hurricane ike. natural hazards and disasters chapter 5 tsunami
TRANSCRIPT
Tsunami have many causes• Sudden displacement of large volume of water
– Earthquake– Volcanic eruptions– landslides or rockfalls– volcano flank collapses– asteroid impacts
GLG110 Fall 2002 Arrowsmith
Tsunami have two waves
Panel 1--Initiation: Near the source of submarine earthquakes, the seafloor is "permanently" uplifted and down-dropped, pushing the entire water column up and down. Pushing water above mean sea level then drives horizontal propagation of the tsunami wave.Panel 2--Split: Initial tsunami split into a tsunami that travels out to the deep ocean (distant tsunami) and another tsunami that travels towards the nearby coast (local tsunami).
GLG110 Fall 2002 Arrowsmith
Life of a Tsunami—cont’dhttp://walrus.wr.usgs.gov/tsunami/basics.html
Panel 3--Amplification: As the local tsunami travels over the continental slope, the amplitude increases and the wavelength decreases. This results in steepening of the leading wave--an important control of wave runup at the coast (next panel).
Panel 4--Runup: Most tsunamis do not result in giant breaking waves. Rather, they come in much like very strong and very fast tides (i.e., a rapid, local rise in sea level). Much of the damage inflicted by tsunamis is caused by strong currents and floating debris. After runup, part of the tsunami energy is reflected back to the open ocean.
Tsunami Movement
• Waves described by wavelength, height, period
• Tsunami in open ocean:– Small wave heights– Average wavelength about 360 kilometers– Period may be half an hour
Tsunami Movement• Typical waves:
– Driven by wind– Particles travel in circular
motion that fades downward– Velocity depends on
wavelength– ‘Touch bottom’ at depths less
than half wavelength• Tsunami waves:
– Enormously long wavelength– ‘Touch bottom’ everywhere in
ocean– Velocity depends on water
depth– Slow down dramatically in
shallower water
Tsunami Movement• Tsunami waves in open
ocean:– Travel as fast as 870
kilometers per hour– May slow to 150-300 km/hr
on continental shelf• Tsunami waves in
shallower water:– Front of wave slows first but
rear keeps coming– Wave becomes much shorter– Volume of wave remains
same– Height must rise dramatically,
up to six times height in open ocean