Geography AQA Tetonics A Level Key Definitions Essay

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Geography Key Words (Tectonics)

Palaeomagnetism –
Palaeomagnetism is the branch of geophysics concerned with the magnetism in rocks that was induced by the earth's magnetic field at the time of their formation.
Convection Currents –
As semi-molten rock in the mantle is heated it becomes less dense than its surroundings and rises. As it reaches the crust above, it spreads out carrying the plates above with it. As the semi-molten rock then cools, it gradually sinks back down to be re-heated. These convection currents are created by heat from within the earth - much of which is generated by radioactive decay in the core.
Moho discontinuity – the discontinuity between the crust and the mantle of the earth, occurring at depths that average about 22 miles (35 km) beneath the continents and about 6 miles (10 km) beneath the ocean floor.
Alfred Wegener –
Alfred Wegener proposed the theory of continental drift at the beginning of the 20th century.
Pangea –
Supercontinent term made by Alfred Wegener
Constructive (divergent) margins -
Where convection currents rise and diverge, the high temperatures can cause a doming effect on the crust as well as forces causing it to pull apart.
Destructive (convergent) margins -
With two types of plate, there are three types of margin.
Conservative margins -
Sometimes known as slip margins- two parallel plates meet.
Hot Spots -
Occur away from plate boundaries.
Benioff Zone -
Benioff zone is an inclined zone in which many deep earthquakes occur, situated beneath a destructive plate boundary where oceanic crust is being subducted.
Lithosphere -
Lithosphere is the rigid outer part of the earth, consisting of the crust and upper mantle.
Asthenosphere -
Asthenosphere is the upper layer of the earth's mantle, below the lithosphere, in which there is relatively low resistance to plastic flow and convection is thought to occur.
Geosyncline -
Geosyncline is when a portion of the earth's crust subjected to downward warping during a large span of geologic time
Transform Faults -
Transform Faults are a horizontal slip fault or a strike-slip fault occurring at the boundary between two plates of the earth's crust
Guyots –
Guyots are flat-topped submarine mountains, common in the Pacific Ocean, usually an extinct volcano whose summit did not reach above the sea
Isostatic Uplift -
Uplift in a land mass resulting from tectonic processes
Active –
A volcano that has erupted recently and is likely to erupt again. There are around 550 of these in the world.

Dormant -
A volcano that has erupted in the past 2,000 years but not recently. These are dangerous because we don’t know when these may erupt again.
Extinct -
A volcano that is unlikely to ever erupt again because their volcanic activity is finished. The last volcano erupted in Britain 50 million years ago.
It is relating to, consisting of, or denoting fragments of rock erupted by a volcano
Vent –
Vents are openings in the Earth's crust from which molten rock and volcanic gases escape onto the ground or into the atmosphere.
Basaltic –
Basaltic lavas originate largely from the upward movement of mantle material. They are found at constructive plate margins.
They are most common along spreading ridges but are also found at hot spots and within more developed rift systems. It has less gas in it as most of it escapes easily. It is less viscous which means it can flow faster and further. As a result, eruptions of basaltic lava usually aren't violent.
Andesitic –
Andesitic lavas are typical of destructive plate margins. They have higher viscosities and so they flow less easily. Volcanic gases cannot escape easily from andesitic lava. They often form blockages in volcanic vents and pressure builds up until it is released as a violent eruption.
Rhyolitic –
Rhyolitic lavas are most often found at destructive and collision margins.