Plate Tectonics and Associated Hazards Tsunamis

Tsunamis: Giant sea waves generated by shallow-focus underwater earthquakes, volcanic eruptions, underwater debris slides and large landslides into the sea.

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  • Created on: 11-09-12 00:28
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Plate Tectonics and Associated Hazards
Tsunamis: Giant sea waves generated by shallowfocus underwater earthquakes, volcanic
eruptions, underwater debris slides and large landslides into the sea.
Open ocean:
Very long wave length (100km)
Low wave height (under 1m)
Travel quickly (Greater speeds than 70 km h1)
On reaching shallow water bordering land they rapidly increase in height as the wave
slows at the front, but continues at the same speed behind, forcing it upwards
increasing the wave height.
Causes a drawdown, where the wave trough in front of the tsunami causes a reduction in
sea level.
Behind the Tsunami can reach heights in access of 25m and consists of a number of waves
which the first not necessarily being the largest.
When a Tsunami reaches land, its effect depend on a number of factors
height of the wave and the distance they have travelled (the fetch)
length of the event that caused the tsunami
extent to which warnings can be given
coastal physical geography, offshore and onshore
Coastal land use and population density
Effects
Wave will wash boats and wooden structures inland and the backwash carry them
out to sea
The water itself and debris cause drowning and injuries
The effects of most are felt 500600m inland depending on coastal geography
Buildings, roads, bridges, harbour structures, trees and soil are washed away.
90% of tsunamis are generated within the Pacific basin and are associated with the
tectonic activity taking place around its edges

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