SA challenge of natural hazards

• Natural hazard


  A natural event that can cause social and economic impacts
• Social impacts


  • Impacts on people and their lives, mainly injuries and deaths
• Economic impacts


  • Effects on jobs and money, often refers to the cost of the damage or jobs lost
• Natural hazards must be created by nature, not man-made hazards like radiation leaks or oil spills
• A natural hazard must have social and economic impacts, otherwise it is just a natural event
• Examples of natural hazards

  • Earthquakes
  • Volcanoes
  • Tropical storms
  • Droughts
  • Heat waves
  • Tornadoes
  • Flooding
  • Wildfires
• Weather/climatic/atmospheric hazards


  Hazards created by the weather
• Geological/tectonic hazards


  Hazards created by processes taking place inside the planet
• Plate boundaries


  Also called plate margins, the parts of the world where one tectonic plate is next to another
• Constructive (divergent) plate boundaries


  • Magma rising up in the mantle below, cooling off and spreading out to create new crust
  • Mostly appear at the bottom of the sea, with some evidence on land like in Iceland
• Destructive (convergent) plate boundaries

  • Oceanic plate being forced underneath continental plate in subduction
  • Water and dead plankton dragged down, turned into water vapour and carbon dioxide which melt continental crust above
  • Pressure builds up and erupts violently
• Collision (convergent) plate boundaries

  • Both plates are continental, so they crash head-on and crumple upwards to form mountains
  • Plates grind, crack and buckle upwards over millions of years, getting stuck and then unsticking to cause earthquakes
• No volcanoes at collision boundaries as there is no magma rising up from underneath
• Conservative (transform) plate boundaries

  • Tectonic plates sliding past each other, either in opposite directions or at different speeds
  • Edges of plates get stuck and then jump back into moving, releasing energy and causing earthquakes
• No volcanoes at conservative (transform) boundaries as there is no magma rising up from underneath
• Gulf Stream


  A warm stream of surface water that circulates around the Atlantic Ocean, the North Atlantic drift is an offshoot that circulates warm water around the Silly Isles, keeping sea surface temperature above 11°C in winter
• The Gulf Stream is partly caused by the circulation of ocean waters but is mainly driven by winds
• The Earth's climate, ocean currents, and global atmospheric circulation or large-scale winds are interconnected
• While storms are raging in the North Atlantic in February, in the southern hemisphere Central Australia can be suffering intense heat and heavy tropical rains might be falling in the Amazon rainforests
• Global circulation model


  Explains the Earth's atmospheric circulation, heating and cooling effects around the globe are driven by wind
• Heat from the Sun

  Energy from the Sun is shortwave light radiation, not actual heat; the heat we feel comes from light absorbed on the Earth's surface, which is converted into longwave radiation
• Our location on Earth plays a major part in determining the amount of heat we feel
• In the Sahara during the hottest months, air temperatures can rise above 50°C
• Over the course of one year, the intensity of solar radiation or insolation is greatest over the equator because the Sun is directly overhead
• At the polar caps, the Sun hits the Earth's surface at a much lower angle, so the same amount of energy is spread over a much larger area, which means it's cooler
• Polar ice sheets also reflect most of the sunlight that does reach the surface
• There is an excess of heat at the equator and a deficit at the poles
• Tropical storms


  Low pressure weather systems with intense rainfall and winds
• Low pressure just means when warm air rises
• A hurricane, typhoon and cyclone are all the exact same thing, they are just named differently dependent on the location they were formed
• Conditions needed for a tropical storm to form

  • It must be between 5 and 30 degrees north and south of the equator
  • The sea temperatures must be at a minimum of 27 degrees celsius
  • The wind shear which is the difference in wind speed must be low
• How tropical storms develop

  1. Warm surface water evaporates, rises and condenses into clouds, releasing energy to fuel the storm

  2. Rising air creates low pressure, increasing surface winds due to the Coriolis force

  3. As the storm moves over the ocean, the energy from the warm water supply strengthens the storm
• Features and structures of a tropical storm

  • The center of the storm is called the eye, with very low pressure, light winds, no clouds and high temperature
  • The eye is surrounded by the eye wall, with spiraling rising air, very strong winds, storm clouds and torrential rain
  • Towards the outer skirts of the storm, the wind speeds fall, the clouds become smaller and more scattered, and the rain becomes less intensive as the temperature increases
• How climate change may affect tropical storms

  • Oceans will stay at 27 degrees celsius or higher for longer each year, allowing more time for storms to form
  • More of the world's oceans could be above 27 degrees celsius, meaning tropical storms may form in new areas
  • Higher sea surface temperatures are likely to result in more evaporation, increased cloud formation and more energy released, making storms more powerful
• How to reduce the effect of tropical storms

  1. Prediction and monitoring using radar and satellites

  2. Planning future developments to avoid low-lying coastal areas and preparing evacuation plans and emergency services

  3. Protection through buildings designed to withstand storms and flood defences
• Prolonged rainfall and flooding

  Persistent rainfall over a long period of time can lead to river floods as the ground becomes saturated and there is more surface runoff into rivers
• Prolonged rainfall and flooding


  • Flooding across much of Southern England including Somerset Levels during the very wet winter of 2013 to 2014
• River flash flooding


  Intense rainfall brings a huge amount of water into an area in a short space of time, common in upland areas with steep slopes
• River flash flooding


  • When Storm Desmond hit the Lake District in December 2015
  • When over 18cm of rainfall fell in 5 hours in Boscastle, Cornwall in August 2004
• Coastal flooding


  A deep depression causes strong winds that bring a storm surge into a major river estuary, funnelling coastal water into the mouth of a river