Tectonics, Hazards, Volcanoes, Climate, Weather, Weathering
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Landslide
A fall of loose earth and rock down a slope under the force of gravity, usually when it is saturated by heavy rain.
Mudflow
A powerful current of water mixed with mud, rocks and boulders running down a river channel, valley or slope.
Earthquake
The violent shaking of the upper layers of the Earth when energy is released as the rocks crack and move.
Epicentre
The point on the Earth’s surface directly above an earthquake’s focus.
Fault
A crack in the rocks of the Earth’s crust where the rocks move and are displaced.
Mercalli Scale
A 12-point scale that describes the effects of an earthquake.
Pyroclastic
The solid material produced during a violent volcanic eruption. A pyroclastic flow is the rapid flow of this material down the side of a volcano. Pyroclastic flows are responsible for many of the deaths from volcanic eruptions, because they move so quickly.
Radioactivity
The process of the breakdown of the nuclei of unstable atoms, releasing heat and radioactive energy.
Richter Scale
A 10-point scale measuring the total amount of energy released by an earthquake.
Shearing
A type of stress where forces cut across each other.
Shield volcano
volcano A large volcano with gentle sides, built up by non-viscous lava and very little ash.
Stratovolcano
A volcano made from alternate layers of lava and ash. It is also known as a composite cone.
Tsunami
An ocean wave produced when there is movement of the seabed caused by the fault movement that causes an earthquake. A tsunami can also be caused by the collapse of a volcanic cone into the sea.
Volcano
A hill or mountain built up by the eruption and build-up of lava at the surface. The term is sometimes used for anywhere that lava is erupting.
Compression
A type of stress that involves forces meeting from opposite directions.
Conservative plate margin
A plate margin where two plates slide past each other and no plate is either created or destroyed.
Constructive plate margin
A plate margin where two plates diverge and new oceanic plate is created in the gap.
Convection currents
Currents in liquids and gases caused by heating. Heated material becomes less dense and rises. It then diverges, cools and descends – forming a series of circulation cells.
Crust
The outer layer of the Earth (between 6 and 90 km thick), which has a different composition to the layer below.
Destructive plate margin
A plate margin where two plates converge and one is destroyed (by being subducted beneath the other plate and melting).
Downfold
Where rocks have been crumpled in a downwards direction, like a letter U.
Focus
The point in the Earth where an earthquake occurs.
Fold mountains
Long ranges of mountains formed by the compression and crumpling of rock layers, e.g. the Himalayas.
Island arc
A chain of islands forming a crescent shape. It is formed from volcanoes at a destructive plate margin which involves two oceanic plates.
Mantle
The middle layer of the Earth between the crust and the core.
Ocean ridge
A broad, high belt of ocean floor that is much higher than the surrounding area. It is formed by volcanic activity at constructive plate margins, e.g. the Mid-Atlantic Ridge.
Ocean trench
A long, narrow area of ocean floor (about 10 kilometres deep), usually found at a destructive plate margin at the edge of an ocean.
Partial melting
A process taking place deep in the Earth where extreme heat causes very small areas of the rocks to melt. These are able to come together to form large masses of magma.
Plastic solid
A solid which can flow and be deformed without fracturing.
Plate
The upper, colder, rigid parts of the Earth’s surface, made up of the crust and upper mantle.
Plate margin
Where two plates meet.
Plate tectonics
The concept that the Earth’s surface is made up of a number of rigid sections that can slowly move over time.
Stress
The force per unit area acting on an object.
Subduction
The process where plates converge and one plate is forced beneath the other.
Tension
A type of stress where forces pull in opposite directions, causing stretching.
Upfold
Where rocks have been crumpled in a upwards direction like an upside down letter U.
Ash
The fine dust produced by a volcanic eruption.
Composite cone
See stratovolcano.
Crater
The depression at the top of a volcano.
Dormant
A volcano which has not erupted for some time, but which might erupt again in the future.
Extinct
A volcano that will never erupt again.
Lahar
A mudflow which contains material from volcanic eruptions.
Lateral blast
When a volcano erupts sideways with great force – producing gas and pyroclastic material.
Lava
Molten rock on the Earth’s surface.
Magma
Molten rock below the Earth’s surface.
Magma chamber
A huge chamber (several kilometres across), which stores molten rock beneath a volcano.