Tectonic Plates

Tectonic Plates

1. The Structure Of the Earth

   • 3. The Outer Core
     • This is made from iron and nickel.
     • This is a liquid.
     • About 2220 kms thick.
   • 1. The Crust
     • This is the hard outer shell.
     • About 8-65 kms thick.
     • Also called the Lithosphere
   • 2. The Mantle
     • This section is often described as molten - neither liquid or solid.
     • In the upper part of this rock is hard but it is soft lower down and runny in other places.
     • It forms about half of the earth as it is about 2900 kms thick.
     • About 3800 degrees.
   • 4. The Inner Core
     • This is made from iron and nickel and is a solid.
     • About 1260 kms thick.
     • Radioactive decay of uranium generates heat making the core 5500 degrees.
     • 3 million times the pressure on the surface.

2. Plate Margins - where two tectonic plates meet.

   • Destructive Plate Margins
     • 1. An oceanic plate and a continental plate collide. As the continental plate moves towards the oceanic plate, land on the edge of the plate gets crumpled up to form fold mountains, like the andes.
     • 2. The oceanic plate is denser than the continental plate, so it sinks beneath the continental plate. This is known as subduction. As the oceanic plea sinks below the continental plate, it creates friction. This friction then causes an earthquake
     • 3. As it sinks down into the mantle, it melts forming magma.
     • 4. It also takes sea water down with it making it less dense than the mantle. This means it will eventually rise up throughout the continental crust and explode at the surface s a volcano.
     • 5. The trapped sea water then turns into steam and then this makes the volcano very explosive. There is not much lava, but there is a lot of ash, steam and gas.
   • Constructive Plate Margins
     • 1. The plates are moving apart. This allows magma from the mantle to rise up to the Earth's surface and make new crust. This process is known as sea floor spreading.
     • 3. The plate movement can cause volcanic eruptions and the friction of the plates moving over the mantle causes earthquakes.
     • In the oceans this produces a mid ocean ridge system (a global range of underwater mountains.)
   • Conservative Plate Margins
     • 1. The two plates are moving past each other in different directions or in the same direction at different speeds.
     • 3. These are rare but very destructive, because they occur close to the Earth's surface.
     • 2. Lithosphere is neither created nor subducted. Earthquakes occur due to friction which locks blocks. The pressure builds upend then it is suddenly released as an earthquake.

3. Two Types Of Crust

   • Oceanic crust
     • 5-10km thick.
     • More dense.
     • Sinks into the mantle when oceanic and continental crust meet.
     • The oldest is only about 180 million years old.
     • Forms constantly at constructive plate margins and is destroyed at destructive plate margins.
   • Continental crust
     • 25-100km thick.
     • Less dense.
     • It doesn't sink
     • it is very old, 3-4 billion years old.
     • New crust isn't formed and it can't be destroyed.

4. Convection Currents

   • As heat rises from the Earth's core, it sets off convection currents in the mantle. The convection currents move about as fast as your fingernails grow, so not fast at all. But it's enough to allow the plates to move. And it's that movement that sets off earthquakes and volcanic eruptions.
   • Where convection currents rise plates more apart.
   • Where convection currents sink plates move together.

5. Volcanoes

   • Composite Volcanoes
     • They are found at destructive plate margins. When the oceanic plate sinks into the mantle and melts, it forms magma. Magma mixed with sea water then rises up through cracks in the earth's crust and erupts at the surface forming volcanoes.
     • Composite volcanoes have steep sides, and are made up of alternate layers of ash and lava.
     • The lava is sticky, so it doesn't flow far. It is also acidic.
     • Eruptions can be violent, expelling steam, ash, lava and rock. But these eruptions are frequent.
   • Shield Volcanoes
     • They are found at constructive plate margins. As the two plates move apart, magma rises up from the mantle. Some magma is forced to the surface through a vent forming a volcano.
     • Shield volcanoes have a wide base and gently sloping sides.
     • The lava is funny and flows a long way. It is also basic.
     • They are frequent eruptions but they are not violent ones.

