Physical Geography Dictionary and Glossary | A to Z | UPSC – IAS
Geography terms and Definitions starting with A | UPSC – IAS
Ablation – Wastage of glacial ice through melting and sublimation.
Ablation zone The lower portion of a glacier where there is a net annual loss of ice due to melting and sublimation.
Absolute humidity One measure of the actual water vapor content of air, expressed as the mass of water vapor in a given volume of air, usually as grams of water per cubic meter of air.
Absorption The ability of an object to assimilate energy from electromagnetic waves that strike it.
Accumulation (glacial ice accumulation) Addition of ice into a glacier by incorporation of snow.
Accumulation zone The upper portion of a glacier where there is a greater annual accumulation of ice than there is wastage.
Acid rain Precipitation with a pH less than 5.6. It may involve dry deposition without moisture.
Adiabaticcooling Cooling by expansion, such as in rising air.
Adiabatic warming Warming by compression, such as in descending air.
Adret slope A slope oriented so that the Sun’s rays arrive at a relatively high angle. Such a slope tends to be relatively warm and dry.
Advection Horizontal transfer of energy, such as through the movement of wind across Earth’s surface.
Aeolian processes Processes related to wind action that are most pronounced, widespread, and effective in dry lands.
Aerosols Solid or liquid particles suspended in the atmosphere; also called particulates.
Aggradation The process in which a stream bed is raised as a result of the deposition of sediment. A horizon Upper soil layer in which humus and other organic materials are mixed with mineral particles.
Air mass An extensive body of air that has relatively uniform properties in the horizontal dimension and moves as an entity.
Albedo The reflectivity of a surface. The fraction of total solar radiation that is reflected back, unchanged, into space.
Alfisol A widely distributed soil order distinguished by a subsurface clay horizon and a medium-to-generous supply of plant nutrients and water.
Alluvialfan A fan-shaped depositional feature of alluvium laid down by a stream issuing from a mountain canyon.
Alluvium Any stream-deposited sedimentary material.
Alpine glacier Individual glacier that develops near a mountain crest line and normally moves down-valley for some distance.
Andisol Soil order derived from volcanic ash. angiosperms Plants that have seeds encased in some sort of protective body, such as a fruit, a nut, or a seedpod.
Angle of incidence The angle at which the Sun’s rays strike Earth’s surface.
Angle of repose Steepest angle that can be assumed by loose fragments on a slope without downslope movement.
Annual plants (annuals) Plants that perish during times of environmental stress but leave behind a reservoir of seeds to germinate during the next favorable period.
Antarctic Circle The parallel of 66.5° south latitude.
Antecedent stream Stream that predates the existence of the hill or mountain through which it flows.
Anticline A simple symmetrical upfold in the rock structure.
Anticyclone A high-pressure center.
Antitrade winds Tropical upper-atmosphere westerly winds at the top of the Hadley cells that blow toward the northeast in the Northern Hemisphere and toward the southeast in the Southern Hemisphere.
Aphelion The point in Earth’s elliptical orbit at which Earth is farthest from the Sun (about 152,100,000 kilometers or 94,500,000 miles).
Aquiclude An impermeable rock layer that is so dense as to exclude water.
Aquifer A permeable subsurface rock layer that can store, transmit, and supply water.
Arctic Circle The parallel of 66.5° north latitude.
Arête A narrow, jagged, serrated spine of rock; remainder of a ridge crest after several glacial cirques have been cut back into an interfluve from opposite sides of a divide.
Aridisol A soil order occupying dry environments that do not have enough water to remove soluble minerals from the soil; typified by a thin profile that is sandy and lacking in organic matter.
Artesian well The free flow that results when a well is drilled from the surface down into the aquifer and the confining pressure is sufficient to force the water to the surface without artificial pumping.
Asthenosphere Plastic layer of the upper mantle that underlies the lithosphere. Its rock is dense, but very hot and therefore weak and easily deformed.
Atmosphere The gaseous envelope surrounding Earth.
Atmospheric pressure The force exerted by the atmosphere on a surface.
Atoll Coral reef in the general shape of a ring or partial ring that encloses a lagoon.
Average annual temperature range Difference in temperature between the average temperature of the hottest and coldest months for a location.
Average lapse rate The average rate of temperature decrease with height in the troposphere—about 6.5° C per 1000 meters (3.6° F per 1000 feet).
Geography terms and Definitions starting with B | UPSC – IAS
Backwash Water moving seaward after the momentum of the wave swash is overcome by gravity and friction.
Badlands Intricately rilled and barren terrain of arid and semiarid regions, characterized by a multiplicity of short, steep slopes.
Bajada A continual alluvial surface that extends across the piedmont zone, slanting from the range toward the basin, in which it is difficult to distinguish between individual alluvial fans.
Barchandune A crescent-shaped sand dune with cusps of the crescent pointing downwind.
Barometer Instrument used to measure atmospheric pressure.
Barrierisland Narrow offshore island composed of sediment; generally oriented parallel to shore.
Barrierreef A prominent ridge of coral that roughly parallels the coastline but lies offshore, with a shallow lagoon between the reefs and the coast.
Basalslip The term used to describe the sliding of the bottom of a glacier over its bed on a lubricating film of water.
Basalt Fine-grained, dark (usually black) volcanic rock; forms from mafic (relatively low silica content) lava.
Baselevel An imaginary surface extending underneath the continents from sea level at the coasts and indicating the lowest level to which land can be eroded.
Batholith The largest and most amorphous of igneous intrusions.
Baymouth bar A spit that extends entirely across the mouth of a bay, transforming the bay into a lagoon.
Beach An exposed deposit of loose sediment, normally composed of sand and/or gravel, and occupying the coastal transition zone between land and water.
Beach drifting The zigzag movement of sediment caused by waves washing particles onto a beach at a slight angle; the net result is the movement of sediment along the coast in a general downwind direction.
Bedding plane Flat surfaces separating one sedimentary layer from the next.
Bedload Sand, gravel, and larger rock fragments moving in a stream by saltation and traction.
B horizon Mineral soil horizon located beneath the A horizon.
Biodiversity The number of different kinds of organisms present in a location.
Biogeography The study of the distribution patterns of plants and animals, and how these patterns change over time.
Biological weathering Rock weathering processes involving the action of plants or animals.
Biomass The total mass (or weight) of all living organisms in an ecosystem or per unit area.
Biome A large, recognizable assemblage of plants and animals in functional interaction with its environment.
Biosphere The living organisms of Earth.
Biota The total complex of plant and animal life.
Blowout (deflation hollow) A shallow depression from which an abundance of fine material has been deflated by wind.
Boreal forest (taiga) An extensive needleleaf forest in the subarctic regions of North America and Eurasia.
Braided channel pattern (braided stream) A stream that consists of a multiplicity of interwoven and interconnected shallow channels separated by low islands of sand, gravel, and other loose debris.
Broadleaf trees Trees that have flat and expansive leaves.
Butte An erosional remnant of very small surface area and clifflike sides that rises conspicuously above the surroundings.
Geography terms and Definitions starting with C | UPSC – IAS
Calcification One of the dominant pedogenic regimes in areas where the principal soil moisture movement is upward because of a moisture deficit. This regime is characterized by a concentration of calcium carbonate (CaCO3) in the B horizon, forming a hardpan.
Caldera Large, steep-sided, roughly circular depression resulting from the explosion and/or collapse of a large volcano. capacity (stream capacity) The maximum load that a stream can transport under given conditions.
Capacity (water vapor capacity) Maximum amount of water vapor that can be present in the air at a given temperature.
Capillarity The action by which water can climb upward in restricted confinement as a result of its high surface tension, and thus the ability of its molecules to stick closely together.
Carbonation A process in which carbon dioxide in water reacts with carbonate rocks to produce a very soluble product (calcium bicarbonate), which can readily be removed by runoff or percolation, and which can also be deposited in crystalline form if the water is evaporated.
Carbon cycle The change from carbon dioxide to living matter and back to carbon dioxide.
Carbon dioxide CO2 (Greenhouse) – minor gas in the atmosphere; one of the greenhouse gases; by-product of combustion and respiration.
Cation exchange capacity (CEC) Capability of soil to attract and exchange cations.
Cavern Large opening or cave, especially in limestone; often decorated with speleothems.
Chemical weathering The chemical decomposition of rock by the alteration of rock-forming minerals.
Chinook A localized downslope wind of relatively dry and warm air, which is further warmed adiabatically as it moves down the leeward slope of the Rocky Mountains.
Chlorofluorocarbons(CFCs) Synthetic chemicals commonly used as refrigerants and in aerosol spray cans; destroy ozone in the upper atmosphere.
