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Plate Boundaries: (Destructive plate boundary: (Associated landforms:…
Plate Boundaries:
Destructive plate boundary:
What happens at the boundary?
Oceanic and continental plates collide
The oceanic plate subducts beneath the continental
The crust returns to the mantle
A subduction zone is created.
Benioff zone: zone of deep earthquakes- where the oceanic is being subducted.
Oceanic crust is older and denser. 0-25 km thick
Made of basaltic rock.
SIMA: Silicon and Magnesium
Continental crust is younger and lighter. 0-75 km thick
made of granitic rock.
SIAL: Silicon and aluminum.
Movement in the boundary:
Slab pull: The motion of the oceanic plate being subducted.
Subduction zone: zone where the two plates are sandwiched upon one another.
Associated landforms:
Hotspots: areas where volcanic isn't linked to tectonic activity.
Magma strings reach the surface and eventually breakthrough (repeatedly)
Ocean trenches: deep layers of ocean floor as the crust subducts.
Young fold mountains: sediment pushed up during plate movement.
Island arcs: string of eruptions off the coast.
Volcanoes: only composite at destructive plate margins
Constructive plate boundary:
What happens at the boundary?
Two plates are moving away from one another creating a gap in the surface
New crust is being created meaning young rock features are found at these boundaries
Can happen with two oceanic plates or continental plates
Oceanic: the seafloor spreads and creates an ocean ridge
Continental: Crust can be stretched causing rift valleys
Movement within the boundary:
Gravitational sliding: The movement of unstable rock
Mid Atlantic ridge: North American and Eurasian plates moving away.
Sliding causes the walls to fall - rock slides
Paleomagnetism: study of the earth's magnetic field
Magma solidifies - the iron rich sediment aligns with magnetic field.
Associated landforms:
Volcanoes: shield volcanoes form because the lava is basaltic and not viscous.
Surtsey: island formed from volcanic eruption 130 m below sea level
Earthquakes: movement of magma in the crust
Can occur at mid-atlantic ridge- has fault lines at right angles. Can cause earthquakes due to lateral movement
Rift valleys: continental crust moves apart
Brittle crust fractures and drops down between parallel faults
African rift valley: associated volcanic activity. Crust is thinner here
Ocean ridges: underwater mountains
Formed by consistent eruptions of basaltic lava
Conservative plate boundary
What happens at the boundary
Two plates slide past one another
Can be sliding past in different directions or the same but different speeds.
No crust is destroyed
Associated landforms:
Earthquakes: shallow and powerful
The richter scale depends on the smoothness of the movement between the plates
The ground ruptures at the spot of the focus
Friction builds up and eventually the plates jolt past one another causing an earthquake
Fault lines: these are cracks in the rock
