The Challenge of Natural Hazards - AQA GCSE Geography

Earthquakes occur where plates pull apart, move together or slide past each other.
1. Plate Margin Types
  1. Constructive
    1. The upper mantle melts, meaning magma rises, plates move apart and magma cools and solidifies. Forms a new oceanic plate, most of the magma doesn't reach the surface, pushes the crust to perform ridge pull/ lift features. Where it erupts on surface shield volcanoes are formed, eg. through Iceland
  2. Conservative
    1. This is where plates move parallel to each other. Pressure builds up as the plates are pulled along and subducted. As plates move, friction causes them to get stuck so pressure continues to build up, which is eventually released, triggering an earthquake. No gap between crust and mantle so magma cannot be formed. Eg. San Andreas Fault Line
  3. Destructive
    1. Plates move towards each other and collide. could be a collision between continental+continental crust, or continental and oceanic crusts. when cont+cont, mountains are formed. When cont+oceanic plates collide, it is subducted into the mantle, causing pressure to be built, which will eventually be released and earthquakes occur. Create compositite cone volcanoes.
Tectonic Hazards
1. Effects of an Earthquake
  1. Worsened by: High Population Denisty, LIC, Near Danger (Nuclear Power Station, eg) Relief of land, Time of Day, Preparation.
Weather Hazards
1. Tropical Storms
  1. Form between 5-15˚ North and South of the Equator, over warm, tropical oceans around 26.5-27˚C, and low wind shear - wind remains constant.
  2. Areas of low pressure (where air rises) with wind speeds in excess of 120km/h.
  3. Structure includes convection cells, where warm air rises, travels away from centre and falls as it cools.
    1. The centre is called the Eye of the Storm, very calm and wind speed is reduced, surrounded by eye wall. Eye wall is the most intense part of the storm.
      1. Passage can be misleading, people may think the storm is over when they are in the centre, dangerous.
  4. Responses to Tropical Storms - CASE STUDY - Typhoon Haiyan
    2. Typhoon Haiyan was in the Philippines, and considered at Super Typhoon, highest winds of 195mph.
2. Extreme Weather in the UK
  1. There is evidence to show UK weather is changing, for example temperatures have increased by around 1˚C, and there have been 6 years where rainfall is well above average. It is predicted that temperatures will raise a further 2-3˚C in the 21st century, which may also be cooled by melting ice caps cooling the Atlantic Ocean.
  2. CASE STUDY - The Somerset Levels
  3. Other examples of extreme events in the UK are thunderstorms and flash floods, with Storm Desmond, Cumbria, 2014, draught and extreme heat in the European Heatwave, 2003, heavy snow and extreme cold, in the winter of 2010-11 and strong winds, with ex-hurricane Ophelia, 2017.
3. Climate Change
  1. Causes
    1. Solar Outputs - Measured by sunspots, caused by magnetic activity inside the sun. Has been recorded since 1900, not much change, so cannot be responsible for climate change since 1970s.
    2. Deforestation - if it continues at current rate, world's forests could disappear within hundreds of years. During photosynthesis, trees absorb CO2 which reduces emissions into the atmosphere. When they are cut down, the CO2 is released, and less trees means less CO2 absorbed.
    3. Agriculture - 20% of global greenhouse emissions, cattle produce it during digestion and produced by rice.
    4. Fossil Fuels - Account for over 50% of emissions. Burning the fuels releases carbon dioxide. Fossil fuels are used in most things, from cars to homes and to producing electricity in power stations. Population growth means more fossil fuels are required.
    5. Orbital Changes - The distribution of the Sun's energy on Earth changes based on the Earth's orbit. It is an ellipse, which changes shape every 100,000 years, so the distance between the Sun and the Earth also changes. The Earth's axis is also tilted on an angle, which changes due to gravitational pull of the moon, when the angle of tilt increases, summer gets warmer and winter gets colder. It moves back and forth every 41,000 years.
    6. Volcanic Activity - Volcanic Eruptions can cause temporary climate change. For example, in 1991 Mount Pinatubo erupted, which released 20 million tonnes of SO2 into the atmosphere. This cooled global temperatures by around 0.5˚C, due to SO2 reflecting the sunlight away.

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The Challenge of Natural Hazards - AQA GCSE Geography

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