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Tectonics Assessment
Term | Definition |
---|---|
lithosphere | the outermost part of the Earth including the crust and upper mantle |
convergent | two plates move towards each other, continental vs continental plates produce Fold Mountains eg. the Himalayas. Where oceanic vs continental plates, Subduction Zones are formed |
divergent | two plates move away from each other, continental vs continental plates produce Rift Valleys eg. East African Rift Valley. Where oceanic vs oceanic plates Oceanic Ridges form eg. Mid-Atlantic Ridge. |
subduction | oceanic vs continental plates move towards each other, due to the difference in density, the more dense oceanic plate sinks and is forced beneath the less dense continental plate |
transform | two plates slide past one another, typically with a stick-slip motion - this produces seismic activity and earthquakes |
asthenosphere | the ductile part of the earth just below the lithosphere, including the upper mantle |
igneous | rocks such as Granite (below the surface) and Basalt (on the surface) formed from cooled magma |
sedimentary | rocks formed by the deposition of layers of eroded 'sediments' under various conditions eg. Limestone, Sandstone and Shale |
metamorphic | sedimentary or igneous rocks altered under intense heat or pressure eg. Marble and Slate |
continental | plates are between 20-80 km thick and relatively less dense |
oceanic | plates are thinner, around 10 km thick and relatively dense |
hotspots | These are super heated areas of magma within the mantle which cause magma to break through the crust eg. Hawaiian Islands in the middle of the Pacific plate. |
shield | found at constructive, divergent margins, produced by flows of fluid lava which forms gently sloping, low profile cones |
composite | found at destructive, convergent margins, produced by layers of viscous lava and ash which form steep sloped, tall cones |
cinder | found close to subduction zones, these are simply produced by layer upon layer of cooled 'blobs' or lava to form a circular or oval cone |
fold | can be defined as a bend in rock that is the response to compressional forces |
fault | can be defined as the displacement of once connected blocks of rock along a fault plane |
epicentre | the point on the Earth surface directly above the focus |
focus | There is a sudden movement within the crust or mantle, and concentric shock waves move out from that point |
p-waves | They are high frequency, short-wavelength, longitudinal waves which can pass through both solids and liquids. The ground is forced to move forwards and backwards as it is compressed and decompressed. |
s-waves | They move in all directions away from their source, at speeds which depend upon the density of the rocks through which they are moving. They cannot move through liquids |
l-waves | similar to that of waves in the sea. The ground is made to move in a circular motion, causing it to rise and fall as visible waves move across the ground |
tsunami | giant waves which result from underwater earthquakes or landslides |
lahar | mudflow made up of volcanic debris |
pyroclastic flow | super heated explosion of gas, ash and rock |
lava flow | river of molten rock |