C horizon Lower soil layer composed of weathered parent material that has not been significantly affected by translocation or leaching.
Cinder cone Small, common volcano that is composed primarily of pyroclastic material blasted out from a vent in small but intense explosions. The structure of the volcano is usually a conical hill of loose material.
Circle of illumination The edge of the sunlit hemisphere that is a great circle separating Earth into a light half and a dark half.
Cirque A broad amphitheater hollowed out at the head of a glacial valley by glacial erosion and frost wedging.
Cirque glacier A small glacier confined to its cirque and not moving down-valley.
Cirruscloud High cirriform clouds of feathery appearance.
Clay Very small inorganic particles produced by chemical alteration of silicate minerals.
Climate An aggregate of day-to-day weather conditions and weather extremes over a long period of time, usually at least 30 years.
Climax vegetation A stable plant association of relatively constant composition that develops at the end of a long succession of changes.
Climograph (climatic diagram) Chart showing the average monthly temperature and precipitation for a weather station.
Cloud Visible accumulation of tiny liquid water droplets or ice crystals suspended in the atmosphere.
Col A pass or saddle through a ridge produced when two adjacent glacial cirques on opposite sides of a divide are cut back enough to remove part of the arête between them.
Cold front The leading edge of a cool air mass actively displacing warm air.
Collapsesinkhole A sinkhole produced by the collapse of the roof of a subsurface cavern; a collapse doline.
Colloids Organic and inorganic microscopic particles of soil that represent the chemically active portion of particles in the soil.
Competence (stream competence) The size of the largest particle that can be transported by a stream.
Compositevolcano Volcanoes with the classic symmetrical, cone-shaped peak, produced by a mixture of lava outpouring and pyroclastic explosion; also stratovolcano.
Compromise map projection A map projection that is neither conformal or equivalent, but a balance of those, or other, map properties.
Condensation Process by which water vapor is converted to liquid water; a warming process because latent heat is released.
Condensation nuclei Tiny atmospheric particles of dust, bacteria, smoke, and salt that serve as collection centers for water molecules.
Conduction The movement of energy from one molecule to another without changing the relative positions of the molecules. It enables the transfer of heat between different parts of a stationary body.
Cone of depression The phenomenon whereby the water table has sunk into the approximate shape of an inverted cone in the immediate vicinity of a well as the result of the removal of a considerable amount of groundwater.
Conformal map projection A projection that maintains proper angular relationships over the entire map; over limited areas shows the correct shapes of features shown on a map.
Conic projection A family of maps in which one or more cones is set tangent to, or intersecting, a portion of the globe and the geographic grid is projected onto the cone(s).
Contact metamorphism Metamorphism of surrounding rocks by contact with magma.
Continental drift Theory that proposed that the present continents were originally connected as one or two large landmasses that have broken up and drifted apart over the last several hundred million years.
Continental ice sheet Large ice sheet covering a portion of a continental area.
Continental rift valley Fault-produced valley resulting from spreading or rifting of continent.
Controls of weather and climate The most important influences acting upon the elements of weather and climate.
Convection Energy transfer through the vertical circulation and movement of fluids, such as air, due to density differences.
Convection cell Closed pattern of convective circulation.
Convective lifting Air lifting with showery precipitation resulting from convection.
Convergent [plate] boundary Location where two lithospheric plates collide.
Convergent lifting Air lifting as a result of wind convergence.
Coriolis effect (Coriolis force) The apparent deflection of free-moving objects to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, in response to the rotation of Earth.
Creep (soil creep) The slowest and least perceptible form of mass wasting, which consists of a very gradual downhill movement of soil and regolith.
Crust The outermost solid layer of Earth.
Cryosphere Subsphere of the hydrosphere that encompasses water frozen as snow or ice.
Cultural geography The study of the human and/or cultural elements of geography.
Cumulonimbus cloud Tall cumulus cloud associated with rain, thunderstorms, and other kinds of severe weather such as tornadoes and hurricanes.
Cumulus cloud Puffy white cloud that forms from rising columns of air.
Cutoff meander A portion of an old meandering stream course left isolated from the present stream channel because the narrow meander neck has been cut through by stream erosion.
Cyclone Low-pressure center.
Cylindrical projection A family of maps derived from the concept of projection onto a paper cylinder that is tangential to, or intersecting with, a globe.
Geography terms and Definitions starting with D | UPSC – IAS
Daylight-saving time Shifting of clocks forward one hour.
Debris flow Stream-like flow of dense, muddy water heavily laden with sediments of various sizes; a mudflow containing large boulders.
December solstice Day of the year when the vertical rays of the Sun strike the Tropic of Capricorn; on or about December 21; winter solstice in the Northern Hemisphere.
Deciduous tree A tree that experiences an annual period in which all leaves die and usually fall from the tree, due either to a cold season or a dry season.
Decomposers Mainly microscopic organisms such as bacteria that decompose dead plant and animal matter.
Deflation The shifting of loose particles by wind blowing them into the air or rolling them along the ground.
Delta A landform comprised of alluvium at the mouth of a river produced by the sudden reduction of a stream’s velocity and the resulting deposition of the stream’s load.
Dendritic drainage pattern A treelike, branching pattern that consists of a random merging of streams, with tributaries joining larger streams irregularly, but always at acute angles; generally develops in regions where the underlying structure does not significantly control the drainage pattern.
Dendrochronology Study of past events and past climate through the analysis of tree rings.
Denitrification The conversion of nitrates into free nitrogen in the air.
Denudation The total effect of all actions (weathering, mass wasting, and erosion) that lower the surface of the continents.
Desert Climate, landscape, or biome associated with extremely arid conditions.
Desert pavement Hard and relatively impermeable desert surface of tightly packed small rocks.
Desert varnish A dark shiny coating of iron and manganese oxides that forms on rock surfaces exposed to desert air for a long time.
Dew The condensation of beads of water on relatively cold surfaces.
Dew point temperature (dew point) The critical air temperature at which water vapor saturation is reached.
Differential weathering and erosion The process whereby different rocks or parts of the same rock weather and/or erode at different rates.
Digital elevation model (DEM) Computer-generated shaded-relief image of a landscape derived from a database of precise elevation measurements.
Dike A vertical or nearly vertical sheet of magma that is thrust upward into preexisting rock.
Disappearing stream Stream that abruptly disappears from the surface where it flows into an underground cavity; common in karst regions.
Dissolution Removal of bedrock through chemical action of water; includes removal of subsurface rock through action of groundwater.
Dissolved load The minerals, largely salts, that are dissolved in water and carried invisibly in solution.
Divergent [plate] boundary Location where two lithospheric plates spread apart.
Doldrums Belt of calm air associated with the region between the trade winds of the Northern and Southern hemispheres, generally in the vicinity of the equator. The region of the intertropical convergence zone (ITCZ).
Downcutting Action of stream to erode a deeper channel; occurs when stream is flowing swiftly and/or flowing down a steep slope.
Drainage basin An area that contributes overland flow and groundwater to a specific stream (also called a watershed or catchment).
Drainage divide The line of separation between runoff that descends into two different drainage basins.
Drift (glacial drift) All material carried and deposited by glaciers.
Drumlin A low, elongated hill formed by ice-sheet deposition and erosion. The long axis is aligned parallel with the direction of ice movements, with the blunt, steeper end facing the direction from which the ice came.
Dry adiabatic rate(dry adiabatic lapse rate) The rate at which a parcel of unsaturated air cools as it rises (10°C per 1000 meters [5.5°F per 1000 feet]).
Dynamic high High-pressure cell associated with prominently descending air.
Dynamic low Low-pressure cell associated with prominently rising air.
Geography terms and Definitions starting with E | UPSC – IAS
Earthflow Mass wasting process in which a portion of a water-saturated slope moves a short distance downhill.
Earthquake Vibrations generated by abrupt movement of Earth’s crust.
Easterly wave A long but weak migratory low-pressure trough in the tropics.
Ebb tide A periodic falling of sea level during a tidal cycle.
Ecosystem The totality of interactions among organisms and the environment in the area of consideration.
Ecotone The transition zone between biotic communities in which the typical species of one community intermingle with those of another.
Edaphic factors Having to do with soil.
E horizon A light-colored, eluvial layer that usually occurs between the A and B horizons.
Electromagneticradiation Flow of energy in the form of electromagnetic waves; radiant energy.
Electromagneticspectrum Electromagnetic radiation, arranged according to wavelength.
Elementsofweatherandclimate The basic ingredients of weather and climate—temperature, pressure, wind, and moisture.
Elevation contour line (contour line) A line on a map joining points of equal elevation.
El Niño Periodic atmospheric and oceanic phenomenon of the tropical Pacific that typically involves the weakening or reversal of the trade winds and the warming of surface water off the west coast of South America.
