Tsunami is a harbor wave Waves rise highest where focused in
bays or harbors
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Tsunami have many causes Sudden displacement of large volume of
water Earthquake Volcanic eruptions landslides or rockfalls volcano
flank collapses asteroid impacts
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San Francisco
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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).
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GLG110 Fall 2002 Arrowsmith Life of a Tsunamicontd
http://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.
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Tsunami speed and height Initial wave is 1 meter tall but moves
500 mph Wave at shoreline is 10 m tall but moves 30 mph Waves
heights range 8-40 feet (but can be 100 ft) Wave speed = square
root of g * height
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Tsunami speed and height
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Earthquake-Generated Tsunami
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Tsunami from Volcano Flank Collapse
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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
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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
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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
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Tsunami travels rapidly.
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Tsunami Warnings
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Case In Point: Lituya Bay
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Case In Point
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Thailand Earthquake 2 hours later, giant wave surged More than
5000 people died in that area
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In minutes 230,000 people lost their lives, and over 430,000
homes were reduced to rubble
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Over 100,000 fishing boats were destroyed. The livelihoods of
over 5 million people were thrown into jeopardy
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More than 2,174 miles of roads destroyed. $10 billion in
damages in barely 24 hours.
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Tsunami Experiments
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What to do in a Tsunami Be aware after large local earthquake
Obey Tsunami warnings The first wave is not the biggest Elevation
is key: hills, upper floors, trees Move inland, even if it is
flat
