L3 When two plates meet Flashcards
Subduction
The ‘old’ oceanic crust subducts below the ‘really old’ continental crust
The oceanic crust is destroyed as it melts back into the mantle
Magma called andesite (think Andes) is made
Sea water is dragged down with the ocean plate
Magma is less dense – so it rises, through the continental crust
Water erupts as steam – volcanoes van be very explosive
What’s the Earth broken up into?
The Earth’s crust is broken up into a number of major and minor plates
What is the area where two plate boundaries meet called?
Plate boundary
What happens along or near the plate boundaries?
Majority of volcanoes and earthquakes
What are the three main types of plate boundary?
convergent, divergent and conservative
What can the convergent boundariesbe further divided into?
collision and subduction boundaries, depending on the types of plates involved (continental/oceanic)
Where are the volcanoes found?
Volcanoes are found only at divergent and convergent subduction boundaries, where there is process for the magma to move up through the crust to the surface.
Where else can the volcanoes be found other than the boundaries
volcanoes can be found at hotspots, where plumes of rising magma “punch through” the crust
Example of a conservative plate
4 points
San Andreas fault in California, USA. North American and Pacific plates sliding past each other.
Small earthquakes up to the magnitude of 8.5.
No Volcanoes.
Example of a divergent plate
6 points
Iceland, on the mid- Atlantic ridge.
The Eurasian and Oceanic plates pulling apart.
Earthquake goes up to 5.0-6.0 on the richer scale.
Volcanoes are not very explosive and dangerous.
Occurs in the cracks of the crust.
Erupt balsalt lava at 12000 degrees.
Example of a convergent plate
8 points
Andes mountains in Peru and Chile.
Nazca Oceanic plate is subducted under the South American continental plate.
Very destructive and has a magnitude of 9.5.
Tsunami can form.
Very explosive and destructive volcanoes.
Steep sided and cone shaped.
Erupt andesite lava at 900-1000 degrees.
Collision Zone
5 points
Himalayas.
Formed when the Indian plate and the Eurasian plate collide into each other.
Destructive earthquakes, magnitude of 9.0
Landslides are triggered.
Volcanoes are very rare.
What happens at Convergent plate boundaries?
When an Oceanic plate meets with a Continental plate. The denser plate goes under the other plate, this is called Subduction.
This forms a deep trench.
As it subducts it would lead to high pressure and temperature. Forcing it to release water and other impurities into the athenosphere.
What happens at the Divergent plate boundary?
This often happens underwater.
As the plates break apart, rising heat and reduction in pressure causes the athenosphere to melt which forms magma.
The magma rises to fill the gaps in between the plates.
It cools to form a new oceanic lithosphere.
As the process repeats a chain of volcanoes is made.
What happens at the Conservative plate boundary?
The current causes the plates to slide past each other.
This occurs whilst the pressure starts to build up. If the plate suddenly jerks past the other. It would cause an earthquake.
