The earth's crust is makes up the upper layer of the lithosphere.
The plates that make up this lithosphere can move very slowly every year about a few mm becasue of convection currents in the mantle below the Asthenosphere which is where the lithosphere move upon.
These plates make are broken and are called tectonic plates and meet at plate boundaries. there are two types of plates .. Continental and Oceanic.
The are three types of Plate margins:
- Constructive =
- plates move away
- diverging plates
- magma rises and new crust forms
- Destructive =
- converging plates
- plates move toward each other
- crust is destroyed
- fold mountains, eatrquakes adn volcanos are common.
- plates move in different directions or different speeds
- material isnt gained or lost like others
- volcanos are rare
- earthquakes are common
Earthquakes occur at converging plates .. so ....
- As the two plates push against each other
- one will be pushed under the other
- If the plates get stuck then it causes a lot of strain in the surrounding rocks
- when this tension in the rocks is finally released .. it produces strong shock waves called Seismic waves
- this is called a earthquake
- the shockwaves spread out from the focus which is the starting point of the earthquake
- nearer to the focus the waves are stronger and there will be more damage down.
- the epicentre is directly above the focus point but on the earth's surface.
The Richter Scale
Measured the size and the magnitude of the earthqauke using a seisometer.
- The readings are measured using richter scale for energy released
- the logarithmic scale means if a earthquake is with a score of 5 it means it is 10 times stronger than score 4.
There are three types of volcanos:
- it will never errupt again
- Devil's tower, Wyoming
- it hasn't erupted for 2000 years
- Santorini, Greece
- it has erupted recently and is likely to erupt again.
- Mt.Etha, Sicily Italy
- St Helens USA
Two different kinds of volcanos:
A Composite Volcano (LAVA AND ASH)
- Four different types of substances can be ejected from the vent:
- pieces of rocks as volcanic bombs
- molten rock - magma when it is under the ground and lava when it reaches the surface.
- Once the material has been thrown out at the surface, it cools and hardens forming the volcano from the mixture of ash and lava
- eg. Mt.Etna
more on volcanos
Shield and Dome Volcanoes are made upof lava only
- the lava is alkaline and runny
- it flows quickly and easily
- spreading over large areas forming wide, flat surfaces.
- Mauna Loa (Hawaiian islands)
- the lava is acid and thicker
- it flows more slowly
- hardens quickly to form steep sided features
- eg. Mount St Helens