JCE Geography key terms

The theory that Earth's outer shell is broken into rigid slabs that move over the softer mantle, so their collisions, separations, and slides cause earthquakes, volcanoes, and mountain building.

The cool, rigid outer layer of Earth made of the crust plus the uppermost mantle, which is cracked into tectonic plates that shift slowly over time.

The hot, partly molten and slowly flowing layer of the mantle beneath the lithosphere. Its movement allows tectonic plates above to slide and is linked to magma generation.

A plate margin where two plates move toward each other. The result may be subduction, deep ocean trenches, fold mountains, or volcanic island arcs, depending on the crust involved.

A plate margin where plates pull apart. Magma rises into the gap, forming new crust along mid-ocean ridges or producing rift valleys on continents, with shallow earthquakes.

The process where a denser oceanic plate sinks beneath another plate at a convergent margin, creating trenches, earthquakes, and magma that feeds volcanic arcs.

A long underwater mountain range where plates diverge and new oceanic crust forms. Ridges are cut by transform faults and are sites of shallow earthquakes and basalt volcanism.

The gradual addition of new oceanic crust at mid-ocean ridges as magma rises and cools, pushing older crust outward and producing symmetrical magnetic patterns on the sea floor.

The record of past magnetic field direction and strength preserved in rocks. Stripes of alternating polarity on the ocean floor provide key evidence for sea-floor spreading.

A fixed zone of rising mantle heat that melts the plate moving over it, producing chains of volcanoes such as Hawaii. The chain's age pattern reveals plate motion direction.

A curved line of volcanoes above a subducting plate, formed as rising magma reaches the surface. Examples include the Andes and the island arcs of the western Pacific.

A narrow, very deep depression in the ocean floor where a subducting plate bends downward. Trenches mark the deepest parts of the oceans and border many volcanic arcs.

A mountain range formed when compressional forces crumple rock layers into folds, often at a convergent plate margin. The Himalayas and Alps are classic examples.

The processes of mountain building, including folding, faulting, and uplift of crust, usually driven by plate convergence over millions of years.

The breakdown of rock in place by physical, chemical, or biological processes. It produces loose material but does not itself transport the broken fragments away.

The removal and transport of weathered rock and soil by agents such as running water, wind, ice, and waves. It shapes valleys, coasts, and sediment deposits.

The laying down of eroded sediment when the transporting agent loses energy, for example where a river slows, a glacier melts, or wind drops its load.

The downslope transfer of soil and rock under gravity, ranging from slow creep to fast landslides and mudflows. Water content and slope angle strongly influence it.

The movement of sediment along a coast by waves approaching at an angle, carrying material in a zigzag pattern and building features such as spits and bars.

The volume of water passing a point in a river per unit time, usually measured in cubic metres per second. It rises after heavy rain and falls in dry spells.

A graph showing river discharge over time after rainfall. Its lag time and peak height reveal how quickly water reaches the channel and how the basin stores it.

The area of land drained by a river and its tributaries, bounded by a watershed. Its size, shape, soil, and land cover affect how rainfall becomes river flow.

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

A low, often fan-shaped deposit of sediment where a river enters a slow-moving or standing body of water and loses velocity, dropping its load.

The flat land beside a river that is covered during floods. Repeated deposition of fine sediment makes floodplains fertile but also prone to flood damage.

A steep drop in a river's course where the water falls over resistant rock or a sudden change in gradient, often undercutting softer rock below.

A large mass of ice that forms on land from compacted snow and flows slowly downhill under its own weight, eroding and depositing rock debris.

A bowl-shaped hollow on a mountainside carved by a glacier, often holding a small lake after the ice melts. Also called a cirque or cwm.

An accumulation of unsorted rock debris deposited directly by a glacier, found at its sides, base, or farthest advance and used to reconstruct past ice limits.

The average pattern of weather in a place over many years, including typical temperatures, rainfall, and seasonal variation, distinct from short-term daily weather.

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

A large body of air with fairly uniform temperature and humidity, formed over a sea or land surface. Its source region and path determine the weather it brings.

The boundary between two air masses of different temperature and density. Warm and cold fronts bring characteristic cloud and rainfall patterns as they pass.

The climate of a small area such as a garden, valley, or city street, which differs from the surrounding region because of local shelter, surface, or elevation effects.

The tendency of built-up areas to be warmer than nearby countryside, caused by dark surfaces absorbing heat, low vegetation, and heat released by buildings and traffic.

The number of people living in a given area, usually expressed per square kilometre. It reveals how crowded a place is but hides uneven distribution within it.

The way people are spread across an area, from dense cities to sparsely settled uplands. Relief, climate, soil, and economic opportunity all influence the pattern.

The movement of people from one place to another to live, for a season or permanently. Push factors such as conflict or poverty and pull factors such as jobs drive it.

The rising share of a population living in towns and cities, driven by rural-to-urban migration and natural growth. It brings both economic opportunity and pressure on services.