Earth ScienceEarth Science

Plate tectonicsPlate tectonics

Why have all the mountains not worn away by now?

Mt. Everest- it’s still getting bigger!

Plate MovementsPlate Movements• There are two types of crust:• OCEANIC and• CONTINENTAL

–If you pushed these two types of plates together,

which do you think would go under, and which

would go over?

• The faster moving, denser one would go under.• But which is which?

The PlatesThe Plates

• Oceanic Plates are usually denser, darker and below sea level.• So Continental plates must be….?

Where are the Plates?Where are the Plates?

• There are 7 MASSIVE plates

• 10 MEDIUM size plates

• And about 60 TINY ones. Can you spot them?

Types of MovementsTypes of Movements

• Diverging- also known as “Constructive Boundaries”• Converging- also known as “Destructive Boundaries”

Types of Plate BoundariesTypes of Plate Boundaries• What is an example of a Constructive Boundary?• That’s right- Seafloor Spreading- lava comes out of

the seafloor and then cools to form new crust,

pushing the plates apart.• There is a country where this can be seen, what is it?• Well done if you guessed Iceland!!

Types of Plate BoundariesTypes of Plate Boundaries

ICELAND:It’s growing 2 to 5cm wider per year!!

Types of Plate BoundariesTypes of Plate Boundaries

• What is an example of a Destructive Boundary?• Remember, they are the same thing as Converging

Boundaries!• See if you can guess from the next slide…

Types of MovementsTypes of Movements

What usually happens at Converging Boundaries?

Types of MovementsTypes of Movements• What usually happens at Converging Boundaries?

• A convergence is a kind of “crash”. So when two

things crash, either- • One goes under, the other goes over (this happens

if they are different densities; or if they are the

same density- • They “mash up” as the impact squashes them-

makes mountains!

Destructive BoundariesDestructive Boundaries• Ocean crust is

forced under the

Continental

crust, into the

Asthenosphere.• This is known

as• SUBDUCTION

So the Earth must be growing?So the Earth must be growing?• Dense heavy oceanic

crust can be subducted below less denser continental crust.

• The friction melts rock• This magma rises

through the crust to form new volcanoes

• This is happening in South America (The Andes)

• The Mariana Trench is the deepest ocean discovered- weird fish!

Or.. Continents Collide!Or.. Continents Collide!

• Eventually when plates move together the continental crust collides

• The heat and pressure make metamorphic rock

• It also pushes and folds the rocks into high mountains

• The Himalayas rise to 8848m and are still growing today

Transform BoundariesTransform Boundaries

• Two plates sliding past each other.

• They move slowly, gripping each other, until the pressure builds up…

• They suddeny slip past each other, QUICKLY

• They’re not usually one crack, but many.

• New Zealand, Japan, California