smoke, carbon, lead and aluminium compounds are examples of aerosols. Aerosols enter the atmosphere by both natural processes, such as vulcanicity, and by human agency, such as the burning of fossil fuels. Due to their presence in the atmosphere as dust veil, aerosols lower the amount of solar radiation reaching the earth. Hence, their overall thermal effect is probably one of cooling, counteracting the greenhouse effect.

Agate Occurring in cavities in volcanic and some other rocks, agate is a semi-precious stone. Agate consists of a type of silica (chalcedony).

Aggradation Aggradation is the process by which a land surface is built up by the deposition of debris and other solid materials by rivers or seas. River-borne aggrada­tion is more common. Aggradation usually results due to a reduction in the river’& load-bearing capacity. Such reduction may be due to several factors; such as an increase in the amount of debris supplied to the river; a loss of speed or volume of flow; and a rise in the base level.

Aiguille Aiguille is a French term which is widely adopted to describe narrow, needle-shaped rocks. Such rocks are particularly well developed in the Chamonix region 0.£ the European Alps.

Air Mass A mass of air with similar properties of tempera­ture and moisture covering a large area of the earth’s surface is called/air mass. According to the nature of their source regions, air masses may be classified as Arctic, Antarctic, Polar, tropical or equatorial. This clas­sification is based on temperature characteristics of air masses. On the basis of its humidity, an air mass is classified as maritime, continental or monsoonal. A combination of these characteristic gives tropical mari­time air mass, polar continental air mass, polar conti­nental monsoonal air mass, etc.
Aleutian Current It is a cold ocean current of the North Pacific Ocean.

Aleutian Low Located over the Aleutian Island of the North Pacific ocean, Aleutian low is one of the cells in the semi­permanent zone of subpolar low pressure. It is not a stationary low pressure system but represents an ag­gregate of deep depressions. It is more marked in winter than in summer. ­

Alluvial Cone Alluvial cone is a cone-shaped accumulation of thick, coarse alluvial material which is transported by ephemeral or short-lived torrents emerging fmm a high rocky massif at a mountain front or valley side: It is similar to, but steeper than an alluvial fan. Alluvial cone is more typical of arid and semi-arid areas where torrents carrying large loads are abruptly checked on entering a main valley or plain.

Alluvial Fan Alluvial fan is a fan-shaped landform com­posed of alluvium, consisting of sand and gravel (i.e., finer material than in an alluvial cone). An alluvial fan is formed at a place where a constricted river enters a main valley or emerges from mountains onto a plain. The apex of the fan is located at the point at which the river emerges. It is the thickest part of an ‘alluvial fan. Fans of the upper Rhone valley in Switzerland are typical examples of alluvial fans.

Alluvium It is a sedimentary material deposited by a river along its course. Such a deposition may be in the forms at cones, fans, deltas and flood plains. Alluvium is characterised by: (i) sorting, so that coarser alluvium is
found in the upper course of rivers and finer in the lower courses; (ii) stratification, such that coarse material in river bars is overlain by finer material; and (iii) structures such as current bedding. Alluvial deposits are agriculturally fertile, though subject to flooding. These deposits can contain important minerals, such as gold, platinum and diamonds.

Almwind It is a local wind of the fohn variety which blows across the Tatra mountains. It descends as a warmer wind onto the plains of South Poland in spring, causing avalanches.

Alpine The term alpine refers to or belonging to the Alps mountain. It is also used to refer to the physical features (such as relief, climate, soils, ete.) of mid-latitude moun­tain environments.

Altimeter It is an instrument which indicates height above sea level, i.e., altitude. Pressure altimeter and radio altimeter are the two main types of altimeter. The pressure altimeter is a form of aneroid barometer that measures changes in atmospheric pressure with height. Radio altimeter measures the time taken by radio waves from an aircraft to reflect back from the earth’s surface.

Altrimetric Frequency Analysis It is a technique used in analysing the relief of an area by map analysis. The method involves noting all the summit spot-heights shown on the map and plotting them on a bar chart. The horizontal axis on the graph represents altitude above sea-level, while vertical axis represents the per­centage frequency of the summits. The method is not used on a large scale today.

Altocumulus Altocumulus is a type of cloud that occurs in bands or waves. Such clouds are often separated by blue sky. Altocumulus clouds occur at about 2,000-7000 m, i.e., at middle altitudes, in temperate latitudes. They are usually a sign of fair weather.

Altostratus Altostratus is a type of cloud occurring at middle altitudes, i.e., between 2,000-7,000 m. It is com­posed of either ice particles or water droplets or a mixture of both. It usually forms a greyish sheet covering much of the sky. Altostratus is associated with a warm front, and is often a precursor of rainy water.

Anemometer Any instrument that measures wind speed is called anemotneter. The most common anemometer is the Clip anemometer. Other types of anemometer include pressure-tube anemometer, pressure-plate an­emometer hot-wire anemometer, anemograph (an an­emometer that automatically records wind speed on a continuous trace) and sonic anemometer (an anemom­eter based on the theory that an ultrasonic pulse travels through air at speed of 340 fils).