Eluviation The process by which gravitational water picks up fine particles of soil from the upper layers and carries them downward.
Endemic Organism found only in a particular area.
Endothermic [animal] Warm-blooded animal.
Energy The ability to do work; anything that has the ability to change the state or condition of matter.
Enhanced Fujita Scale Classification scale of tornado strength, with EF-0 being the weakest tornadoes and EF-5 being the most powerful.
ENSO (El Niño/Southern Oscillation) Linked atmospheric and oceanic phenomenon of pressure and water temperature. Southern Oscillation refers to a periodic seesaw of atmospheric pressure in the tropical southern Pacific Ocean basin. Also see El Niño.
Entisol The least developed of all soil orders, with little mineral alteration and no pedogenic horizons.
Entrenched meanders A winding, sinuous stream valley with abrupt sides; possible outcome of the rejuvenation of a meandering stream.
Environmental lapse rate The observed vertical temperature gradient of the troposphere.
Ephemeral stream A stream that carries water only during the “wet season” or during and immediately after rains.
Epicenter Location on the surface directly above the center of fault rupture during an earthquake.
Equator The parallel of 0° latitude.
Equilibriumline A theoretical line separating the ablation zone and accumulation zone of a glacier along which accumulation exactly balances ablation.
Equivalent map projection A projection that maintains constant area (size) relationships over the entire map; also called an equal area projection.
Erg “Sea of sand.” A large area covered with loose sand, generally arranged in some sort of dune formation by the wind.
Erosion Detachment, removal and transportation of fragmented rock material.
Esker Long, sinuous ridge of stratified glacial drift composed largely of glaciofluvial gravel and formed by the choking of subglacial streams during a time of glacial stagnation.
Eustatic sea-level change Change in sea level due to an increase or decrease in the amount of water in the world ocean; also known as eustasy.
Evaporation Process by which liquid water is converted to gaseous water vapor; a cooling process because latent heat is stored.
Evapotranspiration The transfer of moisture to the atmosphere by transpiration from plants and evaporation from soil and plants.
Evergreen tree A tree or shrub that sheds its leaves on a sporadic or successive basis but at any given time appears to be fully leaved.
Exfoliation Weathering process in which curved layers peel off bedrock in sheets. This process commonly occurs in granite and related intrusive rocks after overlying rock has been removed, allowing the body to expand slightly. Also referred to as unloading.
Exfoliation dome A large rock mass with a surface configuration that consists of imperfect curves punctuated by several partially fractured shells of the surface layers; result of exfoliation.
Exotic species (exotics) Organisms that are introduced into “new” habitats in which they did not naturally occur.
Exotic stream A stream that flows into a dry region, bringing its water from somewhere else.
External [geomorphic] processes Destructive processes that serve to denude or wear down the landscape. Includes weathering, mass wasting, and erosion.
Extrusive igneous rock Igneous rock formed on the surface of Earth; also called volcanic rock.
Eye (eye of tropical cyclone) The non-stormy center of a tropical cyclone, which has a diameter of 16 to 40 kilometers (10 to 25 miles) and is a singular area of calmness in the maelstrom that whirls around it.
Geography terms and Definitions starting with F | UPSC – IAS
Fall Mass wasting process in which pieces of weathered rock fragments fall to the bottom of a cliff or steep slope; also called rockfall.
Fault A fracture or zone of fracture where the rock structure is forcefully broken and one side is displaced relative to the other. The movement can be horizontal or vertical, or a combination of both.
Fault-block mountain (tilted-fault-block mountain) A mountain formed where a surface block is faulted and relatively upthrown on one side without any faulting or uplift on the other side. The block is tilted asymmetrically, producing a steep slope along the fault scarp and a relatively gentle slope on the other side of the block.
Faultscarp Cliff formed by faulting.
Fauna Related to Animals.
Field capacity The maximum amount of water that can be retained in the soil after the gravitational water has drained away.
Fjord A glacial trough that has been partly drowned by the sea.
Flood basalt A large-scale outpouring of basaltic lava that may cover an extensive area of Earth’s surface.
Floodplain A flattish valley floor covered with stream-deposited sediments (alluvium) and subject to periodic or episodic inundation by overflow from the stream.
Floodtide The movement of ocean water toward the coast in a tidal cycle—from the ocean’s lowest surface level the water rises gradually for about 6 hours and 13 minutes.
Flora Related to Plants.
Fluvial processes Processes involving the work of running water on the surface of Earth.
Foehn a hot southerly wind on the northern slopes of the Alps.(Europe)
Fog A cloud whose base is at or very near ground level.
Folding The bending of crustal rocks by compression and/or uplift.
Food chain Sequential predation in which organisms feed upon one another, with organisms at one level providing food for organisms at the next level, and so on. Energy is thus transferred through the ecosystem.
Food pyramid A conceptualization of energy transfer through the ecosystem from large numbers of “lower” forms of life through succeedingly smaller numbers of “higher” forms, as the organisms at one level are eaten by the organisms at the next higher level. Also see food chain.
Forest An assemblage of trees growing closely together so that their individual leaf canopies generally overlap.
Fractionalscale(fractional map scale) Ratio of distance measured on a map and the actual distance that represents on Earth’s surface, expressed as a ratio or fraction; assumes that the same units of measure are used on the map and on Earth’s surface.
Friction layer Zone of the atmosphere, between Earth’s surface and an altitude of about 1000 meters (3300 feet), where most frictional resistance to air flow is found.
Fringingreef A coral reef built out laterally from the shore, forming a broad bench that is only slightly below sea level, often with the tops of individual coral “heads” exposed to the open air at low tide.
Front A sharp zone of discontinuity between unlike air masses.
Frontal lifting The forced lifting of air along a front.
Frost wedging Fragmentation of rock due to expansion of water that freezes into ice within rock openings.
Fumarole A hydrothermal feature consisting of a surface crack that is directly connected with a deep-seated source of heat. The little water that drains into this tube is instantly converted to steam by heat and gases, and a cloud of steam is then expelled from the opening.
Funnel cloud Funnel-shaped cloud extending down from a cumulonimbus cloud; a tornado is formed when the funnel cloud touches the surface.
Geography terms and Definitions starting with G | UPSC – IAS
Gelisol Soil order that develops in areas of permafrost.
Geographic information systems (GIS) Computerized systems for the capture, storage, retrieval, analysis, and display of spatial (geographic) data.
Geomorphology The study of the characteristics, origin, and development of landforms.
Geostrophicwind A wind that moves parallel to the isobars as a result of the balance between the pressure gradient force and the Coriolis effect.
Geyser A specialized form of intermittent hot spring with water issuing only sporadically as a temporary ejection, in which hot water and steam are spouted upward for some distance.
Glacial erratic Outsize boulder included in the glacial till, which may be very different from the local bedrock.
Glacial flour Rock material that has been ground to the texture of very fine talcum powder by glacial action.
Glacial plucking Action in which rock fragments beneath the ice are loosened and grasped by the freezing of meltwater in joints and fractures, and then pried out and dragged along in the general flow of a glacier. Also called glacial quarrying.
Glacialsteps Series of level or gently sloping bedrock benches alternating with steep drops in the down-valley profile of a glacial trough.
Glacial trough A valley reshaped by an alpine glacier, usually U-shaped.
Glaciofluvialdeposition The action whereby rock debris that is carried along by glaciers is eventually deposited or redeposited by glacial meltwater.
Gleization The dominant pedogenic regime in areas where the soil is saturated with water most of the time due to poor drainage.
Global conveyer-belt circulation Slowly moving circulation of deep ocean water that forms a continuous loop from the North Atlantic to the Antarctic, into the Indian and Pacific Oceans, and back into the North Atlantic.
Global Positioning System (GPS) A satellite-based system for determining accurate positions on or near Earth’s surface.
Globalwarming Popular name given to the recent warming of Earth’s climate due to human-released greenhouse gases.
Graben A block of land bounded by parallel faults in which the block has been downthrown, producing a distinctive structural valley with a straight, steep-sided fault scarp on either side.
Gradient Elevation change of a stream over a given distance.
Granite The most common and well-known plutonic (intrusive) rock; coarse-grained rock consisting of both dark- and light-colored minerals; forms from felsic (relatively high silica content) magma.
Graphicscale (graphic map scale) The use of a line marked off in graduated distances as a map scale.
Grassland Plant association dominated by grasses and forbs.
Great circle Circle on a globe formed by the intersection of Earth’s surface with any plane that passes through Earth’s center.
Greenhouse effect The warming in the lower troposphere because of differential transmissivity for shortwave and longwave radiation through the greenhouse gases in the atmosphere; the atmosphere easily transmits shortwave radiation from the Sun but inhibits the transmission of longwave radiation from the surface.
