Rivers and Geology

• Hazards Content


  • Atmospheric Circulation, Ocean currents and high/ low pressure
  • Natural causes of climate change
  • Evidence for natural climate change
  • Human causes of climate change
  • Plate boundaries
  • Volcanoes and Earthquakes
  • Formation of a cyclone
  • Impacts on people
  • Impacts on the environment
  • Physical vulnerability
  • Economic Vulnerability
  • Social Vulnerability
• Atmospheric Circulation


  • Winds are part of the global atmospheric circulation loops (called cells)
  • These loops have warm air rising which creates a low pressure belt and cool air falling which creates a high pressure belt
  • The movement of air within these cells is controlled by heating and cooling
  • There are 3 cells in each hemisphere: Hadley, Ferrel, Polar
• Air Pressure


  • The 'weight' of the air and the force this exerts on the ground
  • Pressure has a big impact on the climatic features of an area
  • There are two types of Air Pressure: High, Low
  • It is air pressure that creates WIND
• Explain how global atmospheric circulation determines the location of high rainfall (low pressure) areas


  You may use a diagram to help your answer
• Ocean Currents


  • Large scale movements of water that transfer heat energy from warmer to cooler regions
  • Surface currents are caused by winds and help transfer heat away from the Equator
  • An example is the Gulf Stream that brings warm water from the Caribbean and keeps Western Europe warmer than it would be
• Explain one role of ocean currents

  1. Movement / redistribution of heat energy to regulate uneven global temperatures / high temperatures at the equator / moderate colder temperatures away from the Equator (UK / North Atlantic Drift)

  2. Counteract extreme temperatures at the equator due to uneven distribution of solar radiation at the Earth's surface
• Natural causes of climate change

  • Volcanic Eruptions
  • Solar Output and sun spots
  • Orbital Changes
  • Asteroids
• Volcanic Eruptions


  • Big volcanic eruptions can change the Earth's climate
  • Small eruptions have no effect – the eruption needs to be very large and explosive
  • Volcanic eruptions produce ash and sulphur dioxide gas
  • If the ash and gas rise high enough, they will be spread around the Earth in the stratosphere by high level winds
  • The blanket of ash and gas will stop some sunlight reaching the Earth's surface
  • Instead, the sunlight is reflected off the ash and gas, back into space
  • This cools the planet and lowers the average temperature
• Volcanic eruptions


  • Mount Pinatubo in the Philippines erupted in 1991, releasing 17 million tonnes of sulphur dioxide
  • Mount Pinatubo was very small-scale compared to the 1815 eruption of Tambora in Indonesia, the biggest eruption in human history
• Sunspot theory - solar output


  • The Sun's output is not constant
  • It changes in short cycles of about 11 years, and possibly in longer cycles of several hundred years
  • Lots of spots mean more solar energy being fired out from the sun towards Earth
  • Cooler periods, such as the Little Ice Age, and warmer periods, such as the Medieval Warm Period, may have been caused by changes in sunspot activity (solar output being reduced)
  • The Maunder Minimum was a period of reduced solar activity between 1645 and 1715 which coincided with the Little Ice Age
• Orbital theory


  • Orbital changes are variations in the way the Earth moves round the sun
  • Cold glacial periods and ice ages were 5-6°C colder than today
  • Some interglacials were 2-3°C warmer than today
  • Stretch (also known as eccentricity) the path of the Earth's orbit around the sun changes from an almost perfect circle to an ellipse (an oval) and back again every 96 000 years
  • Tilt- the Earth's axis is tilted at an angle as it orbits the sun. This tilt changes over a cycle of about 41 000 years
  • The Earth's axis wobbles (precession), like a spinning top about to fall over on a cycle of 22 000 years
  • These three changes alter the amount of sunlight the Earth receives and where sunlight falls on the Earth's surface
  • On timescales of thousands of years, the changes would be enough to start an ice age, or end one
• Asteroid Collisions


  • Asteroids hitting the Earth's surface can throw up huge amounts of dust into the atmosphere
  • These particles prevent the Sun's energy from reaching the Earth's surface so global temperatures fall (possibly for several years)
  • Some scientists believe that an asteroid collision caused a period of global cooling (the Younger Dryas) around 12 000 years ago
• Tree Rings


  • Most Trees produce one ring within their trunks every year
  • The thickness of the ring depends on the climate, when the ring was formed
  • When it is warmer the rings are thicker
  • Scientists take cores through tree trunks then date each ring by counting them back from when the core was taken
  • By looking at the thickness of the rings they can see what the climate was like each year
  • It is a bit like a trees individual barcode
• Ice Cores


