Plate tectonics

plate boundaries and structure of earth, volcanoes, earthquakes and prevntion and preparation of them

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Plate boundaries

Tectonic plates are all over the world in narrow belts.

Where ever earthquakes are volcanoes also occur.

Conservative plate: plates push/slide past each other. Lots of pressure builds and causes earthquakes. Eg San Andreas.

Destructive: plates move towards each other and forces upwards so mountains are formed. Eg. Himalayas.

Constructive: Plates move away from each other and magma pushes through. Eg. Mid Atlantic ridge.

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Structure of the Earth.

Inner core: About 4,300 degrees, around 1,216 km thich & is 6, 378 km below the Eath's surface.

Crust: About 0 degrees. It is light. Made up of many elements.

Mantles: About 2,900 km thick. Between 1,000& 3,700 degrees & it is like plastic.

Outer core: Has two sections. About 2,270 km thick. Temp. is between 3,700& 4,300 degrees.

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The Epi- centre is above the focus

Primary effects- Direct result of the earthqauke. Eg buildings collapsing, people being killed or injured, fires start and tsuamis can be triggered by the eathquake.

Secondary effect; Knock on effect from the primary effect. Eg diseases may spread and aftershocks.

Vibrations are plotted on a seismograph.

An earthquake is the release of  built up pressure inside the earth's crust.

The most damage is close to the Epi- Centre.

Earthquakes are measured on the Richter Scale.

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Richter/logarithmic scale; measures the magnitude from seismic waves. Each number on the scale means it is 10 times more powerful than the last one. Eg 5 on the Richter scale is windows smashing and 6 is damage to buildings.

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Earthquake prevention& preparation

People are warned about an earthquake.

They have earthquake drills in earthquake prone countries.

In earthquake prone countries they have earthquake proof buildings so they sway instead of fall down.

They have shelter in case of an emergency.

Some people have emergency kits in their homes.

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Volcanoes are formed when magma reaches the Earth's surface and causes Eruptions& ash.

They occur at destructive& constructive plate coundaries.

Volcanoes are formed by eruptions of lava & ash

Volcanoes are usually cone shaped mountains or hills

When magma reaches the Earth's surface its is called lava. When lave cools it turns into rock.

Some volcanoes are underwater.

Eruption pressure in the chamber forces up the main vent to the crater.Magma is also forced out of the secondary vent.

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Active; erupts often

Dormant; inactive but not extinct

Extinct; not likely to erupt again.

Magma chamber; magma inside the Earth below the volcano

Main vent; outlet for the magma to escape

Secondary vent; smaller outlets which magma escapes

crater; after an eruption blows the top off the volcano

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