Greenhouse gases Gases with the ability to transmit incoming shortwave radiation from the Sun but absorb outgoing longwave terrestrial radiation. The most important natural greenhouse gases are water vapor and carbon dioxide.
Greenwich Mean Time (GMT) Time in the Greenwich time zone. Today more commonly called UTC or Universal Time Coordinated
Groin A short wall built perpendicularly from the beach into the shore zone to interrupt the longshore current and trap sand.
Groundmoraine A moraine consisting of glacial till deposited widely over a land surface beneath an ice sheet.
Groundwater Water found underground in the zone of saturation.
Gymnosperms Seed re-producing plants that carry their seeds in cones; “naked seeds.”
Geography terms and Definitions starting with H | UPSC – IAS
Hadley cells Two complete vertical convective circulation cells between the equator, where warm air rises in the ITCZ, and 25° to 30° of latitude, where much of the air subsides into the subtropical highs.
Hail Rounded or irregular pellets or lumps of ice produced in cumulonimbus clouds as a result of active turbulence and vertical air currents. Small ice particles grow by collecting moisture from supercooled cloud droplets.
Hamada A barren desert surface of consolidated material that usually consists of exposed bedrock but is sometimes composed of sedimentary material that has been cemented together by salts evaporated from groundwater.
Hanging valley (hanging trough) A tributary glacial trough, the bottom of which is considerably higher than the bottom of the principal trough that it joins.
Headwarderosion Erosion that cuts into the interfluve at the upper end of a gully or valley.
Heat Energy that transfers from one object or substance to another because of a difference in temperature. Sometimes the term thermal energy is used interchangeably with the term heat.
High [pressure cell] Area of relatively high atmospheric pressure.
Highland climate High mountain climate where altitude is dominant control. Designated H in Köppen system.
Highland ice field Largely unconfined ice sheet in high mountain area.
Histosol A soil order characterized by organic, rather than mineral, soils, which is invariably saturated with water all or most of the time.
Horizon (soil horizon) The more or less distinctly recognizable layer of soil, distinguished from one another by differing characteristics and forming a vertical zonation of the soil.
Horn A steep-sided, pyramidal rock pinnacle formed by expansive glacial plucking and frost wedging of the headwalls where three or more cirques intersect.
Horse latitudes Areas in the subtropical highs characterized by warm sunshine and an absence of wind.
Horst A relatively uplifted block of land between two parallel faults.
Hot spot An area of volcanic activity within the interior of a lithospheric plate associated with magma rising up from the mantle below.
Hot spring Hot water at Earth’s surface that has been forced upward through fissures or cracks by the pressures that develop when underground water has come in contact with heated rocks or magma beneath the surface.
Humid continentalclimate Severe mid-latitude climate characterized by hot summers, cold winters, and precipitation throughout the year.
Humid subtropicalclimate Mild mid-latitude climate characterized by hot summers and precipitation throughout the year.
Humus A dark-colored, gelatinous, chemically stable fraction of organic matter on or in the soil.
Hurricane A tropical cyclone with wind speeds of 119 km/hr (74 mph; 64 knots) or greater affecting North or Central America.
Hydrogenbond Attraction between water molecules in which the negatively charged oxygen side of one water molecule is attracted to the positively charged hydrogen side of another water molecule.
Hydrologiccycle A series of storage areas interconnected by various transfer processes, in which there is a ceaseless interchange of moisture in terms of its geographical location and its physical state.
Hydrolysis A chemical union of water with another substance to produce a new compound that is nearly always softer and weaker than the original.
Hydrophytic adaptations Terrestrial plants adapted to living in very wet environments.
Hydrosphere Total water realm of Earth, including the oceans, surface waters of the lands, groundwater, and water held in the atmosphere.
Hydrothermalactivity The outpouring or ejection of hot water, often accompanied by steam, which usually takes the form of either a hot spring or a geyser.
Hydrothermalmetamorphism Metamorphism associated with hot, mineral-rich solutions circulating around preexisting rock.
Geography terms and Definitions starting with I | UPSC – IAS
Iceberg A great chunk of floating ice that breaks off an ice shelf or the end of an outlet glacier.
Ice cap climate Polar climate characterized by temperatures below freezing throughout the year.
Ice floe A mass of ice that breaks off from larger ice bodies (ice sheets, glaciers, ice packs, and ice shelves) and floats independently in the sea. This term is generally used with large, flattish, tabular masses.
Ice pack The extensive and cohesive mass of floating ice that is found in the Arctic and Antarctic oceans.
Ice shelf A massive portion of an ice sheet that projects out over the sea.
Igneous intrusion Features formed by the emplacement and cooling of magma below the surface.
Igneous rock Rock formed by solidification of molten magma.
Illuviation The process by which fine particles of soil from the upper layers are deposited at a lower level.
Inceptisol An immature order of soils that has relatively faint characteristics; not yet prominent enough to produce diagnostic horizons.
Inclination [of Earth’s axis] The tilt of Earth’s rotational axis relative to its orbital plane (the plane of the ecliptic).
Infrared [radiation] Electromagnetic radiation in the wavelength range of about 0.7 to 1000 micrometers; wavelengths just longer than visible light.
Inner core The solid, dense, innermost portion of Earth, believed to consist largely of iron and nickel.
Inselberg “Island mountain”; isolated summit rising abruptly from a low-relief surface.
Insolation Incoming solar radiation.
Interfluve The higher land or ridge above the valley sides that separates adjacent valleys; drained by overland flow.
Intermittentstream A stream that carries water only part of the time, during the “wet season” or during and immediately after rains.
Internal [geomorphic] processes Geomorphic processes originating below the surface; include volcanism, folding, and faulting.
InternationalDateLine The line marking a time difference of an entire day from one side of the line to the other. Generally, this line falls on the 180th meridian except where it deviates to avoid separating an island group.
International System of measurement (SI) Popularly known as the “metric system” of measurement.
Intertropical convergence zone (ITCZ) The region near or on the equator where the northeast trades and the southeast trades converge; associated with rising air of the Hadley cells and frequent thunderstorms.
Intrusive igneous rock Igneous rock formed below ground from the cooling and solidification of magma; also called plutonic rock.
Invertebrates Animals without backbones.
Isobar A line joining points of equal atmospheric pressure.
Isohyet A line joining points of equal numerical value of precipitation.
Isoline A line on a map connecting points that have the same quality or intensity of a given phenomenon.
Isostasy Maintenance of the hydrostatic equilibrium of Earth’s crust; the sinking of the crust as weight is applied and the rising of crust as weight is removed.
Isotherm A line joining points of equal temperature.
ITCZ The Inter Tropical Convergence Zone, or ITCZ, is a belt of low pressure which circles the Earth generally near the equator where the trade winds of the Northern and Southern Hemispheres come together. It is characterised by convective activity which generates often vigorous thunderstorms over large areas.
Geography terms and Definitions starting with J | UPSC – IAS
Jet stream A rapidly moving current of wind in the upper troposphere; jet streams can be thought of as the high-speed “cores” of the high altitude westerly wind flow that frequently meander in a north-south direction over the midlatitudes.
Jetty A wall built into the ocean at the entrance of a river or harbor to protect against sediment deposition, storm waves, and currents.
Joints Cracks that develop in bedrock due to stress, but in which there is no appreciable movement parallel to the walls of the joint.
June solstice Day of the year when the vertical rays of the Sun strike the Tropic of Cancer; on or about June 21; summer solstice in the Northern Hemisphere.
Geography terms and Definitions starting with K | UPSC – IAS
karst Topography developed as a consequence of subsurface solution.
katabatic wind A wind that originates in cold upland areas and cascades toward lower elevations under the influence of gravity.
kettle An irregular depression in a morainal surface created when blocks of stagnant ice eventually melt.
kinetic energy The energy of movement.
knickpoint A sharp irregularity (such as a waterfall, rapid, or cascade) in a stream-channel profile; also known as a nickpoint.
knickpointmigration Upstream shift in location of a knickpoint due to erosion.
Köppen climate classification system A climatic classification of the world devised by Wladimir Köppen.
Geography terms and Definitions starting with L | UPSC – IAS
lagoon A body of quiet salt or brackish water in an area between a barrier island or a barrier reef and the mainland.
lahar Volcanic mudflow; a fast-moving muddy flow of volcanic ash and rock fragments.
lake A lake is an area filled with water, localized in a basin, that is surrounded by land, apart from any river or other outlet that serves to feed or drain the lake.
land breeze Local wind blowing from land to water, usually at night. landform An individual topographic feature, of any size; the term landforms refers to topography.
landslide An abrupt and often catastrophic event in which a large mass of rock and/or soil slides bodily downslope in only a few seconds or minutes. An instantaneous collapse of a slope.
