Animation of Tidal Elevations in the Pacific. Tides and Tsunamis Gravitational forces of moon and...
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Transcript of Animation of Tidal Elevations in the Pacific. Tides and Tsunamis Gravitational forces of moon and...
Animation of Tidal Elevations in the Pacific
Tides and Tsunamis
• Gravitational forces of moon and sun• Equilibrium theory of Tides• Dynamic theory of Tides (Reality): tidal
patterns, confined basins
• Tsunamis: generating forces• Effects of tsunamis• Warning systems, defenses
Equilibrium Theory
Tides are always in equilibrium withthe gravitational pull of the moon andEarth is a planet covered in water.
Assumption
Gravity and centrifugal force(also called “tractive forces”)
Together:The earth-moon system
Equilibrium theory of tides
Tides: The moon and the sun together
Spring tide
Neap tide
semidiurnal
diurnal
composite
+
=
Dynamic Theory
Waves travel at a fixed waves speedThere are continents and rotation
Needs to account for:
Tidal circulation
• Tides progress around basins, counterclockwise in S hemisphere and clockwise in N hemisphere
Animation of Tidal Elevations in the Pacific
Inertia + continents cause the tidal motion on the planet to differ markedly from the “motion” of the forces.
We can calculate the water motion knowing the forces, but we cannot say that the shape of the water is the same as the “shape” of the forces.
For this reason tides must not be visualized as bulges standing under the sun and moon.
But rather as very long waves over the sea forced by the gravitational-centrifugal forces associated with the moon-sun-earth system.
Tides in confined basins• Increase tidal range (the difference
between high and low tide)
• Examples--Bay of Fundy, Canada--Northern Gulf of California, Mexico
• Tidal bores - wave of water moving upstream - result of high-tide crest entering confined inlet
Bay of Fundy: map
• 2.416
Bay of Fundy tides
• Extreme tides (10m or more) found where small marine basin adjoins large ocean– Bay of Fundy, Nova Scotia– Gulf of California
• (in most places, tides are 1 to a few meters in range)
Shock Waves and Tidal Bores are similar!
Tidal bore: Severn River, England
• 2.452
Tidal ecosystems
• Rise and fall of tides creates stressful environments for intertidal marine organisms
Tidal ecosystems
• Others take refuge in tide pools, where water remains even at low tide
TsunamiJapanese for harbor (tsu) wave (nami)
Caused by displacements of water•landslides into the sea•submarine earthquakes•submarine volcanoes•asteroid impacts
“Shallow-water” wave: disturbs water all the way to bottom
Tsunami of April 1, 1946
Earthquake triggers tsunami with devastating local and distant effects
The speed of the tsunami wave
C = sqrt(g d)
C = speed,
g = acceleration due to gravity (9.8 m/sec/sec)
d = depth (depth of Pacific ~4,600 m)
C= sqrt(9.8 * 4,600)
Speed = 212 meters per second; 472 mph
Alaska to Hawaii in 5 hours!
Locally, the tsunami washed away the 5-story lighthouse at Scotch Cap, Alaska
Before… and after
Hilo, Hawaii, 1946: Tsunami crossed the north Pacific to become one of Hawaii’s worst natural disasters
Hilo, Hawaii, 1946
Tsunami breaking over main pier in Hilo, 1946
This man did not survive
Chile earthquake, 1960numerical simulation of tsunami
8.5 hours
1.5 hours 16.5 hours
23.5 hours
Aftermath of local tsunami: Chiloe, Chile, 1960
Distant effects of the Chile earthquake: tidal wave aftermath, Hilo Hawaii
More tsunami damage in Hilo, 1960
Tsunamis: what can be done?• Early warning system for evacuation (if EQ is distant)• Coastal zoning. Get development out of the way. Example: Hilo,
Hawaii• Defense. Protective walls. Example: Taro, Japan