destructive plate boundaries

By Natasha Ann Morrison..

This type of plate boundary can also be called a Convergent Plate

Boundary.

They can occur in one of 3 different situations:Oceanic plate moves towards a continental plateOceanic plate moves towards another oceanic plateContinental plate moves towards another continental plate

Oceanic crust is denser than continental crust. Therefore,

when the two plates meet, the oceanic plate is forced beneath

the continental plate. This is called Subduction.

What happens when an oceanic plate and a continental plate meet?

On the surface, where the 2 meet, a deep trench can be formed.

Deep Trench!

ExampleOff the Western coast of South

America, the Nazca plate is being forced underneath the South

American Plate.

This has led to the formation of the Peru-Chile Trench. It is 8065m

below sea level at its deepest point and is roughly 3700m long.

Peru-Chile Trench

As the oceanic plate descends , heat is generated by the friction of the two

plates meeting. This causes the oceanic plate to melt and turn back into magma

in an area of the subduction zone known as the Benioff zone. The magma rises through the gaps in the continental plate and can form a volcano if it reaches the

Earth’s surface. If the eruptions take place offshore, a line of volcanic islands

can be formed called an island arc.

ExampleThe West Indies in the Carribean are an

example of an island arc. They outline the Northern and Eastern edges of the

Carribean Sea. The area consists of the Antilles, Bahamas and the Lucayan

Archipelago.

Sediment that has accumulated on the continental shelf on the margin of the land mass are deformed by

folding and faulting.

Folding is when rock is bent by pressure and heat, forcing the shape of it to be altered.

Extreme stress and pressure can sometimes cause the rocks to shear along a

plane of weakness creating a fault.

These sediments can be uplifted to form fold mountains.

An example of this these are the Andes along the pacific side of South America.

The Andes are the worlds longest continental mountain range. They are

7000km long and 700km wide, reaching an average height of 4000m

The Andes

Another feature which is common at this fault is an earthquake. This

is caused by the increase in pressure along the line of the

subducting plate.

What happens when an oceanic plate meets an oceanic plate?

When oceanic plates meet, one is forced underneath the other and the processes

of subduction begin. Because two oceanic plates are meeting, this plate

boundary always occurs offshore.Ocean Trenches and Island Arcs are the features associated at this

type of boundary.

ExampleOn the Western side of the Pacific ocean, the Pacific plate is being

subducted underneath the smaller Philippine Plate. A very deep trench has been formed, known as Mariana’s trench and an island arc has also been formed.

This island arc consists of volcanic islands including Guam and the

Marianas, which have been formed by upwelling magma from the Benioff zone.

What happens when a continental plate meets a continental plate?

When two continental plates meet, not much subduction happens,

because they have lower densities than the layers of the Earth beneath them. Instead, as the plates move

towards each other, their edges and the sediments between them are

forced upwards to form fold mountains.

As there is little subduction, there is no volcanic activity, but

earthquakes are common. Material and sediment can also be

forced downwards to form deep mountain roots.

ExampleThe Indo-Australian plate is being

forced northwards into the Eurasian plate. What was once the Sea of Tethys has had sediments forced

upwards into it in large overfolds to form the Himalayas in Asia. The

highest mountain on the planet, Mount Everest (at 8848m), belongs to this mountain range. The Himilayas are

350km wide and 3000km long.

The Himalayas

Thank You for watching Tasha’s presentation..!