Tectonic Hazards - Hazards (Primary & Secondary) In Tectonics Processes

Earthquake Hazards:
  • Crustal fracturing (ground displacement) - – cracks open up in the earth and land can rise and fall
  • Ground shaking – the ground moves rapidly side to side, and up and down, due to seismic waves
Secondary Hazards:
  • Landslides - soil and rocks are shaken loose, and rapidly fall downhill under gravity
  • Tsunamis - the earth’s crust under the ocean displaces water in an earthquake and creates huge waves
  • Liquefaction (when soil on the surface turns into liquid making quicksand because it is on soft earth) - the ground shaking causes groundwater to come to the surface
Types Of Waves In Earthquakes:
  • Primary waves – fastest but least damaging
  • Secondary waves – vibrations at right angles
  • Love waves – horizontal surface movement
  • Rayleigh waves – ‘rolling’ surface waves
Tsunamis:
How Does A Tsunami Occur/Form?
  1. An sub-marine earthquake occurs under the ocean at subduction zones, such as Japan trench 2011
  2. The fault slip thrusts rock up into the water
  3. A large amount of water is ‘displaced’ (this means moved to somewhere else!)
  4. The upwards ‘water column displacement’ of water is like throwing a pebble in a pond: the water ripples outwards
  5. As the waves approach the shallow coastal waters, the wave ‘backs up’ (front slows due to beach and back catches up)
  6. This means the waves become very tall and form a tsunami, flooding the land e.g. Japan 2011
Volcanic Hazards (Primary):
  • Lava flow - Lava flows are hot molten rock that has escaped from fissures in the earth’s crust. Burn buildings etc.
  • Pyroclastic flow - very hot ash clouds that are large particles too heavy to rise, so they fall quickly and sink/flow down the volcano side. Spread very fast and kill locals.
  • Ash fall & volcanic bombs (tephra) - fine particles of rock that have come from ‘vaporised’ magma – the pressure of the magma blows it to tiny pieces of ash that rise in the air. Damages lungs and aeroplanes.
  • Gas eruptions - the release of carbon dioxide & sulphur dioxide from volcanoes. Can suffocate people.
Secondary Hazards:
  • Lahars (mudflows) - volcanic mudflows when ash mixes with water (from rain or snow/glacier meltwater). They flow like concrete and flood and bury people and houses. E.g. Pinatubo
  • Jokulhlaups (glacial flooding) - huge floods that are caused by large ice-caps melting when a volcano erupts under the ice e.g. Iceland 2010
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