CSEC Geography key terms

The breakdown and decay of rock in place under the influence of weather, water, plants and chemical reactions, without the material being carried away. It may be mechanical, chemical or biological.

The wearing away of rock and soil by moving agents such as running water, wind, waves and ice, and the transport of the loosened material to another place. It differs from weathering because material is removed.

The laying down of material that a transporting agent can no longer carry, for example when a river slows on entering the sea or when wind loses speed behind an obstacle. Deposits build landforms such as deltas and dunes.

The theory that the Earth's outer shell is broken into large rigid slabs that drift slowly over the mantle. Their collision, separation and sliding past one another explain earthquakes, volcanoes and fold mountains.

The process in which a denser oceanic plate sinks beneath a lighter continental or oceanic plate at a converging boundary, producing deep ocean trenches, volcanic arcs and strong earthquakes.

High mountain ranges formed where compressional forces at a converging plate boundary crumple sedimentary layers into large upfolds and downfolds, often with volcanoes and earthquakes nearby.

A fracture in the Earth's crust along which rocks have moved. Sudden slippage along a fault releases stored energy as an earthquake, and the ground surface may be offset.

A sudden shaking of the ground caused by the release of energy when rocks break or slip along a fault. Strength is recorded by magnitude and shaking intensity by the Mercalli scale.

Energy travelling through the Earth as vibrations from an earthquake or explosion. Body waves pass through the interior and surface waves travel along the crust, causing most damage.

An instrument that detects and records ground vibrations, producing a trace called a seismogram. The arrival times of different waves help locate an earthquake's focus and estimate its magnitude.

An opening in the Earth's crust through which magma, gases and ash escape, often building a cone. Most occur near plate boundaries or over hot spots in the mantle.

Molten rock beneath the Earth's surface. It rises because it is less dense than surrounding rock, and once it reaches the surface through a vent it is called lava.

A fixed plume of unusually hot mantle material that melts the plate moving over it, creating a chain of volcanic islands. The Hawaiian islands are the classic example.

A series of long waves generated when a large volume of water is displaced, usually by an undersea earthquake, landslide or volcanic eruption. Waves grow tall in shallow coastal water and can flood far inland.

The whole area of land drained by a river and its tributaries, bounded by a watershed. Rain falling anywhere inside it eventually reaches the main river channel.

The boundary of high ground separating one drainage basin from another. Rain falling on opposite sides of a watershed flows into different river systems and eventually different seas.

A smaller stream or river that joins a larger one, adding water and sediment. Tributaries branch like a tree within a drainage basin and increase discharge downstream.

The volume of water flowing past a point in a river in a given time, usually measured in cubic metres per second. Discharge rises downstream and after heavy rainfall.

The flat land beside a river that is covered when the river overflows its banks. Repeated floods deposit fertile alluvium, which makes such land attractive for farming despite the risk.

A raised bank of sediment deposited along a river channel when floodwater slows and drops its load. Artificial levees are built higher to protect land from flooding.

A triangular or fan-shaped area of sediment built where a river enters a lake or sea and loses velocity, dropping its load. Distributaries often branch across the delta.

The movement of sand and pebbles along a coast in a zigzag path, as waves approach at an angle and swash carries material up the beach while backwash returns it straight down.

A narrow ridge of sand or shingle extending from the land into the sea, built where longshore drift continues past a change in the coastline and deposits material in open water.

The gently sloping strip of loose sediment between low and high water marks, shaped by waves. Constructive waves build it up while destructive waves remove material.

The downhill transfer of soil and rock under gravity, either slowly as creep or rapidly as a landslide or mudflow. Water soaking the material and steep slopes increase the risk.

The average pattern of weather in a place over many years, including typical temperatures, rainfall and seasonal changes. It differs from weather, which describes short-term conditions.

The state of the atmosphere at a particular place and moment, described by temperature, humidity, wind, cloud and precipitation. It changes from hour to hour and day to day.

Water falling from clouds to the ground as drops. It forms by convectional, relief or frontal lifting of moist air, and its seasonal pattern strongly influences farming and water supply.

A prolonged period of abnormally low rainfall that reduces soil moisture, river flow and water supplies. It damages crops, can cause famine and is often worsened by high evaporation.

The spread of desert-like conditions into dry but previously productive land, usually through overgrazing, deforestation, poor irrigation and drought. Topsoil and vegetation are lost.

The removal of the fertile top layer of soil by wind or water faster than it can form. Bare, sloping or overcultivated ground is most vulnerable and yields fall.

The average number of people living in a unit area, usually expressed as persons per square kilometre. It is calculated by dividing total population by total land area.

The way people are spread across a country or region, which may be clustered in cities, along coasts or thinly spread in mountains and deserts. It is shown on a dot map.

A graph showing the number of males and females in each age group of a population. Its shape reveals whether a country has high birth rates, a youthful population or an ageing one.

The number of live births per thousand people in a population in one year. Together with the death rate it determines whether a population grows naturally.

The growing proportion of a population living in towns and cities, caused by rural-to-urban migration and natural increase. It brings both economic opportunity and pressure on housing and services.

The permanent or semi-permanent movement of people from one place to another. Push factors such as unemployment drive people out, while pull factors such as jobs attract them in.

Meeting the needs of people today without destroying the resources and environment that future generations will depend on. It balances economic growth, social welfare and environmental care.

The large-scale clearing of forest, usually for farming, timber or settlement. It destroys habitats, exposes soil to erosion, and can increase flooding and carbon dioxide in the atmosphere.

The careful management and protection of natural resources so that they are not wasted or destroyed. It includes setting aside reserves, replanting trees and controlling hunting and fishing.