La Niña Atmospheric and oceanic phenomenon associated with cooler than usual water off the west coast of South America. Sometimes described as the opposite of El Niño.
large-scale map A map with a scale that is a relatively large representative fraction and therefore portrays only a small portion of Earth’s surface, but in considerable detail.
latent heat Energy stored or released when a substance changes state. For example, evaporation is a cooling process because latent heat is stored and condensation is a warming process because latent heat is released.
latent heat of condensation Heat released when water vapor condenses back to liquid form.
latent heat of evaporation Energy stored when liquid water evaporates to form water vapor.
lateral erosion Erosion that occurs when the principal current of a stream swings laterally from one bank to the other, eroding where the velocity is greatest on the outside bank and depositing alluvium where it is least on the inside bank.
lateral moraine Well-defined ridge of unsorted debris (till) built up along the sides of valley glaciers, parallel to the valley walls.
laterization The dominant pedogenic regime in areas where temperatures are relatively high throughout the year and which is characterized by rapid weathering of parent material, dissolution of nearly all minerals, and the speedy decomposition of organic matter.
latitude Location described as an angle measured north and south of the equator.
lava Molten magma that is extruded onto the surface of Earth, where it cools and solidifies.
lavadome(plug dome) Dome or bulge formed by the pushing up of viscous magma in a volcanic vent.
leaching Process in which dissolved nutrients are transported down in solution and deposited deeper in a soil.
lifting condensation level (LCL) The altitude at which rising air cools sufficiently to reach 100 percent relative humidity at the dew point temperature, and condensation begins.
lightning A luminous electric discharge in the atmosphere caused by the separation of positive and negative charges associated with cumulonimbus clouds.
limitingfactor Variable that is important or most important in determining the survival of an organism.
linear fault trough Straight-line valley that marks the surface position of a fault, especially a strike-slip fault; formed by the erosion or settling of crushed rock along the trace of a fault.
liquefaction Phenomenon observed during an earthquake when water saturated soil or sediments become soft or even fluid during the time of strong ground shaking.
lithosphere Tectonic plates consisting of the crust and upper rigid mantle. Also used as a general term for the entire solid Earth (one of the Earth “spheres”).
litter The collection of dead plant parts that accumulate at the surface of the soil.
loam A soil texture in which none of the three principal soil separates – sand, silt, and clay – dominates the other two.
loess A fine-grained, wind-deposited silt. Loess lacks horizontal stratification, and its most distinctive characteristic is its ability to stand in vertical cliffs.
longitude Location described as an angle measured (in degrees, minutes, and seconds) east and west from the prime meridian on Earth’s surface.
longshorecurrent A current in which water moves roughly parallel to the shoreline in a generally downwind direction; also called a littoral current.
longwave radiation Wavelengths of thermal infrared radiation emitted by Earth and the atmosphere; also referred to as terrestrial radiation.
low [pressure cell] Area of relatively low atmospheric pressure.
loxodrome (rhumb line) A true compass heading; a line of constant compass direction.
Geography terms and Definitions starting with M | UPSC – IAS
Magma Molten material below Earth’s surface.
Magnitude [of an earthquake] Scale used to describe the relative amount of energy released during an earthquake. Several different magnitude scales are in current use, such as the moment magnitude and the Richter scale.
Mantle The portion of Earth beneath the crust and surrounding the core.
Mantle plume A plume of mantle magma that rises to, or almost to, Earth’s surface; not directly associated with most lithospheric plate boundaries, but associated with many hot spots.
Map A flat representation of Earth at a reduced scale, showing only selected detail.
Map projection A systematic representation of all or part of the three dimensional Earth surface on a two-dimensional flat surface. map scale Relationship between distance measured on a map and the actual distance on Earth’s surface.
March equinox One of two days of the year when the vertical rays of the Sun strike the equator; every location on Earth has equal day and night; occurs on or about March 20 each year.
Marine west coast climate Mild mid-latitude climate characterized by mild temperatures and precipitation throughout the year.
Marine terrace A platform formed by marine erosion that has been uplifted above sea level.
Marsh Flattish surface area that is submerged in water at least part of the time but is shallow enough to permit the growth of water-tolerant plants, primarily grasses and sedges.
Masswasting The short-distance downslope movement of weathered rock under the direct influence of gravity; also called mass movement.
Master joints Major joints that run for great distances through a bedrock structure.
Meander scar A dry former stream channel meander through which the stream no longer flows.
Mechanicalweathering The physical disintegration of rock material without any change in its chemical composition; also called physical weathering.
Medialmoraine A dark band of rocky debris down the middle of a glacier created by the union of the lateral moraines of two adjacent glaciers.
Mediterranean climate Mild mid-latitude climate characterized by dry summers and wet winters.
Mediterranean woodland and shrub Woodland and shrub plant association found in regions of mediterranean climate.
Mercator projection A cylindrical projection mathematically adjusted to attain complete conformality which has a rapidly increasing scale with increasing latitude; straight lines on a Mercator projection are lines of constant compass heading (loxodromes).
Meridian An imaginary line of longitude extending from pole to pole, crossing all parallels at right angles, and being aligned in true north– south directions.
Mesa A flat-topped, steep-sided hill with a limited summit area.
Mesocyclone Cyclonic circulation of air within a severe thunderstorm; diameter of about 10 kilometers (6 miles).
Metamorphic rock Rock that was originally something else but has been drastically changed by massive forces of heat, pressure, and/or hydrothermal fluids working on it from within Earth.
Mid-latitude anticyclone An extensive migratory high-pressure cell of the midlatitudes that moves generally with the westerlies.
Mid-latitude cyclone Large migratory low-pressure system that occurs within the midlatitudes and moves generally with the westerlies. Also called extratropical cyclone and wave cyclone.
Mid-latitude desert climate Desert climate characterized by warm summers but cold winters.
Mid-latitude grassland Grassland plant assemblage in semiarid regions of the midlatitudes; regionally called steppe, prairie, pampa, and veldt.
Mid-ocean ridge A lengthy system of deep-sea mountain ranges, generally located at some distance from any continent; formed by divergent plate boundaries on the ocean floor.
Milankovitch cycles Combination of long-term astronomical cycles involving Earth’s inclination, precession, and eccentricity of orbit; believed at least partially responsible for major periods of glaciation and deglaciation. Named for Milutin Milankovitch, an early twentieth- century Yugoslavian astronomer, who studied these cycles.
Millibar A measure of pressure, consisting of one-thousandth part of a bar, or 1000 dynes per square centimeter (1 dyne is the force needed to accelerate 1 gram of mass 1 centimeter per second per second).
Mineral A naturally formed solid inorganic substance that has a specified chemical composition and crystal structure.
Modified Mercalli intensity scale Qualitative scale from I to XII used to describe the relative strength of ground shaking during an earthquake.
Mohorovicˇic´ discontinuity The boundary between Earth’s crust and mantle. Also known simply as the Moho.
Mollisol A soil order characterized by the presence of a mollic epipedon, which is a mineral surface horizon that is dark, thick, contains abundant humus and base nutrients, and retains a soft character when it dries out.
Monsoon A seasonal reversal of winds; a general onshore movement in summer and a general offshore flow in winter, with a very distinctive seasonal precipitation regime.
Moraine The largest and generally most conspicuous landform feature produced by glacial deposition of till, which consists of irregular rolling topography that rises somewhat above the level of the surrounding terrain.
Mountain breeze Downslope breeze from a mountain due to chilling of air on its slopes at night.
Mudflow Rapid, downslope movement of a dense mixture of weathered rock and water through or within a valley.
Multispectral [remote sensing] A remote sensing instrument that collects multiple digital images simultaneously in different electromagnetic wavelength bands.
Geography terms and Definitions starting with N | UPSC – IAS
Natural levee An embankment of slightly higher ground fringing a stream channel in a floodplain; formed by deposition during flood-time.
Neap tides The lower-than-normal tidal variations that occur twice a month as the result of the alignment of the Sun and Moon at a right angle to one another.
Needleleaf trees Trees adorned with thin slivers of tough, leathery, waxy needles rather than typical leaves.
Net primary productivity The net photosynthesis of a plant community over a period of one year, usually measured in the amount of fixed carbon per unit area (kilograms of carbon per square meter per year).
Névé Snow granules that have become packed and begin to coalesce due to compression, achieving a density about half as great as that of water; also called firn.
Nitrogen cycle An endless series of processes in which nitrogen moves through the environment.
Nitrogen fixation Conversion of gaseous nitrogen into forms that can be used by plant life.
