PLATE BOUNDARIES Flashcards
What are the three main types of plate boundaries?
1) Divergent plate boundaries (divide)
2) Convergent plate boundaries (collide)
3) Transform plate boundaries
What do plates do at divergent/constructive plate boundaries?
Divide/Separate
Why do plates divide at divergent plate boundaries?
Convection currents in the mantle beneath them are moving in opposite directions therefore dragging plates apart.
Example of 2 plates that are dividing:
North American and Eurasian plates.
When plates are pulling apart, what happens to the crust exactly?
It tears and cracks/fissures open up in the crust.
In the case of the North American and Eurasian plates where does the crust tear?
In the middle of the Atlantic Ocean under the sea.
What happens when a tear in the earth’s crust occurs?
Magma from the mantle rises through the gap.
When magma rises through the fissures, what occurs after?
The magma cools quickly and hardens , creating basalt.
What’s the term used to describe plates separating under the sea and creating new sea floor?
Sea floor spreading.
Over time due to the process of sea floor spreading, what can occur?
In and around 130my an underwater mountain range can be created.
When the underwater mountain range occasionally rises above the sea what is it then know as?
Volcanic islands.
The underwater mountain range is known as a …
Mid ocean ridge
Concerning the Eurasian and North American plates, what is their mid-ocean ridge called?
Mid-Atlantic Ridge
For how long does the Mid-Atlantic Ridge run for?
15,000 kms
What’s an example of an island along the Mid-Atlantic Ridge?
Iceland.
How many active volcanoes does Iceland have?
130.
What do plates do at convergent plate boundaries?
Collide.
Why do plates collide at convergent plate boundaries?
As the convection currents in the mantle beneath them are moving towards each other, pulling the plates together.
What are the different types of convergent plate boundaries?
1) Oceanic-oceanic convergence (two oceanic plates collide)
2) Oceanic-continental convergence (oceanic and continental plates collide)
3) Continental-continental convergence (two continental plates collide).
What is an example of two oceanic plates colliding?
The Pacific and Philippine plates.
Oceanic-oceanic convergence leads to the formation of what?
Ocean trenches and volcanic island arcs.
Example of a ocean trench:
The Marianas trench
How deep is the Marianas trench?
11km
What is an example of an oceanic and continental plate colliding?
The Nazca and South American plates.
Oceanic-continental convergence leads to the formation of:
Fold mountains and volcanic activity.
When the oceanic plate and continental plate collide what process occurs and describe it.
Subduction - the heavier plate (oceanic) bends and sinks beneath the lighter plate (continental)
Where does subduction occur at?
At a subduction zone.
The collision of the oceanic and continental plate cause the continental plate to…
Buckle upwards which forms a fold mountain range e.g. the Andes.
When the oceanic plate subducts down into the mantle what happens?
The plate melts due to the high heat of the mantle and it’s destroyed.
When the subducted plate is destroyed what occurs?
Extra magma is created in the mantle. Some of magma may spill out through the overlying continental plate resulting in volcanic activity.
Are the Andes volcanically active?
Yes.
Give an example of a volcanically active mountain in the Andes.
Cotopaxi.
What is an example of two continental plates colliding?
Eurasian and Indo-Australian plates.
What does continental-continental convergence lead to?
Formation of fold mountains e.g. the Himalayas.
What’s the highest peak of the Himalayas and what’s the exact figure?
Mount Everest (8848m)
Does any subduction occur during continental-continental convergence? Why?
Little to no subduction occurs as the plates are similar in weight and thickness.
Since plates don’t move down in c-c convergence what does happen?
An uplift where two plates buckle upwards.
Are the Himalayas volcanically active?
No.
What do plates do at transform plate boundaries?
Slide.
Which way do plates slide in at transform boundaries and what speed do they move in?
The can either move in the same or opposite direction but at different speeds.
Example of two plates sliding in opposite direction:
North American and Caribbean plates.
Example of two plates sliding in the same direction:
North American and Pacific plates.
The line that the plates slide along is called a…
Transform fault line.
Give an example of a transform fault line:
The San Andreas Fault.
How long does the San Andreas Fault run for?
1,300kms
In the San Andreas Fault case which plate moves faster?
The Pacific plate moves faster (5cm per year) than the North American plate (1cm per year).
Is the movement of sliding plates smooth?
No, the plates grind against each other.
When the plates grind against each other, what happens?
They get stuck and lock together for decades with pressure building up over time.
When the sliding plates jolt forward again what happens?
The pressure is released and a violent earthquake occurs.
