Geography Restless Earth

The Earth is made up of different layers
1. 1. Continental crust (Granite) and oceanic crust(Basalt) are both solid and can reach to 900°C
  2. asthenosphere (peridotites) is partially molten and it is between 100-1600°c
  3. Mantle (silica- based minerals) is solid and is between 1600-4000°c
  4. Outer Core (iron/nickel) is a very dense liquid and is between 4000-5000°C
  5. Inner core (iron/nickel) is a very dense solid and is between 4000-5000°C
The two types of crust
1. Continental crust - Makes up most of the land area of the earth. It is dominated by rocks that cooled below the surface, such as granite. It is between 25 km and 80km thick
2. Oceanic crust is much thinner, between 6kn and 8km. It is made up of rocks like basalt
Convection Currents
1. High temperatures in the core create rising limbs of material in the mantle, called convection currents
2. Some of the material moves in sheets creating movement in the crust above it
3. In other places in rises in columns, creating hotspots
Different plate boundries
1. Constructive Margins are formed by rising magma splitting up continental crust and forming new oceans. An example of this is where the Eurasian plate is separating slowly from the North-American plate.
2. Destructive margins are formed when oceanic plates collide with continental plates. the oceanic plate sinks beneath the continental plate. This is called subduction and it creates a very deep ocean trenches near the line of contact. Some of the lightweight materials in the oceanic plate begin to melt because of the hotter temperature in the mantle and begin to rise to the surface to form volcanoes An example of this is where the South American plate meets the Nazca Plate
3. Conservative margins are formed when plates slide past each other or move in the same direction but at different speeds. No crust is formed or destroyed, and volcanoes are not formed. However great strain builds up along the junction, with sudden lurches along the fault. Meaning earthquakes are frequent and often large. An example of this is the San andreas fault
Impact of a hazard
1. The size of the event
2. Vurnilability of population
3. How prepared the population are
Volcanoes
1. Composite volcanoes are steep-sided which takes up a small area. It has alternate layers of ash and lava. the magma/lava is very viscous and sticky. iThey erupt very infrequently and sometimes very unpredictable. Pressure builds up over tmie. An example would be Mt Pinatubo (Philippines)
2. Shield volcanoes are gentle sloped (like a shield) which take up a large area. The magma is very fluid and flows quickly. They erupt very frequently but are generally gentle eruptions. An example would be Mauna Loa (Hawaii, USA)
3. Volcanoes can be active, dormant or extinct
Earthquakes
1. A number of factors control the severity of an earthquake.
  1. The magnitude of the earthquake on the Richter scale
  2. The depth (shallow earthquakes are more destructive)
2. The impact of earthquakes varies according to:
  1. The time of the day
  2. The distance from the epicentre
  3. The level of preparedness
  4. The quality of the emergency services
3. Primary impants - the immedediate effect of an earthquake on property and people. For earthquakes this is the people killed as a result of the shaking and property destruction
4. Secondary impacts - the impact on property and people of an event after it has finished. Lack of shelter and basic supplies, as well as fires, are frequent secondary effects
Predicting natural disasters
1. Volcanic eruptions and tsunamis can be predicted if the right equipment is used
2. Gas emissions, earth tremors and "bulging" of a volcano's flanks can be measured and used to predict eruptions
3. In 1991 about 120,000 people were evacuated from the area around Mt Pinatubo before it erupted
4. Tsunami warning sirens can be used to evacuate people from coasts before a tsunami wave hits
5. Earthquakes cannot be predicted. However being prepared can minimise damage
  1. Emergancy plans
  2. Well trained ad funded emergency services.
  3. Warning systems
  4. Evacuation routes

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Geography Restless Earth

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