Plate tectonics Flashcards
what is plate tectonic theory?
-The lithosphere is broken up into large slabs of rock called tectonic plates.
-These plates move between convection currents, which pull and push the plates in different directions.
what are convection currents?
These are caused when the less dense magma rises, cools and then sinks. The edges of where plates meet are called plate boundaries or plate margins.
what is the formation of convection currents?
1) heat from the inner core convects through the mantle into the atmosphere.
2) hot magma rises because it becomes less dense with heat (the particles spread out)
3) magma is cooler at the top as it is further away from the heat source, becomes more dense and sinks back down.
4) cooler magma is reheated and begins to rise again, creating a loop called a convection current.
what are the different plate boundaries?
At plate boundaries, different plates can either move towards each other (destructive) move away from each other (constructive or parallel to each other (conservative)
what are the three type of destructive plate boundaries?
1) continental and oceanic
2) oceanic and oceanic
3) continental and continental
destructive- continental and oceanic
-denser oceanic plate subducts beneath the continental, leaving a deep ocean ridge.
-fold mountain occur when sediment is pushed upwards during subduction.
-oceanic crust is melted and subducts beneath atmosphere
-extra magma created cause pressure build up
-pressurised magma forced through weak points of the continental
-explosive, high pressure volcanoes erupt through the continental plate- (COMPOSITE VOLCANO)
destructive- oceanic and oceanic
heavier plate subducts beneath the less dense plate, leaving an ocean trench. fold mountain will also occur.
- built up pressure causes underwater volcanoes bursting through oceanic plate.
-lava cools and creates new land called island arcs.
destructive- continental and continental
both plates are not as dense as the oceanic plate so lots of pressure builds. ancient oceanic crust is subjected slightly, there is no subduction of the continental crust.
-pile up of continental crust on top of lithosphere due to pressure between plates.
-fold mountains formed from piles of continental crust.
what are significant landforms of destructive plate boundaries?
- composite volcanoes
-island arcs
-fold mountains
underwater volcanoes
-ocean trench
what are the 2 types of constructive plate boundaries?
-oceanic and oceanic
-continental to continental
constuctive- oceanic and oceanic
-magma rises in between the gap left by the two plates separating, forming new land when it cools.
-less explosive underwater volcanoes formed as magma rises.
-new land forming on the ocean floor by lava filling the gaps is known as sea floor spreading.
what is the evidence of sea floor spreading?
-Theorised by harry hess
- As the new rock is formed and cools the magnetic grains within the rock align with the magnetic poles.
- our poles switch periodically
-each time these switch the new rocks being formed at plate boundaries align in the opposite direction to the older rock.
- on the ocean floor, either side of the constructive boundaries, there are systematic bands of rock with alternating bands of magnetic polarity. this is evident in sea floor spreading.
constructive- continental to continental
- any land in the middle of the separation is forced apart, causing a rift valley.
-volcanoes form where the magma rises. - eventually the gap will most likely fill with water and separate completely from the main island
-the lifted areas of the rocks are known as horts whereas the valley itself is known as a graden.
what are the processes influencing how convergent boundaries occur?
1) ridge push- the slope created when the plates move apart has gravity upon it as it is at a higher elevation.
gravity pushes the plates further away, widening the gap (as this movement is influenced by gravity, it is known as gravitational sliding)
2) slab pull- this is when a plate subducts, the plate sinking into the mantle pulls the rest of the plate (slab) with it causing subduction.
what is a conservative plate boundary?
-Between any crust, the parallel plates move in the different directions or at different directions or at different speeds.
-no plates are destroyed so no landforms are created.
-when these plates move a lot of pressure is built up.
-on oceanic crust, this movement can displace a lot of water.
-on continental crust, fault lines can occur where the ground is cracked by the movement.
what are hotspots?
Hotspots area areas of volcanic activity that are not related to plate boundaries. hot magma pulmes from the mantle rise and burn through weaker parts of the crust. this can create volcanoes and islands. The plume stays in the same place but the plates continue to move, which sometimes causes a chain of islands such as Hawaii.
