TECTONICS - Causes of tsunamis and volcanoes

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  • Causes of volcanoes and tsunami's
    • volcanoes
      • Secondary hazards include lava flows, pyroclastic flows, ash falls, gas eruptions, lahars and jokulhlaups.
      • occur at destructive plate margins.
      • composite cone volcanoes threaten the most danger, whereby areas up to 30km away may be affected.
    • Tsunamis
      • Can be generated by landslides and even eruptions on volcanic islands. most are generated by sub-marine earthquakes at subduction zones.
        • A vertical displacement of the sea bed (up or down) called slab-pull, at a subduction zone. This displaces a large volume of water.
      • Characteristics of tsunami waves in deep ocean:
        • wave heights less than 1m.
        • wave lengths of more than 100km.
        • speeds of 500-950 km/h.
        • As they approach the shore:
          • slow dramatically, wavelength drop and wave height increases.
          • May hit the shore in a series (wave-train).
      • the 2004 Indian Ocean Tsunami
        • killed 230,000–280,000 people.
        • The undersea megathrust earthquake was caused when the Indian Plate subducted beneath the Burma Plate.
        • a moment magnitude (MMI) of 9.1–9.3 and a maximum  Mercalli intensity of IX (Violent).

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