Antecedent Drainage (Antecedence) A drainage system that has maintained its direction of flow despite tectonic, uplift or folding of land across its course is called antecedent drainage or antecedence. An antecedent riVer is able to maintain its direction due to the fact that the rate of downcutting of such river is approximately equal to the rate of crustal uplift. Antecedent rivers generally cross the uplifted mountains and plateaus by means of deep gorges. The Colorado river of the USA and the Indus, Brahmaputra and the Ganges rivers in India are typical examples of antecedent drainage.

Anticline and Syncline Anticlines and synclines result from compressional forces acting on the rocks. Anticline is a rock structure in which the beds of rock are folded into an arch, i.e., the beds dip outwards from the crest, the oldest rocks occurring in the core. Anticlines alternate with synclines in which the strata dip towards each other. An upfold is an anticline, while a downfold is a syncline.

Apehelion and Perihelion Aphelion is the furthest point of heavenly body or planet (including our earth) from the sun during its orbit. In the case of the ear~h, aphelion occurs on July 4, when the sun-earth distance is 152 million km, which is 1.5 per cent greater than the annual mean distance between the two. Perihelion is the nearest point to the sun reached by a ‘heavenly body during its orbit. In case of the earth, this occurs on January 3 when the sun-earth distance is 147.3 million km.

Apogee Apogee is defined as the meridianal altitude of the sun at midday on the longest day of the year. Apogee is also defined as the point in the orbit of a planet when it is farthest away from the earth.

Aquifer Acquifer is a rock layer sufficiently porous to absorb water and allow it to pass freely through. If it is underlain by a layer of impermeable rock, water p.assed will not be downwards, but directed laterally. If the stratum is bounded on its upper surface by an impermeable rock layer, it is termed a confined acquifer.

Arcuate Delta It is a type of delta which is fan-shaped. Its rounded margin extends into the sea. The fan shape of such delta is a result of the division and subdivision of channels. Nile Delta is a classic example of arcuate delta.

Artesian Basin/Well An artesian basin is a geological structure in which the beds dip toward a central point’
forming a basin with a permeable layer of aquifer (a rock) sandwiched between impermeable rocks. London Basin in UK is a good example of an artesian basin. An artesian well is a well sunk into an artesian basin. Water of an artesian well is forced upwards to the ground surface by hydrostatic Fressure, if the point at which the well is sunk lies below the water-table level in the aquifer. In many arid and semi-arid regions, such as parts af Australia and the USA, artesian wells are the main saurce af Water.

Asthenosphere Asthenasphere is a gealagical term to’ denate the zane af the earth’s mantle, which lies immediately belaw the lithasphere. Asthenasphere has paar rigidity and rock strength. Hence it is capable of producing pralanged deformatian. According to’ gea­physicists, harizantal canvectian flaw in asthenasphere may be a cause af mavement af the plates af the auter lithasphere (plate tectanics). Asthenasphere is thaught to. be campased af partially malten peridatite.

Atmosphere Atmasphere is the layer af gases envelaping the earth. It is compased af nitrogen, axygen, argan, carban diaxide and variaus ather gases. Over 95 per cent af the atmasphere lies within abaut 30 km af the surface af the earth; thaugh its auter limit extends to. abaut 10,000 km. There are several layers af atma­sphere, such as tropasphere, stratasphere and mesas­phere.

Atoll An atall is a ring-shaped island reef that encircles a central layer af sea water in which detrital material callects. It is campased largely af coral but in same aceanic atalls certain calcareaus algae may farm the bulk af the reef. It is a particularly camman feature af the
Pacific Ocean.

Attrition The wearing dawn af rack particles by ather rock particles while being transparted by water, wind or ice, is called attritian. Through attritian, particles become gradually smaller, smaather and mare rounded, e.g., beach pebbles.

Aurora Aurara is a luminaus phenamenan seen in the sky at high latitudes. It is manifested as streamers, veils, sheets and rays at heights af abaut 100 km in the night sky. It is thaught to. result from magnetic starms and salar dischar~s during peri ads afhigh sun-spat activity. Aurora is knawn as the auorara borealis ar Ilorthem lights in the Narthern Hemisphere ?nd as aurora austrlis ar sOl/them lights in the Sauchern – Hemisphere.

Avalanche A slide ar horizantal fall af a mass 6f snaw and ice in mauntainaus areas is called avalanche. Ava­lanches accur when snaw and ice accumulate to. such an extend that the mass is unable to. suppart itself and hence slides under the influence af gravity. Avalanches are classified into. a number af types based an different variables such as type af breakaway (laase snaw ar slab); humidity of snaw (dry ar wet); pasitian af sliding surface; form af track: and farm af mavement.

Azonal Soil Also. knawn as skeletal sail, azanal sail is a sail type in which the sail profile is underdevelaped and there has been little ar no. differentiatian into. separate sail harizans. Azanal sails are aften young. These sail are subdivided into. lithasal, regasal and alluvial sails.