Normal fault The result of tension (extension) producing a steeply inclined fault plane, with the block of land on one side being pushed up, or upthrown, in relation to the block on the other side, which is downthrown.
North Pole Latitude of 90° north.
Geography terms and Definitions starting with O | UPSC – IAS
Occluded front A complex front formed when a cold front overtakes a warm front, lifting all of the warm air mass off the ground.
Occlusion Process of cold front overtaking a warm front to form an occluded front.
Ocean floor core samples Rock and sediment samples removed from ocean floor.
Oceanic trench (deep oceanic trench) Deep linear depression in the ocean floor where subduction is taking place.
Offset stream A stream course displaced by lateral movement along a fault.
O horizon The immediate surface layer of a soil profile, consisting mostly of organic material.
Orographic lifting Uplift that occurs when air is forced to rise over topographic barriers.
Outcrop Surface exposure of bedrock.
Outer core The liquid (molten) shell beneath the mantle that encloses Earth’s inner core.
Outwash plain Extensive glaciofluvial feature that is a relatively smooth, flattish alluvial apron deposited beyond recessional or terminal moraines by streams issuing from ice.
Overland flow The general movement of unchanneled surface water down the slope of the land surface.
Oxbow lake A cutoff meander that initially holds water.
Oxidation The chemical union of oxygen atoms with atoms from various metallic elements to form new products, which are usually more voluminous, softer, and more easily eroded than the original compounds.
Oxisol The most thoroughly weathered and leached of all soils. This soil order invariably displays a high degree of mineral alteration and profile development.
Oxygencycle The movement of oxygen by various processes through the environment.
Oxygen isotopeanalysis Using the ratio of 16O (oxygen 16) and 18O (oxygen 18) isotopes in compounds such as water and calcium carbonate to infer temperature and other conditions in the past.
Ozone A gas composed of molecules consisting of three atoms of oxygen, O3.
Ozone layer The layer in the atmosphere between 16 and 40 kilometers (10 and 25 miles) high, where the concentration of ozone is greatest; the ozone layer absorbs much of the incoming ultraviolet solar radiation.
Geography terms and Definitions starting with P | UPSC – IAS
Pacific ring of fire Name given to the rim of the Pacific Ocean basin due to widespread volcanic and seismic activity; associated with lithospheric plate boundaries.
Paleoclimatology The study of past climates.
Paleomagnetism Past magnetic orientation.
Pangaea The massive supercontinent that Alfred Wegener first postulated to have existed about 200 million years ago. Pangaea broke apart into several large sections that have continually moved away from one another and that now comprise the present continents.
Parallel A line connecting all points of equal latitude; such a line is parallel to all other parallels.
Parallelism – The polarity of the Earth’s magnetic field is recorded in igneous rocks, and reversals of the field are thus detectable as “stripes” centered on mid-ocean ridges where the sea floor is spreading, while the stability of the geomagnetic poles between reversals has allowed paleomagnetists to track the past motion of continents.
Parent material The source of the weathered fragments of rock from which soil is made; solid bedrock or loose sediments that have been transported from elsewhere by the action of water, wind, or ice.
Particulate Composed of distinct tiny particles or droplets suspended in the atmosphere; also known as aerosols.
Paternoster lakes A sequence of small lakes found in the shallow excavated depressions or steps within a glacial trough.
Patterned ground Polygonal patterns in the ground that develop in areas of seasonally frozen soil and permafrost.
Pediment A gently inclined bedrock platform that extends outward from a mountain front, usually in an arid region.
Pedogenicregimes Soil-forming regimes that can be thought of as environmental settings in which certain physical/chemical/biological processes prevail.
Ped A larger mass or clump that individual soil particles tend to aggregate into and that determines the structure of the soil.
Perennial plants (perennials) Plants that can live more than a single year despite seasonal environmental variations.
Perennial stream A permanent stream that contains water the year round.
Periglacial zone An area of indefinite size beyond the outermost extent of ice advance that was indirectly influenced by glaciation.
Perihelion The point in its orbit where Earth is nearest to the Sun (about 147,100,000 kilometers or 91,400,000 miles).
Permafrost Permanent ground ice or permanently frozen subsoil.
Permeability A soil or rock characteristic in which there are interconnected pore spaces through which water can move.
Photochemical smog Form of secondary air pollution caused by the reaction of nitrogen compounds and hydrocarbons to ultraviolet radiation in strong sunlight.
Photoperiodism The response of an organism to the length of exposure to light in a 24-hour period.
Photosynthesis The basic process whereby plants produce stored chemical energy from water and carbon dioxide and which is activated By sunlight.
Physical geography Study of the physical elements of geography.
Piedmontzone Zone at the “foot of the mountains.”
Piezometric surface The elevation to which groundwater will rise under natural confining pressure in a well.
Pinnacle An erosional remnant in the form of a steep-sided spire that has a resistant caprock; normally found in an arid or semiarid environment; also speleothem column.
Planar projection (plane projection) A family of maps derived by the perspective extension of the geographic grid from a globe to a plane that is tangent to the globe at some point.
Plane of the ecliptic The imaginary plane that passes through the Sun and through Earth at every position in its orbit around the Sun; the orbital plane of Earth.
Plant respiration Stored energy in carbohydrates consumed directly by the plant itself; carbohydrates are oxidized, releasing water, carbon dioxide, and heat energy.
Plant succession The process whereby one type of vegetation is replaced naturally by another.
plastic flow [of glacial ice] Slow, non-brittle flow and movement of ice under pressure.
Plateau Flattish erosional platform bounded on at least one side by a prominent escarpment.
Plate tectonics A coherent theory of massive lithospheric rearrangement based on the movement of continent-sized plates.
Playa Dry lake bed in a basin of interior drainage.
PleistoceneEpoch An epoch of the Cenozoic era between the Pliocene and the Holocene; from about 2.6 million to about 11,700 years ago.
Pleistocenelakes Large freshwater lakes that formed in basins of interior drainage because of higher rainfall and/or lower evaporation during the Pleistocene.
Plugdome Volcano dome or bulge formed by the pushing up of viscous magma in a volcanic vent; also lava dome.
Pluton A large, intrusive igneous body.
Plutonic rock Igneous rock formed below ground from the cooling and solidification of magma; also called intrusive rock.
Pluvial (pluvial effects) Pertaining to rain; often used in connection with a past rainy period.
Podzolization The dominant pedogenic regime in areas where winters are long and cold, and which is characterized by slow chemical weathering of soils and rapid mechanical weathering from frost action, resulting in soils that are shallow, acidic, and with a fairly distinctive profile.
Polar easterlies A global wind system that occupies most of the area between the polar highs and about 60° of latitude. The winds move generally from east to west and are typically cold and dry.
Polar front The contact between unlike air masses in the subpolar low-pressure zone at about 60º N and S.
Polar high A high-pressure cell situated over either polar region.
Polarity [of Earth’s rotation axis] A characteristic of Earth’s axis wherein it always points toward Polaris (the North Star) at every position in Earth’s orbit around the Sun. Also called parallelism.
Porosity The amount of pore space between the soil particles and between the peds, which is a measure of the capacity of the soil to hold water and air.
Precipitation Drops of liquid or solid water falling from clouds.
Precipitation variability Expected departure from average annual precipitation in any given year.
Pressure gradient Change in atmospheric pressure over some horizontal distance.
Primary consumer Animals that eat plants as the first stage in a food pyramid or chain.
Primary pollutants Contaminants released directly into the air.
Prime meridian The meridian passing through the Royal Observatory at Greenwich (England), just east of central London, and from which longitude is measured.
Producers Organisms that produce their own food through photosynthesis; plants.
Proglacial lake A lake formed when ice flows across or against the general slope of the land and the natural drainage is impeded or completely blocked so that meltwater from the ice becomes impounded against the ice front.
Pseudocylindrical projection (elliptical projection) A family of map projections in which the entire world is displayed in an oval shape.
Pyroclastic flow High-speed avalanche of hot gases, ash, and rock fragments emitted from a volcano during an explosive eruption; also known as a nuée ardente.
Pyroclastics (pyroclastic material) Solid rock fragments thrown into the air by volcanic explosions.
Geography terms and Definitions starting with R | UPSC – IAS
Radiant energy It is the energy of electromagnetic waves. The term is most commonly used in the fields of radiometry, solar energy, heating and lighting, but is also used less frequently in other fields (such as telecommunications). radiant energy is the energy of electromagnetic and gravitational radiation. As energy, its SI unit is the joule. The quantity of radiant energy may be calculated by integrating radiant flux with respect to time
Radiation The process in which electromagnetic energy is emitted from a body; the flow of energy in the form of electromagnetic waves.
