Crust
This is 0-70 km thick and can be divided into two types- continental and oceanic. the crust is solid and made out of granite and basalt. it has an average temperature of 10 degrees.
Mantle
This layer is 2900 km thick and is liquid. the temperature is 375 degrees.
Core (inner and outer)
This is the hottest part of the earth at 3000 degrees. the outer core is liquid but the inner part is solid and it is made from iron and nickel ore. it is 3500 km thick.
Oceanic plate
Newer
denser but thinner than continental
can sink (subduct)
can be renewable and destroyed.
Continental
Older
less dense but thicker than oceanic
can’t sink (subduct)
can’t be renewable and destroyed.
Why plates move?
the earth’s core is hotter than the layers above. This heats up the mantle. there is also radioactive particles in the mantle that are decaying giving off heat. the magma nearest to the core is heated and rises to the top of the mantle. as it reaches the top it cools and sinks back down. This creates a circular motion called convection current. there are many convection currents operating in the mantle. at places where two currents are sinking then they will pull plates together into a subduction zone. where the current direction is going up then it will pull plates apart and creates rifts and ridges.
Destructive (subduction) plate boundary
- Plates collides
- Oceanic plate subducts because it is denser.
- Oceanic plate melts to form magma due to heat friction and pressure
- Pressure builds in the magma chamber as more magma is added.
- Volcanic eruption eventually takes place.
Subduction
when an oceanic plate meets a Continental plate.
Destructive (collision) plate boundary.
- Two plates collide (they can’t subduct) because of equal density.
- Plates forced together (crumble) to from mountain Ranges
Constructive plate boundary
- Continental crust pulls away from the other crust.
2. Magma rises to the top and solidifies (fills in) to form new crust.
Conservative plate boundary
- The plates moves along side each other in opposite direction or the same but with different speeds.
- Plates have jagged edges, friction builds.
- Plate stick and slip as pressure builds, which causes an earthquake.
Different landforms
Composite Volcanoes - subduction
Shield Volcanoes - constructive
Fold mountains - collision
Ocean trenches - subduction
Composite
- Composite volcanoes are steep sided volcanoes.
- Significant pressure builds within composite volcanoes and often results in spectacular eruptions.
- Example of composite volcanoes include Mount Pinatubo in the Philippines and Mount Vesuvius in Italy.
- Composite volcanoes are very explosive because the lava is very viscous (thick).
- Composite volcanoes consist of layers of ash and lava.
Composite
- The sticky acidic lave pours slowly down the sides of the cone like toothpaste and cools quickly - this produces the cone’s steep sides.
- Composite volcanoes happen when the lava is acidic( also called felsic). You get these along destructive plate margins. This lava is sticky so it makes steep-sided mountains. Mount Mayon is the Philippines is like this.
Composite
- The viscous magma traps hot gases within it, releasing them suddenly in an eruption. As it was originally oceanic crust, the magma also contains a lot of water which, as stream, increases the pressure in the lava tube. This makes a violent eruption more likely.
- A rock plug may be left from a previous eruption. This can be blown off in the future eruption, producing a hail of ash and rock. the top of the cone might collapse.
Shield
- They consist of many thin layers of rock.
- Shield volcanoes are common in Hawaii and Iceland. They have gentle slopes and are very wide.
- Shield volcanoes are formed when lava is very hot and very runny.
- Shield volcanoes look like an upturned shield.
- Because the magma is not vicious, it releases its gases, preventing a build-up pressure. Eruptions therefore tend not to be explosive.
Shield
- Alternate layers are formed because each eruption first produces rock fragments which are later covered by lava
- Basic lava is runny so it flows quite a way before it cools- this produces wide cones with shallow sides.
- Shield volcanoes form when the lava is basic ( that’s the opposite to acidic; it’s also called Mafic). You get these along constructive plate margins, like in Iceland, and also where there are hot spots, like Mauna Loa in the Hawaiian islands.
Fold Mountains
- Fold mountains are formed when two plates push together (destructive)
- Sediment that builds up in geosynclines in the sea turn into sedimentary rock over thousands of years.
- When the plants push together, this rock is crumpled up and fold into mountains.( e.g. Alps)
Ocean Trenches
Deep ocean trenches are formed offshore at destructive plate margins (subductive zones) where the denser oceanic plates dives beneath the less dense continental plate. these are the deepest parts of the ocean such as the Japanese Trench, the Peru-Chile trench.
The three P’s
- Prediction
- Protection
- Preparation
Prediction
- Trying to forecast when an earthquake might occur- (this didn’t work for the Kobe earthquake)
- You can register fore shocks (before the earthquake) but it does not give you enough time to react.
- A simple way of detecting earthquake is that animals scents earthquake and behave differently.
Protection
- open areas - people can be evacuted
- steel frames- sway during an earthquake
- computer controlled weights to reduce movement.
- foundations sunk into the bedrock
- fire resistance building material
- rubber shock absorbs to absorb tremors.
Preparation
-This involves hospital, emergency services and inhabitants practising for major disasters, including having drills in pubic buildings and a code of practice so that people know what to do to reduce the impact and increase their chances of survival.
