Palaeogeography The study of the geography of geological periods is called palaeogeography.
Pallid Zone Pallid zone refers to a horizon of decomposed Kaolinitic clay and quartz sand occurring above deeply weathered bedrock in the tropics. It is characterised by the virtual absence of iron minerals.
Pampas (Pampa) Pampas or pampa refers to the extensive temperate grasslands of Argentina and Uruguay in South America.
Pampero Pampero is the name given to a cold, dry polar air blowing northwards or north-eastwards across the pampas of South America. It resembles a.line squall with
very dark clouds.
Pangaea The term pangaea, coined by A. Wegener, refers to a primeval supercontinent which is believed to have broken up about 200 million years ago in Mesozoic era to form two segments: Laurasia in the Northern Hemisphere and Gondawana land in the Southern Hemisphere. Pangaea was surrounded by a hypothetical sea known as Panthalassa.
Parallel A line of latitude running down the earth parallel to the equator is called parallel. The parallels decrease in length away from the equator until they are replaced at each pole by a point. The equator is the only line of latitude that is a great circle. All other parallels are small circles.
Parautochthonobs Parautochthonous refers to folded and transported bodies of rock, generally in nappe structures, that have been displaced a long distance from their root zone.
Parhelion (Mock Sun) An image of the sun which appears as an intensely bright spot on or near to the sun halo is known as parhelion or mock sun. Parnelion is caused by the refraction of sunlight by a particular type of ice crystal, especially in cirrus clouds. It is brighter than the mock moon (paraselene).
Paternoster Lakes Paternoster lakes refer to a series or chain of lakes in a glaciated valley. The lakes are usually separated from each other by dams of moraine or by rock bars.
Peat Peat is an unconsolidated black or dark-brown soil material consisting largely of slightly decomposed fibrous vegetable matter that has accumulated in a waterlogged environment. Peat occurs mainly in cool moist climates where drainage is poor.
Pedalfer A major division of soils in the USA, pedalfer is a free-draining zonal soils of humid climates in which leaching has removed base compounds so that soil becomes generally acidic. Examples of pedalfer include latosols and prairie soils.
Pediplain (Pediplane) A pediplain or pediplane is an extensively eroded surface of low relief. It is thought to have been produced by the coalescence of several pediments (a pediment is a gentle slope, cut in bedrock). It is a smooth surface with a gently conClave profile and with relatively few streams.
Pele's Hair The term Pele's hair refers to fine threads or filaments of volcanic glass produced during volcanic eruption. Pele's tears are tiny droplets (6-13 mm in length) of volcanic glass rejected during a volcanic eruption. They are named after Pele, the Hawaiian goddess of fire.
Peneplain Regarded as the and product of the normal cycle of erosion, a peneplain is an area of low relief. A peneplain is thought to have been formed by the widening of flood plains and the wearing down of interfluves by subaerial denudation. Monadnocks are occasionally found in it.
Perigee Perigee is the point in the orbit of the moon when it is the closest to the earth. It contrasts with apogee which is the point in the orbit of the moon when it is farthest from the earth. Perigee is also defined as the point in the orbit of any planet when it is nearest to the earth.
Period A period is defiJ\ed as a geological time interval. The corresponding division of rocks is a system. Each period is divided into a number of Epochs and several periods make up an Era.
Peru Current Also called the Humboldt current, Peru current is a cold current which flows northwards along the western coastline of South America.
Phacolith The term phacolith refers to an intrusion of igneous rock in a lens-shaped manner. A concordant intrusion, a phacolith usually occupies the crest of an
anticline.
Photochemical Fog Photochemical. fog is defined as a state of poor visibility caused by the chemical reaction of sunlight on- hydrocarbons in the atmosphere.
Peidmont Piedmont, a French term for the foot of a mountain, is defined as the gentle slope leading down forin the steep mountain slope to the plains. In other words, peidmont is a landform stretching between the mountain slopes and a flat lowland.
Pitchblende A form of uraninite, pitchblende is the most important ore of uranium. It is found chiefly in hydrothermal veins. The Great Bear Lake (Canada) and Zaire are among the chief pitchblende regions of the world.
Plain A plain is defined as an extensive tract of flat land or gently undulating terrain without prominent hills or depressions.
