Tectonic Plates Flashcards
What has the plate tectonic theory shown
Plate tectonic theory has shown that the earth crust is not a solid mass but is split into smaller crystal plates which ‘float’ on the semi-molten upper mantle
What is the theory of plate tectonics
The movement of the plates, and the activity inside the Earth, is called the theory of plate tectonics.
State the processes in which plates move
Convection currents
Slab Pull
Ridge Push
What is a convection current
A convection current is the movement within the Earth’s mantle caused by the heat of the core.
Explain how convection currents cause plates to move
As the semi-molten rock in the mantle is heated it becomes less dense than its surroundings and rises. As it reaches the crust above, it spreads out carrying the plates above with it. As the semi-molten rock then cools, it gradually sinks back down to be re-heated
Explain how ridge push cause plates to move
At constructive boundaries, ocean ridges form high above the ocean floor.
Beneath ocean ridges the mantle melts; the molten magma rises as the plates move apart and cools down to form new plate material.
As the lithosphere cools, it becomes denser and starts to slide down, away from the ridge, which causes plates to move away from one another. This is called ridge push.
Explain how slab pull cause plates to move
At destructive boundaries, the denser plate sinks back into the mantle under the influence of gravity, which pulls the rest of the plate along behind it. This is called slab pull.
What is slab pull
Slab pull occurs when older, denser tectonic plate sink into the mantle, pulling newer and less dense sections of plate along behind
When does ridge push only happen
Ridge push occurs at constructive plate boundaries
When does slab pull only occur
Slab Pull occurs at only destructive plate boundaries
When do convection currents occur
Convection currents occur at constructive, destructive and conservative plate boundaries (it is the way plate move more generally)
Name types of plate tectonics
Types of tectonic plate
Destructive plate boundary
Constructive plate boundary
Conservative Plate boundary
Collision plate boundary (type of destructive)
Which plate boundaries move the quickest
Destructive plate margins move quicker than constructive and conservative plate margins
What happens at destructive plate boundaries
A destructive plate boundary is when oceanic crust moves towards continental crust. As the oceanic crust is denser (heavier), it is subducted (forced downwards).
Give an example of destructive plate boundaries
An example of destructive plate boundary: example the Nazca Plate moving towards the South American Plate.
What can destructive plate boundaries cause
The force and pressure from the oceanic plate being subducted can trigger earthquakes.
The heat and friction causes the crust to melt in the mantle, turning the rock into magma. A pool of magma forms. The hot magma tries to rise through the cracks in the curst called vents. The magma (called lava when it reaches the surface) erupts, forming a volcano.
to the surface, which can form a composite volcano.
What landforms are associated with destructive plate boundaries. And how. Examples?
Ocean Trench
When an oceanic plate is subducted (forced under) a continental plate at a destructive boundary, a deep ocean trench is formed at the edge of the continental plate.
An example includes the Pacific Plate subducting under the Mariana Plate forming the Mariana Trench, which is the deepest point of all of the world’s oceans.
What is subduction
Subduction occurs when one crustal plate is forced beneath the other
What happens at constructive plate boundaries
A constructive boundary is where two plates move apart,
What can constructive plate boundaries cause
As a ‘gap’ appears between the two plates moving apart, lava can easily escape either in the form of a gentle eruption (shield volcano) or as a lava flow.
A constructive boundary is where two plates move apart. The movement of plates over the mantle can cause earthquakes
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- tension builds along the cracks in the plates as they move away from each other
at constructive plate boundaries, the magma rises up into the gap created by the plates moving apart, forming a volcano.
Give an example of constructive plate boundary
An example of a constructive plate boundary is the North American Plate moving away from the Eurasian Plate.
Explain how a constructive plate boundaries create new land
A constructive boundary is when two plates move apart. As a ‘gap’ appears between the two plates, lava can easily escape either in the form of a gentle eruption (volcano) or as a lava flow. The lava creates new oceanic crust and forms a mid-ocean ridge
What landforms are created at constructive plate boundaries
Mid-Ocean ridge
An mid-ocean ridge is an underwater mountain range caused by two tectonic plates moving away from each other at constructive plate margins. Magma wells up to fill in the gap, forming new crust. This is known as seafloor spreading as the seafloor grows by a few centimetres each year.
Volcanoes
A constructive boundary is where two plates move apart. As a ‘gap’ appears between the two plates, lava can easily escape either in the form of a gentle eruption (volcano) or as a lava flow.
Rift valleys
here two continental plates are moving apart, a rift valley can form. They are narrow, long landforms with steep sides and a flat floor.
The brittle continental crust fractures as sections of it move apart. As the plates move away from one another, the floor of the valley sinks lower, leaving a valley behind
Give an example of mid-ocean ridges and where in the world
An example of a Mid-ocean ridge is the Mid-Atlantic Ridge is found where the North American Plate is moving away from the Eurasian Plate.
Give an example of rift valley and where in the world
An example of a rift valley is the African Rift valley in East Africa
What happens at conservative plate boundaries
At conservative plate boundaries, two plates try to slide slowly past one another.
Two plates are moving sideways past each other, or are moving in the same direction but at different speeds
Crust isnt created or destroyed
Give an example of conservative plate boundaries in the world
Example of conservative plate boundaries are the North American and Pacific Plates.
San Andreas Fault - the Pacific plate and the North American plate are moving in the same direction but at different speeds.
How can an earthquake occur at conservative plate boundaries
When the two plates stick, as they do often along the San Andreas Fault on California, pressure builds up. This pressure is then released as an earthquake.
tension builds up when the plates that are grinding past each other get stuck
What type of landform does not form at conservative plate boundaries and why
At constructive plate boundaries volcanoes do not form as the crust is neither created or destroyed here.
What happens at collision plate boundaries
A collision plate boundary is when two continental plates move towards each other. At this plate boundary neither plate is destroyed
Give real world examples of collision plate boundaries
An example of collision plate boundary is the Eurasian and Indo-Australian plates move towards each other, .
What landforms are associated with collision plate boundaries
Fold mountains
At collision plate boundaries, the land between them is pushed upwards or buckled under the force to form high fold mountains, such as the Himalayas.
Can earthquakes occur at collision margins
Earthquakes can occur at collision margins. The force and pressure from the two continental plates being pushed upwards or buckled under can trigger earthquakes.
Describe Global distribution of earthquakes and volcanic
eruptions and their relationship to plate
margins.
Earthquakes occur at all three types of plate margins: constructive, destructive and
conservative.
About 70% of all earthquakes are found in the ‘Ring of Fire’ in the Pacific Ocean.
Volcanoes are found at constructive and destructive plate margins. An exception to this are hot spot volcanoes.
Most volcanoes occur in the ‘Ring of ‘Fire’
