Geography Hazards

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Layers of the Earth:
There are 4 layers in the Earth. The most outer layer is the crust.
There are 2 types of crust, which are oceanic and continental. The
oceanic crust is made of an igneous rock called basalt whereas the
continental crust is made up of granite. Granite is less dense than
basalt, which makes the oceanic crust a lot heavier. Also the oceanic
crust is only 6 – 8km thick but the continental crust can be 30 – 50km
thick. The continental crust mainly consists of low density materials
and is therefore a lot lighter than the oceanic crust. As suggested in
their names, the continental crust forms the land and oceanic crust is
found under oceans.
Below the crust is the mantle. This is a semi – liquid layer as it is
made of molten rock (magma, when it rises above the surface it is
called lava). Inside the mantle, convection currents are created as a
result of the heat generated in the inner core. The heat causes the
liquid to heat up, which makes it lighter thus causing it to rise. As
the liquid moves further away from the heat source it cools, becomes
denser and sinks. This is a continuous cycle.
Underneath the mantle, there is the outer core. This is actually a
liquid layer as it is under low pressure. It consists of iron and
nickel and can have temperatures ranging between 4000 and 5000˚C.
The innermost layer is the inner core. This is a solid and has similar
temperatures to the outer core. As it is very deep into the Earth, it
generates a lot of heat. This is the cause of convection currents in
the mantle.
The core as one makes up the Earth’s radius!
Plate Boundaries and Tectonic plates:
Just between the mantle and crust is a layer of tectonic plates. The
movements of these plates control the movement of the crust. When the
convection currents, they can force the plates in certain directions.
Depending on which direction 2 plates are pushed in, determines the
type of plate boundary that is created for that area.
If 2 plates are pushed together and one plate is pushed back into the
Earth, a destructive plate boundary is formed. When the plate
boundaries are pushed together, the oceanic crust is sub-ducted
underneath the continental crust because it is denser. At this plate
boundary, most deadly earthquakes, volcanoes and mountains are formed.
Sometimes when the Oceanic crust is being pushed underneath the
surface, it can stick to the continental crust. When it lets go, large
amounts of pressure and heat are released - resulting in an
If 2 plates are pushed together and both plates are pushed upwards, a
collision plate boundary is formed. At this plate boundary, mountains
form and big earthquakes take place. Even though both plates are
pushed upwards, some parts of the crust fall back into the mantle
(this adds to the molten rock so that when magma is…


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