Rain The most common and widespread form of precipitation, consisting of drops of liquid water.
Rain shadow Area of low rainfall on the leeward side of a mountain range or topographic barrier.
Recessional moraine A glacial deposit of till formed during a pause in the retreat of the ice margin.
Recurrence interval [of a flood] The probability of a given-size flood occurring in a year; also called the return period.
Reflection The ability of an object to repel waves without altering either the object or the waves.
Reg A desert surface of coarse material from which all sand and dust have been removed by wind and water erosion. Often referred to as desert pavement or desert armor.
Regional metamorphism Widespread subsurface metamorphism of rock as a result of prolonged exposure to heat and high pressure, such as in areas of plate collision or subduction.
Regolith A layer of broken and partly decomposed rock particles that covers bedrock.
Relativehumidity An expression of the amount of water vapor in the air (the water vapor content) in comparison with the maximum amount that could be there if the air were saturated (the capacity). This is a ratio that is expressed as a percentage.
Relief The difference in elevation between the highest and lowest points in an area; the vertical variation from mountaintop to valley bottom.
Remote sensing Measurement or acquisition of information by a recording device that is not in physical contact with the object under study; instruments used commonly include cameras and satellites.
Reverse fault A fault produced from compression, with the upthrown block rising steeply above the downthrown block.
Revolution [around the Sun] The orbital movement of Earth around the Sun over the year.
R horizon The consolidated bedrock at the base of a soil profile.
Ria shoreline An embayed coast with numerous estuaries; formed by the flooding of stream valleys by the sea.
Ridge [of atmospheric pressure] Linear or elongated area of relatively high atmospheric pressure.
Riparianvegetation Streamside growth, particularly prominent in relatively dry regions, where stream courses may be lined with trees, although no other trees are to be found in the landscape.
Roche moutonnée A characteristic glacial landform produced when a bedrock hill or knob is overridden by moving ice. The stoss side is smoothly rounded and streamlined by grinding abrasion as the ice rides up the slope, but the lee side is shaped largely by plucking, which produces a steeper and more irregular slope.
Rock Solid material composed of aggregated mineral material.
Rock cycle Term given to the long-term “recycling” of mineral material from one kind of rock to another.
Rockfall (fall) Mass wasting process in which weathered rock drops to the foot of a cliff or steep slope.
Rock glacier An accumulated talus mass that moves slowly but distinctly downslope under its own weight.
Rossbywave A very large north–south undulation of the upper-air westerlies and jet stream.
Rotation [of Earth] The spinning of Earth around its imaginary north– south axis.
Runoff Flow of water from land to oceans by overland flow, streamflow, and groundwater flow.
Geography terms and Definitions starting with S | UPSC – IAS
Saffir-Simpson Hurricane Scale Classification system of hurricane strength with category 1 the weakest and category 5 the strongest.
Sagpond A pond caused by the collection of water from springs and/or runoff into sunken ground, resulting from the crushing of rock in an area of fault movement.
Salina Dry lake bed that contains an unusually heavy concentration of salt in the lake-bed sediment.
Salinelake Salt lake; commonly caused by interior stream drainage in an arid environment.
Salinity A measure of the concentration of dissolved salts.
Salinization One of the dominant pedogenic regimes in areas where principal
Soil moisture movement is upward because of a moisture deficit.
Salt wedging Rock disintegration caused by the crystallization of salts from evaporating water.
Sand dune A mound, ridge, or low hill of loose, windblown sand.
Santa Ana winds Name given to dry, usually warm, and often very strong winds blowing offshore in southern California region.
Saturated adiabatic rate (saturated adiabatic lapse rate) The diminished rate of cooling, averaging about 6°C per 1000 meters (3.3°F per 1000 feet) of rising air above the lifting condensation level; a result of the latent heat of condensation counteracting some of the adiabatic cooling of rising air.
Saturation vapor pressure The maximum pressure that can be exerted by water vapor at a given temperature; the pressure exerted by water vapor when the air is saturated.
Scattering The deflection of light waves in random directions by gas molecules and particulates in the atmosphere; shorter wavelengths of visible light are more easily scattered than longer wavelengths.
Scree Pieces of weathered rock, especially small pieces, that fall directly downslope; also called talus.
Sea breeze A wind that blows from the sea toward the land, usually during the day.
Seafloor spreading The pulling apart of lithospheric plates to permit the rise of deep-seated magma to Earth’s surface in midocean ridges.
Secondary consumer Animals that eat other animals, as the second and further stages in a food pyramid or chain.
Secondary pollutant Pollutants formed in the atmosphere as a consequence of chemical reactions or other processes; for example see photochemical smog.
Sediment Small particles of rock debris or organic material deposited by water, wind, or ice.
Sediment budget [of a beach] The balance between the sediment being deposited on a beach and the sediment that is being transported away from a beach.
Sedimentary rock Rock formed of sediment that is consolidated by the combination of pressure and cementation.
Seif (longitudinal) dune Long, narrow desert dunes that usually occur in multiplicity and in parallel arrangement.
Sensible temperature The relative apparent temperature that is sensed by a person’s body.
Separates The size groups within the standard classification of soil particle sizes.
September equinox One of two days of the year when the vertical rays of the Sun strike the equator; every location on Earth has equal day and night; occurs on or about September 22 each year.
Shield volcanoes Volcanoes built up in a lengthy outpouring of very fluid basaltic lava. Shield volcanoes are broad mountains with gentle slopes.
Shortwave radiation Wavelengths of radiation emitted by the Sun, especially ultraviolet, visible, and short infrared radiation.
Shrubland Plant association dominated by relatively short woody plants.
Silicate mineral (silicates) A category of minerals composed of silicon and oxygen combined with another element or elements.
Sinkhole (doline) A small, rounded depression that is formed by the dissolution of surface limestone, typically at joint intersections.
Slip face [of sand dune] Steeper leeward side of a sand dune.
Slump A slope collapse slide with rotation along a curved sliding plane.
Small-scale map A map whose scale is a relatively small representative fraction and therefore shows a large portion of Earth’s surface in limited detail.
Snow Solid precipitation in the form of ice crystals, small pellets, or flakes, which is formed by the direct conversion of water vapor into ice.
Soil An infinitely varying mixture of weathered mineral particles, decaying organic matter, living organisms, gases, and liquid solutions. Soil is that part of the outer “skin” of Earth occupied by plant roots.
Soil order The highest (most general) level of soil classification in the Soil Taxonomy.
Soil profile A vertical cross section from Earth’s surface down through the soil layers into the parent material beneath.
Soil Taxonomy The system of soil classification currently in use in the United States. It is genetic in nature and focuses on the existing properties of the soil rather than on environment, genesis, or the properties it would possess under virgin conditions.
Soil–water balance The relationship between gain, loss, and storage of soil water.
Soil–water budget An accounting that demonstrates the variation of the soil–water balance over a period of time.
Solar altitude Angle of the Sun above the horizon.
Solifluction A special form of soil creep in tundra areas; associated with summer thawing of the near-surface portion of permafrost, causing the wet, heavy surface material to sag slowly downslope.
Solum The true soil that includes only the top four horizons: O, the organic surface layer; A, the topsoil; E, the eluvial layer; and B, the subsoil.
Southern Oscillation Periodic “seesaw” of high and low atmospheric pressure between northern Australia and Tahiti; first recognized by Gilbert Walking in the early twentieth century.
Specificheat The amount of energy required to raise the temperature of 1 gram of a substance by 1°C. Also called specific heat capacity.
Specific humidity A direct measure of water-vapor content expressed as the mass of water vapor in a given mass of air (grams of vapor/ kilograms of air).
Speleothem A feature formed by precipitated deposits of minerals on the wall, floor, or roof of a cave.
Spit A linear deposit of marine sediment that is attached to the land at one or both ends.
Spodosol A soil order characterized by the occurrence of a spodic subsurface horizon, which is an illuvial layer where organic matter and aluminum accumulate, and which has a dark, sometimes reddish, color.
Spring tide A time of maximum tide that occurs as a result of the alignment of Sun, Moon, and Earth.
Stable [air] Air that rises only if forced.
Stalactite A pendant structure hanging downward from a cavern’s roof.
Stalagmite A projecting structure growing upward from a cavern’s floor.
Star dune Pyramid-shaped sand dune with arms radiating out in three or more directions.
Stationaryfront The common boundary between two air masses in a situation in which neither air mass displaces the other.
Storm surge A surge of wind-driven water as much as 8 meters (25 feet) above normal tide level, which occurs when a hurricane advances onto a shoreline.
Storm warning Weather advisory issued when a severe thunderstorm or tornado has been observed in an area; people should seek safety immediately.
