GCSE Restless Earth Denfintions Flashcards
Define the following key terms.
Volcano
An opening in the earth’s crust through which molten lava, ash, and gases are ejected
Earthquake
A sudden movement of the earth’s crust creating seismic waves
Plate boundary
The border between two adjacent lithospheric plates classified by the direction in which the plates move
Oceanic crust
Lithosphere found under the oceans primarily composed of basalt; thinner but denser than continental crust ranging from 7 to10 km thick
Continental crust
Lithosphere which forms the continents and the areas of shallow seabed close to their shores made primarily of granite, ranging from 25 to 75km thick
Lithosphere
The outer part of the earth, consisting of the crust and upper mantle, approximately 100 km thick
Hotspot
A portion of the Earth’s surface that experiences volcanism due to a rising mantle plume usually far from tectonic plate boundaries.
Convergent plate boundary
A tectonic boundary where two plates collide. Plates of equal density form fold mountains; plates of unequal density form volcanoes as a result of subduction
Divergent plate boundary
A tectonic boundary where two plates separate and new crust is formed
Conservative plate boundary
A tectonic boundary where two plates move sideways past each other at different speeds. No volcanoes form
Pyroclastic flow
A fast-moving avalanche of superheated gas, lava, ash and rock ejected explosively from a volcano with speeds of 700km an hour and temperatures of about 1,000 degrees
Lava
Molten rock that reaches the earth’s surface through a volcano or fissure
Focus
The point below the Earth’s surface where seismic waves originate during an earthquake. It is where the energy stored in the rock is first released
Epicentre
The point on the Earth’s surface directly above the focus of an earthquake
Plate tectonics
A theory that explains the global distribution of earthquakes, volcanoes, continental drift Plate tectonics and mountain building caused by the interaction of the earth’s lithospheric plates
Mantle
A layer between the crust and the outer core, about 2,900km thick. Consists of magma which is viscous
Magma
Molten material beneath or within the earth’s crust, from which igneous rock is formed
Mercalli scale
Measures the effects of an earthquake through observational methods
Richter scale
Measures the magnitude of an earthquake using seismometers and seismographs
Magnitude
A measure of the strength of seismic waves
Sesimometer
An instrument that measures ground movements, usually placed underground
Seismograph
An instrument that displays the readings of seismometers in graphical form
Ocean trench
Deep, long and narrow depressions 3-4km from the sea floor located at subduction zones
Fold mountains
Mountain chains formed as a result of the collision of twotectonic plates
Fumarole
An opening in the earths crust through which steam and gases pass.
Geyser
An opening in the earths crust through which hot water and steam is intermittently ejected
Seamount
A volcano that rises from the ocean floor but does not reach to the water’s surface
Island arc
A chain of volcanic islands that have formed as a result of the convergence of two oceanic plates
Convection current
The movement of molten rock in the mantle driven by temperature differences between the lower and upper mantle
Mid-ocean ridge
An underwater mountain chain that is normally found along a divergent plate boundary. A rift runs along its spine where new sea floor is created