6. Fold Mountains

   • How are they formed?
     • An example of fold mountains is the Himalayas. The Himalayas lie on a collision zone.
     • 1. Two continental plates are pushing into each other.
     • 2. They both have the same density therefore neither sink. Instead they are pushed upwards forming a flooding effect.
   • Using Fold Mountains - The Himalayas
     • Tourism
       • Advantages
         • Tourism brings in vital money to nepal. Tens and thousands of people rely on trekkers for income.
         • The cost of climbing Mt Everest is around £5000 per group of 7 climbers.
         • It provides needed income for local Nepalese people.
         • A sherpa guide earns £1600 per 60 days.
       • Disadvantages
         • Climbers leave a lot of rubbish and it has now been described as the worlds highest dumping zone.
         • Providing precious electricity and water for local people is hard with loads of tourists.
         • The mountain is now becoming very crowded.
       • Possible Solutions To The Disadvantages
         • Encourage people not to litter by putting up signs. This will help the environment.
         • Have limited people climbing the mountain to prevent over crowing . This will help the environment.
         • Try to limit the amount of tourists by raising the prices so they have less people climbing but still get a decent amount of money. This will help local people.
     • Mining
       • Advantages
         • Minerals are found that they can sell it and make money.
         • Extracting these minerals with develop the country.
       • Disadvantages
         • Mining is dangerous.
         • It is expensive and difficult to start doing.
         • They lose money paying for resources.
       • Possible Solutions To The Disadvantages
         • They could try to make a profit when they buy the resources. This will help the economy.
         • Try to fence off to mining area to local people to prevent injuries. This will help local people.
     • Farming
       • Disadvantages
         • If it floods they won't get any money or food.
         • The soil is thin so crops are often grown on terraces.
         • Deforestation for land to grow the crops.
       • Advantages
         • 35% of The country's GDP
         • To farm things that they can make money off. Selling earns them money.
       • Possible Solutions To The Disadvantages.
         • Use open land so you aren't cutting down trees. This will help the environment.
         • Try to find alternate ways to get money or grow flood resistant crops. This will help local people and the environment.
     • Hydroelectric Power
       • Advantages
         • It is a clean source of water.
         • They can generate a lot of it.
         • It is renewable
       • Disadvantages
         • Land gets flooded because they need to fill the resvoir.
         • It costs a lot of money to build.
       • Possible Solutions To The Disadvantages
         • They could look at cheaper alternatives. This will help the economy.

7. Super Volcanoes

   • What Is A Super Volcano?
     • They are volcanoes capable of erupting on a much bigger scale than a normal volcano.
     • It looks very different as it doesn't have a cone or peak.
     • In a normal volcano, magma flows up from the deep inside the Earth and pours out of the cone. But in a super volcano:
       • 2. The pressure begins to build up, more rock melts and more magma is formed, creating a vast magma chamber.
       • 1. The magma is blocked from reaching the earth's surface.
       • 3. When the pressure becomes too much, the entire surface above the magma chamber is blown away by a huge explosion, forming a caldera.
   • What Would The Impacts Be?
     • It was cause utter devastation. The impacts would be felt all around the world.
     • Magma would be flung 50 km into the atmosphere.
     • Virtually all life up to 1000 km away would be killed by falling ash, lava flows and the force of the explosion.
     • 1000 km cubed of lava would pour out of the volcano. Enough to cover the whole of the USA with a layer 12.5cm thick.
     • The amount of ash and gas thrown up into the atmosphere by the explosion would dramatically reduce the level of radiation from the sun reaching the Earth's surface (global dimming).
     • Society wouldn't survive.
     • Economies would collapse.
     • Crops wouldn't grow.
     • It would trigger a freezing cold volcanic winter across the planet.
     • It would form a huge caldera. A caldera is a depression formed by the collapse of land after a volcanic eruption.
   • The Distribution Of Supervolcanoes
     • There is a group on the west of the North American plate.
     • The majority of them can be found at destructive plate margins.
     • Several of them can be found on destructive plate margins of the pacific plate.
     • They are some that can be found away from plate margins.

8. Earthquakes

   • Measuring Earthquakes
     • The Mercalli scale measures the power and effects of the earthquake, based on what is observed. The scale goes from 1-12 but in roman numerals. For example, I - Most people wouldn't even feel it the earthquake, IV - Most people would feel it and windows would break and XII - Everything would be destroyed (buildings, bridges, railways). The ground would move in waves.
     • The Richter scale measures the strength or magnitude of an earthquake. This is a logarithmic scale. So, for example, a magnitude 6 earthquake is 10 times more powerful than a magnitude 5 earthquake, and 100 times more powerful than one measuring 4. There is no upper limit to this scale.
   • What Causes Earthquakes?
     • 1. Earthquakes occur at plate margins because of friction. The plates try to move and get stuck.
     • 2. Pressure builds up as the plates keep trying to move. If the pressure is released slowly, we will hardly notice the movement. But if the is released suddenly, it can send out huge pulses of energy and therefore causing the Earth's surface to move.
     • 3. This release causes the Earthquake.
     • They occur at 4 different types of plate margins, which are destructive margins, collision zones, constructive margins and conservative margins.
   • Key Words
     • Seismic waves - elastic waves in the Earth produced by earthquakes.
     • Focus - the location of where the earthquake begins underground.
     • Epicentre - the point on the Earth's surface where the earthquake starts. It is directly above the focus.