Tamil Nadu HSE First Year Geography key terms

The study of the Earth's surface as the home of humans, examining how natural features and human activities are distributed, how they interact, and why they differ from place to place.

The branch of geography that studies one theme, such as climate, soil, or population, across the whole world rather than within a single region.

The branch of geography that studies all physical and human features of one defined area together, showing how they combine to give that area its character.

The branch of physical geography that studies landforms, their shapes and distribution, and the erosion and deposition processes that create and change them over time.

The chronological framework dividing Earth's 4.6-billion-year history into eons, eras, periods and epochs, based on rock sequences and the fossils they contain.

The principle that the same natural processes operating today, such as erosion and volcanism, also shaped the Earth in the past, so present processes explain ancient rocks.

The concentric divisions of the Earth into crust, mantle and core, identified from seismic wave behaviour, with density and temperature increasing toward the centre.

The boundary surface separating the Earth's crust from the mantle, marked by a sudden increase in seismic wave velocity at roughly 30 to 70 km depth beneath continents.

Vibrations released by earthquakes that travel through the Earth; P waves and S waves bend and change speed at internal boundaries, revealing the planet's layered structure.

The theory that the lithosphere is broken into rigid plates that move over the asthenosphere, causing earthquakes, volcanism, mountain building and the drifting of continents.

The process where magma rises at mid-ocean ridges, solidifies, and pushes newly formed ocean floor outward on both sides, creating new crust and widening ocean basins.

A plate margin where two plates move toward each other, producing subduction, deep ocean trenches, volcanic arcs and fold mountains such as the Himalayas.

A mountain range formed when layered sedimentary rocks are compressed and buckled into folds by converging plates, as in the Himalayas and the Alps.

The breakdown of rocks in place by physical, chemical or biological processes, without any transport of the broken material away from the site.

The removal and transport of weathered rock material by agents such as running water, wind, ice or waves, which carves valleys and shapes landforms.

The laying down of eroded material when the transporting agent loses energy, building features such as deltas, floodplains, sand dunes and moraines.

A fan-shaped tract of sediment deposited where a river enters a sea or lake and its flow slows, common on India's east coast and in Tamil Nadu's Cauvery mouth.

Incoming solar radiation received at the Earth's surface, varying with latitude, season, duration of daylight and atmospheric transparency, and driving atmospheric circulation.

The proportion of incoming solar radiation reflected back to space by a surface; fresh snow reflects most, while dark ocean and forest surfaces reflect little.

A reversal of the normal lapse rate in which temperature rises with height in a shallow layer, trapping pollutants and often forming on clear, calm winter nights.

The rate at which temperature decreases with increasing altitude in the troposphere, averaging about 6.5 degrees Celsius per kilometre of ascent.

The lowest atmospheric layer, roughly 8 km thick at the poles and 18 km at the equator, containing most water vapour and nearly all weather phenomena.

An apparent deflecting force caused by the Earth's rotation that turns moving air and water to the right in the Northern Hemisphere and to the left in the Southern.

The difference in atmospheric pressure between two places over a given distance; the steeper the gradient, the faster the wind blows from high to low pressure.

Steady winds blowing from the subtropical high-pressure belts toward the equatorial low, from the northeast in the Northern Hemisphere and southeast in the Southern.

A seasonal reversal of prevailing wind direction, which in India brings moist southwest winds and heavy rain from June to September and dry northeast winds in winter.

The amount of water vapour present in the air, expressed as absolute humidity in grams per cubic metre or as relative humidity, a percentage of saturation capacity.

The change of water vapour into liquid droplets or ice crystals when air cools to its dew point, forming dew, fog and cloud, the necessary first step toward rainfall.

Water falling from clouds to the ground as rain, snow, sleet or hail, produced when moist air rises, cools, condenses and droplets grow heavy enough to fall.

The mass of dissolved salts in seawater, usually about 35 parts per thousand; it is highest in warm, dry subtropical seas and lower near the equator and river mouths.

Large-scale, persistent movements of surface seawater driven by prevailing winds and deflected by the Coriolis force, warming or cooling adjacent coasts.

The periodic rise and fall of sea level caused mainly by the gravitational pull of the Moon and Sun, producing two high and two low tides in about 24 hours 50 minutes.

The loose surface layer of weathered rock and organic matter in which plants grow, developing distinct horizons over long periods under climate and vegetation.

A vertical section through soil showing its horizons, typically an organic top layer, a mineral A horizon, a leached B horizon and weathered parent material below.

A large natural region defined by its climate and dominant vegetation, such as tropical rainforest, savanna, desert, grassland or boreal forest, each with characteristic animals.

The variety of living organisms at genetic, species and ecosystem levels; India is a megadiverse country with biodiversity hotspots such as the Western Ghats.

A model describing the shift of a population from high birth and death rates to low ones through intermediate stages of rapid growth as health and living standards improve.

The average number of people living per unit area, usually persons per square kilometre, obtained by dividing total population by total land area.

The movement of people from one place to another for work, education, marriage or safety, which may be internal within a country or international across borders.

A place where people live permanently, ranging from isolated rural hamlets to compact towns and sprawling cities, classified by size, function and layout.

The acquisition of information about the Earth's surface from a distance, using sensors on satellites or aircraft that record reflected or emitted energy.

A computer system for capturing, storing, analysing and displaying spatially referenced data as layers, used for planning, mapping and resource management.

A large-scale map using contour lines and symbols to show relief, drainage, settlements and land use, such as those issued at 1:50,000 scale by the Survey of India.

A line on a map joining points of equal elevation above sea level; the spacing of contours shows slope steepness and their pattern reveals landform shape.

The fertile Cauvery delta in eastern Tamil Nadu, a flat alluvial plain of rice cultivation and ancient irrigation channels, often called the state's rice bowl.

A north-south mountain escarpment along western Tamil Nadu and Kerala, a biodiversity hotspot and the source of major rivers such as the Cauvery.