Revision on the restless earth

Revision Time:

Inside the Earth

The earth's crust is split into a series of plates.

The places where plates meet are called plate boundaries.

These plates float on the heavy molten rock of the mantle.

Continental drift means that the continents of the world are carried along by the plates beneath them.

Plates can collide and seperate.

The Plates: Eurasian Plate African Plate Pacific Plate Nazca Plate Australian Plate

When Plates collide

Fold mountains are formed Earthquakes occur

When plates separate

Volcanic islands, volcanic mountains and mid ocean ridges are formed.

Folding and fold mountains

Fold mountains are created when two plates collide. When the plates compress ( push together) the earths crust

begins to arch upwards.

Young fold mountains include the Alps and the Rocky mountains,these were formed about 35million years ago.

Ireland's fold mountains are very old and tend to be flat. They were formed 250 million years ago.

Earthquakes

Earthquakes happen when two plates collide or slip past one another .

When the plates compress ( crush together) cracks form in the earths crust. The area of compression is called the focus.

The focus sends out shock waves through the crust, reaching the surface.

The area of the surface hit by the worst shock wave is called the epicentre.

The epicentre is the most dangerous area of an earthquake. A seismograph measures the earthquakes strength. Earthquakes are rated on the Richter Scale

Earthquakes can cause buildings to collapse, roads to crack, mudslides and tsunamis.

Volcanic Activity

Where plates seperate or collide the earths crust cracks and lets through hot liquid rock called magma.

The magma forces its way up through a long hole in the mantle known as a vent

Once the magma hits the earths surface it is now called lava.

When plates seperate the lava may form ridges in the earths surface known as mid ocean ridges.

The most famous ridge is the Mid Atlantic Ridge.

The Mid Atlantic Ridge

The Mid Atlantic Ridge was created when the Eurasian and the American Plates seperated.

The Mid Atlantic Ridge starts at the top of the Atlantic Ocean and runs all the way through down to the bottom.

Iceland is a volcanic Island on the Mid Atlantic Ridge. Famous volcano's in Iceland include Mount Krafla and the

island of Surtsey.

The formation of a volcano:

When the magma reaches the top of the vent, it bursts through the earth's surface.

Lava, ash and mud explode from the surface. The hot lava then flows and spreads out destroying the land

around it. When the lava cools and hardens it becomes cone shaped

and eventually creates a volcanic mountain.

Volcanos can be active, dormant or extinct. Active : erupts regularly Dormant: has not erupted for along time Extinct: has not erupted in historic times.

The Pacific Ring of Fire

This is an area in the Pacific Ocean where there are huge amounts of volcanos and earthquakes.

There have also been numerous tsunamis in and around the ring.

Best of luck in the test