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PLATE BOUNDARIES - Coggle Diagram
PLATE BOUNDARIES
CONTRUCTIVE
CONTINENTAL 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 rocks are known as horsts whereas the valley itself is known as a graben.
OCEANIC 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 (as the floor spreads and gets wider).
EVIDENCE OCEANIC AND OCEANIC There is sufficient evidence to prove plate movement, and seafloor spreading (theorised by Harry Hess in the 1940s) provides some of this proof. Paleomagnetism is the study of rocks that show the magnetic fields of the Earth. As new rock is formed and cools the magnetic grains within the rock align with the magnetic poles. Our poles (North and South) 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 constructive plate boundaries, Geologists observed that there are symmetrical bands of rock with alternating bands of magnetic polarity. This is evidence of seafloor spreading.
RIDGE PUSH
The slope created when plates move apart has gravity acting 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).
SLAB PULL
When a plate subducts, the plate sinking into the mantle pulls the rest of the plate (slab) with it, causing further subduction.
PLATE MOVEMENT
OCEANIC Low density of rock, mainly basalt, thin, newly created.
CONTIENETAL – High density of rock, mainly granite, thick, old.
DESITY The density of the plate will determine whether the plate subducts or is forced upwards. This will determine the landscape and hazards the margin is vulnerable to.
MECHANISMS
MANTAL CONVTION Radioactive elements in the core of the Earth decay which produce a lot of thermal energy. This causes the lower mantle to heat up and rise, as the magma rises it cools down and becomes more dense and begins to sink back down to the core. These are convection currents. These convection currents push the plates.
SLAB PULL
Radioactive elements in the core of the Earth decay which produce a lot of thermal energy. This causes the lower mantle to heat up and rise, as the magma rises it cools down and becomes more dense and begins to sink back down to the core. These are convection currents. These convection currents push the plates.
NOT FULLY UNDERSTOOD
It is important to note that tectonic movement isn't fully understood. Previously, convection currents were thought to be the primary cause of plate movement. However, researchers now believe that Slab Pull is the primary mechanism for plate movement; convection currents seem too weak to move massively dense plates.
DESTRUCTIVE
CONTENTAL AND OCEANIC
● Denser oceanic plate subducts below the continental.
● The plate subducting leaves a deep ocean trench.
● The oceanic crust is melted as it subducts into the asthenosphere.
● The extra magma created causes pressure to build up.
● Pressurised magma forces through weak areas in the continental plate
● Explosive, high pressure volcanoes erupt through the continental plate, known as composite volcanoes.
● Fold mountains occur when sediment is pushed upwards during subduction.
OCEANIC AND OCEANIC
● Heavier plate subducts leaving an ocean trench. Fold mountains will also occur.
● Built up pressure causes underwater volcanoes bursting through oceanic plate.
● Lava cools and creates new land called island arcs.
CONTINENTAL AND CONTINENTAL
● Both plates are not as dense as oceanic so lots of pressure builds.
● Ancient oceanic crust is subducted slightly, but there is no subduction of continental crust.
● Pile up of continental crust on top of lithosphere due to pressure between plates
● Fold mountains formed from piles of continental crust.
CONSERVATIVE
CONCERVATIVE
Between any crust, the parallel plates move in 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.
PLATE BOUNDARY
At plate boundaries, different plates can either move towards each other (destructive plate margin), away from each other (constructive plate margin), or parallel to each other (conservative plate margin). Different landforms are created in these different interactions. This spider diagram outlines what landforms and processes occur at the boundaries.