L3 - When two plates meet Flashcards
Divergent plate boundary - direction of movement; result of movement
Move apart
Volcanoes and small earthquakes
Conservative plate boundary - direction of movement; result of movement
Move side by side, in the same or opposite direction
Earthquake
Two types of convergent plate boundary movement
Subduction
Collision
Convergent subduction - direction of movement; result of movement
One plate under the other
Earthquake and volcano
Convergent collision plate boundary - direction of movement; result of movement
‘Head on collision’, come together
Earthquakes
What happens when an oceanic plate and a continental plate converge?
The oceanic plate subducts under the less dense continental plate into the asthenosphere. (subduction)
Leads to a trench forming
Temp. and pressure increase releasing water and asthenospheric impurities (melts and is called magma)
Composite volcano forms
Is subduction a smooth process?
No, the friction between the plates causes them to stick and pressure builds up in the subduction zone, if the plates slip an earthquake may occur as the pressure is released.
What happens when 2 continental plates converge?
They cannot subduct, they collide (collision)
The rock along the boundary crumples forming fold mountains
There is no subduction zone so no volcanoes are formed.
Major earthquakes can occur
What causes divergent plate boundaries?
Convection currents
What happens when two plates diverge?
Pressure reduces and heat rises, magma rises to fill the rift valley (gap), this then cools forming a new oceanic lithosphere.
Shield volcanoes form and a chain of them form along the boundary - called a mid-oceanic ridge
Earthquakes aren’t severe.
What happens at conservative plate boundaries?
Plates move past each other, causing a fault (e.g. San Andreas fault line
The plates tend to get stuck, then pressure builds up, the plates jerk and cause earthquakes