Plaination Plaination is the procesS by which an area of the earth's surface is denuded. by subaerial or marine agencies to produce a flat surface or surface of low relief.
Planetary Winds The term planetary winds refers to the general air movements within the earth's atmospheric circulation. The wind belts are basically controlled by two factors: latitudinal pressure belts and longitudes.Trade winds, temperate westerlies and polar westerlies come under the category of planetary winds.
Planetimal Hypothesis Planetismal hypothesis, proposed by F.R. Moulton and T.e. Chamberlin in 1904, states that the planets of the solar system were created by the coalescence of numerous tiny planets--planetismalsdue to gravitational attraction of collision. This hypothesis contrasts with the nebula hypothesis.
Plankton Plankton refers to very small animals and plants, such as diatoms and algae, that form the drifting organic life of the surface layers of the ocean.
Planosol Planosol is the name given to an intrazonal soil of poorly-drained areas. It is a strongly leached soil which develops under humid climates and where there is a high degree of waterlogging.
Plateau An extensive elevated area of relatively flat land is termed a plateau.
Plate Tectonics The term plate tectonics refers to the theory that the outer shell of the earth is made up of a number of relatively thin lithospheric plates composed of oceanic and continental crust. Seven major and twelve smaller plates have been recognised.
Plinian Eruption Plinian eruption, named after Pliny the Younger, who observed the eruption of Vesuvius in AD 79, refers to a volcanic eruption in which the explosion cloud towers to great heights (up to 50 km) in the shape of a pino, the Latin term for pine tree.
Plucking Plucking is the process of glacial erosion in which ice freezes to shattered rock on the bed of a glacier and carries it away.
Plume The term plume refers to the mechanism in which rocks in the earth's mantle begin to melt, thus becoming less dense and rising towards the surface. The process is most frequently observed in the regions where continuous volcanic activity occurs.
Pheumatolysis The process in which chemical changes occur in rocks owing to the action of hot gaseous substances during igneous activity is known as pneumatolysi&.
Podzol A Russian term, podzol refers to a zonal soil that is formed in cool humid climates under heath and coniferous forests. The true podzol has a thin layer of raw humus. Podzol soils occur across the former USSR and North American regions. Podzolisation is the process by which podzol soils are formed.
Polar Front Zet (PFZ) Stream The high velocity air flow of the jet stream at latitude 45° is called polar front zet (PFZ) stream. PFZ stream is more marked in the Northern Hemisphere.
Polymict The term polymict refers to a detrital rock which is composed of fragments of different matenals. Polymict rocks are characteristic of geo-synclinical regions and include graywackes.
Pot-hole A pot-hole is a circular hole in the rocky bed of a stream. It is also defined as a steep-sided shaft in limestone terrain or Karst down which a surface stream disappears.
Prairie Prairie is the name given to the extensive, treeless grassy plains of North America. It is developed under 250-500 mm rainfall, most of which occurs in summer. It is characterised by high summer temperatures and low winter temperatures. A dark-coloured soil occurring in the mid-latitude 'zone beneath the temperate grasslands is known as prairie soil.
Precipitation Precipitation is the deposition of water solid or liquid form on the earth's surface from al spheric sources. Dew, drizzle, hail, rain, etc., are diffE forms of precipitation.
Pressure Gradient The rate of change of atrnospt pressure between two points on the earth's surfa( called pressure gradient. Pressure gradient is indic
on a weather chart by spacing the isobars. A s gradient indicates strong winds and a gentle one, sJ winds.
Prevailing Wind The wind that blows most frequentl: any location is called prevailing wind.
Prime Meridian Prime meridian is the meridian on earth's surface from which longitude is .measured. I Greenwich Meridian is taken as prime meridian. I
Pseudomorph The term pseudomorph refers to a mini that has replaced another mineral and assumed I external form, e.g., gypsum replacing anhydride.
Psychrometer Psychrometer is an instrument used measure the relative humidity of the air.
Pumice Pumice is the name given to a cellular or vesicl igneous rock with a sponge-like structure. It is so that it floats in water.
Pyrometer Pyrometer is an instrument used for measure the temperature of molten lava.
Pyroxenes The term pyroxenes refers to a group of silic rock-forming minerals. Pyroxenes are found most ab1 dantly in basic and ultrabasic rocks.
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