Storm watch Weather advisory issued when conditions are favorable for strong thunderstorms or tornadoes.
Strata Distinct layers of sediment or layers in sedimentary rock.
Stratified drift Drift that was sorted as it was carried along by the flowing glacial meltwater.
Stratosphere Atmospheric layer directly above the troposphere.
Stratus clouds Layered, horizontal clouds, often below altitudes of 2 kilometers (6500 feet), which sometimes occur as individual clouds but more often appear as a general overcast.
Stream Channeled flow of water, regardless of size.
Stream capacity The maximum load that a stream can transport under given conditions.
Stream capture (stream piracy) An event where a portion of the flow of one stream is diverted into that of another by natural processes.
Stream competence The size of the largest particle that can be transported by a stream.
Streamflow Channeled movement of water along a valley bottom.
Stream load Solid matter carried by a stream.
Stream order Concept that describes the hierarchy of a drainage network.
Stream rejuvenation When a stream gains downcutting ability, usually through regional tectonic uplift.
Stream terrace Remnant of a previous valley floodplain of a rejuvenated stream.
Strike-slip fault A fault produced by shearing, with adjacent blocks being displaced laterally with respect to one another. The movement is mostly or entirely horizontal.
Subarctic climate Severe mid-latitude climate found in high latitude continental interiors, characterized by very cold winters and an extreme annual temperature range.
Subduction Descent of the edge of an oceanic lithospheric plate under the edge of an adjoining plate.
Sublimation The process by which water vapor is converted directly to ice, or vice versa.
Subpolarlow A zone of low pressure that is situated at about 50° to 60° of latitude in both Northern and Southern Hemispheres (also referred to as the polar front).
Subtropical gyres The closed-loop pattern of surface ocean currents around the margins of the major ocean basins; the flow is clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.
Subtropical desertclimate A hot desert climate; generally found in subtropical latitudes, especially on the western sides of continents.
Subtropical high (STH) Large, semipermanent, high-pressure cells centered at about 30° N and S over the oceans, which have average diameters of 3200 kilometers (2000 miles) and are usually elongated east–west.
Supersaturated [air] Air in which the relative humidity is greater than 100 percent but condensation is not taking place.
Surface tension Because of electrical polarity, liquid water molecules tend to stick together—a thin “skin” of molecules forms on the surface of liquid water causing it to “bead.”
Suspended load The very fine particles of clay and silt that are in suspension and move along with the flow of water without ever touching the streambed.
Swallowhole The distinct opening at the bottom of some sinkholes through which surface drainage can pour directly into an underground channel.
Swamp A flattish surface area that is submerged in water at least part of the time but is shallow enough to permit the growth of water-tolerant plants—predominantly trees.
Swash The cascading forward motion of a breaking wave that rushes up the beach.
Swell An ocean wave, usually produced by stormy conditions, that can travel enormous distances away from the source of the disturbance.
Symbiosis A mutually beneficial relationship between two organisms.
Syncline A simple downfold in the rock structure.
Geography terms and Definitions starting with U | UPSC – IAS
Ubac slope A slope oriented so that sunlight strikes it at a low angle and hence is much less effective in heating and evaporating than on the adret slope, thus producing more luxuriant vegetation of a richer diversity.
Ultisol A soil order similar to Alfisols, but more thoroughly weathered and more completely leached of bases.
Ultraviolet (UV) radiation Electromagnetic radiation in the wavelength range of 0.1 to 0.4 micrometers.
Uniformitarianism The concept that the “present is the key to the past” in geomorphic processes. The processes now operating have also operated in the past.
Universal Time Coordinated (UTC) or Coordinated Universal Time The world time standard reference; previously known as Greenwich mean time (GMT).
Unstable [air] Air that rises without being forced.
Upwelling Cold, deep ocean water that rises to the surface where wind patterns deflect surface water away from the coast; especially common along the west coasts of continents in the subtropics and midlatitudes.
Urban heat island (UHI) effect Observed higher temperatures measured in urban area compared with the surrounding rural area.
Uvala A compound sinkhole (doline) or chain of intersecting sinkholes.
Geography terms and Definitions starting with V | UPSC – IAS
Valley That portion of the total terrain in which a stream drainage system is clearly established.
Valley breeze Upslope breeze up a mountain due to heating of air on its slopes during the day.
Valley glacier A long, narrow feature resembling a river of ice, which spills out of its originating basins and flows down-valley.
Valley train A lengthy deposit of glaciofluvial alluvium confined to a valley bottom beyond the outwash plain.
Vapor pressure The pressure exerted by water vapor in the atmosphere.
Ventifact Rock that has been sandblasted by the wind.
Verbal map scale Scale of a map stated in words; also called a word scale.
Vertebrates Animals that have a backbone that protects their spinal cord—fishes, amphibians, reptiles, birds, and mammals.
Vertical zonation The horizontal layering of different plant associations on a mountainside or hillside.
Vertisol A soil order comprising a specialized type of soil that contains a large quantity of clay and has an exceptional capacity for absorbing water. An alternation of wetting and drying, expansion and contraction, produces a churning effect that mixes the soil constituents, inhibits the development of horizons, and may even cause minor irregularities in the surface of the land.
Visible light Waves in the electromagnetic spectrum in the narrow band between about 0.4 and 0.7 micrometers in length; wavelengths of electromagnetic radiation to which the human eye is sensitive.
Volcanic island arc Chain of volcanic islands associated with an oceanic plate–oceanic plate subduction zone; also simply island arc.
Volcanic mudflow A fast-moving, muddy flow of volcanic ash and rock fragments; also called a lahar.
Volcanic rock Igneous rock formed on the surface of Earth; also called extrusive rock.
Volcanism General term that refers to movement of magma from the interior of Earth to or near the surface.
Geography terms and Definitions starting with W | UPSC – IAS
Walker Circulation General circuit of air flow in the southern tropical Pacific Ocean; warm air rises in the western side of the basin (in the updrafts of the ITCZ), flows aloft to the east where it descends into the subtropical high off the west coast of South America; the air then flows back to the west in the surface trade winds. Named for the British meteorologist Gilbert Walker (1868–1958) who first described this circumstance.
warm front The leading edge of an advancing warm air mass.
waterspout A funnel cloud in contact with the ocean or a large lake; similar to a weak tornado over water.
watershed See drainage basin.
water table The top of the saturated zone within the ground.
water vapor Water in the form of a gas.
wave-cut platform Gently sloping, wave-eroded bedrock platform that develops just below sea level; common where coastal cliff is being worn back by wave action; also called wave-cut bench.
wave height The vertical distance from wave crest to trough.
wavelength The horizontal distance from wave crest to crest or from trough to trough.
wave of oscillation Motion of wave in which the individual particles of the medium (such as water) make a circular orbit as the wave form passes through.
wave of translation The horizontal motion produced when a wave reaches shallow water and finally “breaks” on the shore.
wave refraction Phenomenon whereby waves change their directional trend as they approach a shoreline; results in ocean waves generally breaking parallel with the shoreline.
weather The short-term atmospheric conditions for a given time and a specific area.
weathering The physical and chemical disintegration of rock that is exposed to the atmosphere.
westerlies The great wind system of the midlatitudes that flows basically from west to east around the world in the latitudinal zone between about 30° and 60° both north and south of the equator.
wetland Landscape characterized by shallow, standing water all or most of the year, with vegetation rising above the water level.
wilting point The point at which plants are no longer able to extract moisture from the soil because the capillary water is all used up or evaporated.
wind shear (vertical wind shear) Significant change in wind direction or speed in the vertical dimension.
woodland Tree-dominated plant association in which the trees are spaced more widely apart than those of forests and do not have interlacing canopies.
Geography terms and Definitions starting with X | UPSC – IAS
Xerophyticadaptations Plants that are structurally adapted to withstand protracted dry conditions.
Geography terms and Definitions starting with Y | UPSC – IAS
Yazoo stream A tributary unable to enter the mainstream because of natural levees along the mainstream.
Geography terms and Definitions starting with Z | UPSC – IAS
Zone of aeration (vadose zone) The topmost hydrologic zone within the ground, which contains a fluctuating amount of moisture (soil water) in the pore spaces of the soil (or soil and rock).
Zone of confined water The third hydrologic zone below the surface of the ground, which contains one or more permeable rock layers (aquifers) into which water can infiltrate and is separated from the zone of saturation by impermeable layers.
Zone of saturation (phreatic zone) The second hydrologic zone below the surface of the ground, whose uppermost boundary is the water table. The pore spaces and cracks in the bedrock and the regolith of this zone are fully saturated.
Zoogeographicregions Division of land areas of the world into major realms with characteristic fauna.