  • Ice sheets are made up of layers of ice- one layer is formed each year
  • Scientists drill into ice sheets to get long cores of ice
  • By analysing the gases (e.g. carbon dioxide) trapped in the layers of ice, they can tell what the temperature was each year
  • The Vostok Ice Core from Antarctica shows the temperature changes over the last 400, 000 years
• Historical Records

  • Since the 1850s global temperatures have been measured accurately using thermometers
  • Historical records (diaries and paintings) can extend the record of climate change further back
  • Historical diaries- show what the climate was like in the past by giving the number of days of rain/ snow and dates of harvests (early harvest suggests warmer weather)
  • Paintings of fairs and markets on frozen rivers show that winters in Europe were regularly much colder 500 years ago than they are now
• Medieval Warm Period


  • A period of warming between 900 and 1300
  • Harvest records show that England was warm enough to grow lots of grapes
  • Tree rings show that this was also the case during the Roman times when temperatures were almost 1 degrees warmer than today
• Little Ice Age


  • A period of cooling that followed the Medieval Warm Period
  • Paintings from the 17th Century show the London Frost Fairs, which took place on a frozen river Thames
  • Historical records talk about arctic ice reaching as far south as Scotland
• There is a scientific consensus (general agreement) that human activities are causing global warming by making the greenhouse effect stronger
• Greenhouse effect


  Too much greenhouse gas in the atmosphere means too much energy is trapped and the planet warms up
• How humans are increasing greenhouse gases

  • Farming
  • Industry
  • Energy
  • Transport
• Farming


  • Produces a lot of methane
  • Rice paddies- flooded fields emit methane
  • Deforestation for agriculture stops carbon dioxide being absorbed
• Industry


  • Use a lot of energy
  • Industrial processes release greenhouse gases e.g. cement releases a lot of carbon dioxide
  • Industrial waste enters landfills and decays producing methane
• Energy


  CO2 is released into the atmosphere when fossil fuels are burnt (coal, oil and natural gas)
• Transport


  • Most cars, lorries, ships and planes run on fossil fuels
  • Car ownership is rapidly increasing in developing countries (China and India)
  • This means there are more cars on the road especially in urban areas
  • This increases congestion. As a result car engines are running for longer, so the amount of greenhouse gases being released increases
• Plate Boundaries


  • Divergent
  • Convergent
  • Conservative
  • Collision
• Hotspots


  • Occur when a plume of hot magma from the mantle moves towards the surface
  • Sometimes the magma can break through the crust and reach the surface
  • When this happens there is an eruption and a volcano forms
  • Hotspots remain stationary over time, but the crust moves above them. This can create chains of volcanic islands
  • An example is Hawaii
• Volcano Types


  • Shield Volcano
  • Composite Volcano
• Shield Volcano


  • Low, gently sloping domes with a very wide base
  • Only layers of lava
  • Basaltic lava
  • Low silica content, runny, flows long distances
  • Frequent eruptions
  • Gentle eruptions
  • Lava flows
• Composite Volcano


  • Tall, steep-sided cone with a narrow base
  • Layers of ash and lava
  • Andesitic lava
  • Viscous (thick and sticky)
  • Infrequent eruptions
  • Violent eruptions due to rock plug created by solidified lava from a previous eruption
  • Lava bombs
  • Pyroclastic flows
  • Lahars
  • The lava can't flow far so forms a steep-sided cone
• Factors affecting earthquake size

  • Plate boundary
  • Depth of focus
  • Tsunamis: Water gets displaced, Depth affects tsunami size, Waves travel very fast in deep water
• Conditions for tropical storm formation

  • Large, still, warm ocean at 26.5°C
  • Strong winds high in the troposphere, 10-12km above the Earth's surface, are needed to draw warm air up rapidly from the ocean surface
  • Form where the rotation is stronger between 5° and 30° latitude north and south of the equator – at the Tropics
  • They can only form in late summer when oceans have warmed up – mid-July to October in the northern hemisphere, and mid-January to April in the southern
• Tropical storm characteristics


  • Earth's rotation deflects the paths of the winds causing it to spin
  • Cyclones intensify due to warm water
  • Dissipate when they move over land or cold water
  • Move towards the west because of the easterly winds near the equator
  • When they travel further away from the equator they start to curve east as they get caught in the mid-latitude westerlies