Key words Flashcards
(57 cards)
Lithosphere
The section of Earth’s profile which includes the crust and upper (solid) mantle
Asthenosphere
The uppermost part of the mantle roughly 80-200 km beneath the Earth’s surface. This is the layer than tectonic plates rest and move.
Below the lithosphere
Plate tectonics theory
Theory that the crust is divided up into smaller sections which all float on top of the mantle, and all move
Sea-floor spreading
Process by which oceanic plates split apart and new crust is formed through the rising of basaltic magma
Convection currents
Material in the mantle rises up and down. Hot material, which is less dense, moves upwards. As it cools, density increases and it sinks once again
Ridge push (gravitational sliding)
Secondary form of plate movement, caused by the heavy weight of new oceanic crust at ocean trenches
As the crust moves away from a mid-ocean ridge, it cools and becomes denser and thicker. This causes the lithosphere to slope away from the ridge and gravity pulls the lithosphere down this slope, pushing it forwards.
Slab pull
Process by which dense and old oceanic crust is pulled down under less dense continental crust at subduction zones
The pulling force exerted by a cold, dense oceanic plate plunging into the mantle due to its own weight. The theory is that because the oceanic plate is denser than the hotter mantle beneath it, this contrast in density causes the plate to sink into the mantle
Convergent boundary
Land is destroyed as two plates collide. The denser (oceanic) plate is forced (subducted) below the lighter plate and melted in the mantle
Divergent boundary
Two plates pull apart creating new land- ocean ridges or rift valleys (constructive)
Conservative boundary
Plates move past each other, but no land is destroyed. Pressure builds and is suddenly released, often as powerful earthquakes
Magma plume
Upward flow of hotter magma, than the surrounding mantle
Young fold mountains
Mountains made of thick accumulations of sedimentary rock which form along the edges of continents where two plates collide e.g. the Himalayas
Rift valley
Narrow depression between an upland area on each side, sometimes seen at divergent plate boundaries as the two plates pull apart
Ocean ridge
Area of raised seabed, where the two tectonic plates are spread apart at a divergent plate boundary
deep-sea trench
Deep depression found along the seaward edge of convergent plate boundaries.
Trenches are formed through subduction, which occurs when tectonic plates collide and push one plate beneath the other. Trenches can be found all over the surface floor of the ocean at subduction zones
Island arc
Often crescent shaped line of volcanoes protruding from the ocean along a convergent plate boundary
Plate boundary
The boundary between two tectonic plates
Hotspot
Site of a volcano away from a plate boundary as hot magma rises and melts through the crust
Shield volcano
Landform with a central vent and gently sloping sides, built up by layers of basaltic lava flows e.g. Mauna Load, Hawaii
Composite volcano
Steep-sided, pyramid-shaped landform built up from alternating layers of ash and lava flows e.g. Mount Vesuvius, Italy
High-viscosity magma
Underground material that is very sticky and silica rich e.g rhyolite and andesite, formed from melted crust at convergent boundaries
Low-viscosity magma
Underground material that flows relatively freely, with low silica content e.g. basaltic, often formed of mantle material, not melted crust
Effusive eruption
Low-magnitude volcanic ejection, such as runny basaltic lava which flows away from a vent- little height of ejecta is maintained
Explosive eruption
Violent ejection of volcanic material due to a great build-up of pressure, trapped gases and viscous magma often at a convergent plate boundary
