Geography lesson on 4/3/11

Earth:

Crust - Solid

Mantle - Liquid

Core - Solid

 

 

 

The Plate movement:

The Plates 'floats' on the liquid mantle. As the Earth is spherical, and convection currents occur in all parts of the mantle, plates dragged away from one side will also collide on the other side. This leads to the different types of plate movements all over the Earth's surface.

 

 

Convergent Plate Movement

When two plates move towards each other, they would collide. This is called a convergent plate movement. As the plates collide, some crust is destroyed due to the impact, therefore this convergent boundary is also called a destructive boundary.

When A Continental And Oceanic Plate Collide
When a continental plate and an oceanic plate collide, subduction occurs. The oceanic plate sinks under the continental plate as it is denser. The crust carrying the ocean melts underneath at the subduction zone due to the immense friction and high heat of the magma, which is acidic with higher silican and sulphuric content.

The impact of the collision also causes cracks to form in the crust. The heat and pressure from the mantle forces the acidic magma to rise up these cracks. As the magma continues to rise up the cracks, it escapes onto the surface and solidifies, building up a volcano. Magma on the surface is now known as lava. Thus, an acid lava volcano is formed.
The converging of the oceanic and continental plate also cause deep oceanic trenches and fold mountains to form.

When Two Continental Plates Converge
When two continental plates converge, one plate will be forced only slightly under the other, but no subduction will take place. Thus, the pressing together of two plates will fold the crust and forms what we known as fold mountains.

When Two Oceanic Plates Converge
Similarly, when one oceanic plate converge, the other oceanic plate may subduct beneath the other. However, there is no head-on collision for two oceanic plates. Magma will then rise up to form volcanoes.

 

Divergent Plate Movement

A divergent plate movement occurs when two plates move away from each other. Magma from the mantle underneath the crust to rise up the surface to cool and solidify at the plate boundary. This divergent boundary is considered constructive since new crust is formed.

Divergent takes place at the boundary of the oceanic plates and forms new sea floor. This process is called sea-floor spreading.

As magma rises up to the surface, it piles up and solidifies, slowly forming a long chain of moutains on the ocean floor, called an oceanic ridge.

Volcanoes can also form undersea at these divergent boundaries, they are called submarine volcanoes and have gentle eruptions.

Transform Plate Movement

A transform plate movement is one where two plates slide laterally past each other. However, movement is not smooth due to friction between the rocks of the two plates. Therefore, sometimes the two plates would get 'stuck' and lock together. But since the convection currents of the underlying magma are still dragging the plates, much tension and pressure is built up at the transform boundary. When there is sufficient buildup of pressure, rocks in the plates break and get jerked apart. This results in earthquakes.