Geographical Terms : Letter D

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 weath­ering, 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 qrain­age, discordant drainage is a drainage pattern which has not developed a systematic relationship with the under­lying 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 inter­tropical 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, steep­sided 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. Coastal dunes are