= Giant sea wave caused by displacement of large volumes of water. Most are secondary hazards of earthquakes.
- More powerful if it starts close to coast, because it loses energy as they travel in land.
- Travel fast in deep water, hits shore without much warning.
- Affects the whole coloumn of water- surface to seabed
OPEN OCEAN- water is deep, long wavelength of 200km, with a small wave height (amplitude) of 1m and high wave speeds of 500-950km/h
CLOSE TO LAND- water is shallow, decreasing wavelength to less than 20km, amplitude increases to many metres, wave speed begins to slow to 80km/h ---> shallower water- waves are compresed, energy is concentrated.
Stages of a tsunami
Generation of tsunami in deep ocean as a result of the displacement of large area of sea floor- displacing large amounts of sea water.
2) Tsunami run-up
-Water shallows, wave slows and increases in height. Sea-floor irregularities reflect some wave energy- seafloor topography in costal zone important in nature of tsunami.
-Nature of wave depends on the causes of the wave, the distance travelled from source as energy is lost as it travels inland, water depth over route affects energy through loss of friction and offshore topography
Depth and destruction depend on land uses, population density and warning given.
- Event consist of sequence of waves, can last for several hours, 4th/5th waves often the largest
- 40% of wave energy is scattered back to the sea, 60% expanded at coastline
- As waves reaches the shore, water will drawback- wave troughs at front
- Most generated at subduction convergent plate boundary and pacific coast (90%)