Cameroon GCE O-Level Geography key terms

The breakdown or decay of rocks where they lie, caused by rain, heat, frost, plants and chemical reactions. Unlike erosion, the broken material is not carried away by the process itself.

The wearing away of the land surface by moving agents such as running water, wind, waves or ice, followed by the transport of the loosened material to another place.

The total material carried by a river: dissolved minerals, fine suspended silt and clay, and coarser material rolled or bounced along the bed. Load size generally falls downstream as the current slows.

The laying down of transported rock material, soil or sediment when the carrying agent loses energy, for example where a river slows on entering a lake or the sea.

A fan-shaped spread of coarse sediment built where a steep mountain stream leaves its valley and spreads out over flatter, drier ground, losing speed and dropping its load.

A low, often triangular area of new land at a river mouth, formed as the river drops silt where its current is checked by a standing body of water. Distributary channels commonly cross it.

A broad curve or loop in a river's course. Faster water erodes the outer bank while slower water deposits sand and silt on the inner bank, so the bend shifts sideways over time.

A curved lake left behind on a flood plain when a river cuts through the narrow neck of a very tight meander, abandoning the old loop as a separate body of water.

The flat land beside a river, built up from layers of silt laid down when the river overflows its banks. It is usually fertile and attractive for farming but liable to flooding.

A natural or artificial embankment along a river bank. Natural levees form when flood water slows and drops its coarsest sediment beside the channel; artificial ones are built to hold flood water back.

The boundary of high ground separating one drainage basin from another. Rain falling on one side of the line drains to one river system, and rain on the other side to a different system.

The whole area of land drained by a river and its tributaries, bounded by a watershed. Its size, shape, rock type and vegetation all affect how quickly water reaches the main channel.

A smaller stream or river that joins a larger one. Tributaries add water and load to the main channel and are usually named separately in maps and diagrams.

The diversion of the upper part of one river into the valley of a neighbouring, more deeply cut river. The captured stream loses its headwaters and may be left as a misfit stream.

The pattern of a river's flow through the year, showing months of high and low water. It reflects rainfall pattern, evaporation, vegetation, soil and the presence of dams or lakes upstream.

The removal of a thin, fairly even layer of topsoil by rainwash or wind over a wide slope, rather than by concentrated channels. It is easily missed but reduces fertility steadily.

The cutting of deep, narrow channels into soil and soft rock by concentrated running water. Once started, gullies deepen upstream and can destroy farmland and roads.

A vertical section through soil from the surface down to the underlying rock, showing distinct layers or horizons. Each horizon differs in colour, texture, organic content and depth.

The washing downward of dissolved plant nutrients and minerals through the soil by heavy rainfall. It leaves upper layers poorer and can make tropical soils acidic and infertile.

The theory that the Earth's outer shell is broken into large rigid plates that move slowly over the mantle. Their collisions, separations and sliding past one another cause earthquakes, volcanoes and fold mountains.

A fracture in the Earth's crust along which rock masses have moved relative to each other. Movement may be sudden, producing an earthquake, or slow and repeated over long periods.

The point on the Earth's surface directly above the focus, where an earthquake begins underground. It usually suffers the strongest shaking, though local geology can change the pattern.

An instrument that records the shaking of the ground during an earthquake, producing a trace called a seismogram. Records help scientists locate the focus and compare the strength of tremors.

A vent or opening in the Earth's crust through which molten rock, ash and gases escape, often building a cone of lava and ash around it. Most occur near plate boundaries.

Molten rock that has reached the Earth's surface and flows out of a volcano or crack. Once cooled and hardened it becomes solid rock, which may be rough or smooth depending on its composition.

A long, narrow trough of land between two roughly parallel faults, formed where the crust has been pulled apart and a block has sunk. Steep straight sides are typical.

A mountain range formed where thick layers of rock are compressed and buckled upward into folds by the collision of plates. The Himalayas and the Alps are familiar examples.

The overall wearing down of the land by weathering, erosion, transport and deposition acting together over long periods. It is the general term for the processes that lower the land surface.

The average number of people living in a unit of area, usually expressed per square kilometre. It hides local variation, since people cluster in towns and fertile areas.

The way people are spread across a country or region, whether evenly or concentrated in certain places. Relief, climate, soil, jobs and transport routes largely explain the pattern.

The movement of people from one place to another to live, either within a country or across borders. Push factors drive people out; pull factors attract them elsewhere.

The growing proportion of a population living in towns and cities, together with the physical expansion of built-up areas. It is driven by rural-to-urban migration and natural increase.

An official count of a country's population, normally taken at regular intervals, recording details such as age, sex, occupation and place of residence for planning purposes.

The number of live births per thousand people in a population in a given year. It is compared with the death rate to show whether a population is growing naturally.

The number of deaths per thousand people in a population in a given year. Falling death rates, often from better medicine and food supply, are a main cause of rapid population growth.

The increase in a population over time, resulting from the balance of births over deaths plus the balance of immigrants over emigrants. It may be rapid, slow, or negative.

The average pattern of weather in a place over many years, including temperature, rainfall and winds. It differs from weather, which is the day-to-day condition of the atmosphere.

The condition of the atmosphere at a particular place and time, described by temperature, humidity, cloud, wind and rainfall. It changes from hour to hour and day to day.

Water falling from clouds to the ground as rain. It may be relief rain, forced up by hills; convectional rain, from heated rising air; or frontal rain, where warm and cold air meet.

A long period with much less rain than normal for the area, so that rivers, wells and soils dry out. It damages crops and livestock and can cause food shortages.

The spread of desert-like conditions into neighbouring dry land, usually through overgrazing, tree felling, poor farming and drought. Fertile land gradually loses its vegetation and soil.

The plant cover of an area, such as forest, savanna grassland, scrub or marsh. Its type depends mainly on rainfall, temperature and soil, and it protects the ground from erosion.