2 Tides and Tsunamis Gravitational forces of moon and sun Equilibrium theory of TidesDynamic theory of Tides (Reality): tidal patterns, confined basinsTsunamis: generating forcesEffects of tsunamisWarning systems, defenses
3 Equilibrium Theory Assumption Tides are always in equilibrium with the gravitational pull of the moon andEarth is a planet covered in water.
15 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.
16 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
22 Tidal ecosystemsRise and fall of tides creates stressful environments for intertidal marine organisms
23 Tidal ecosystemsOthers take refuge in tide pools, where water remains even at low tide
24 Tsunami Japanese for harbor (tsu) wave (nami) Caused by displacements of waterlandslides into the seasubmarine earthquakessubmarine volcanoesasteroid impacts“Shallow-water” wave: disturbs water all the way to bottom
25 Tsunami of April 1, 1946Earthquake triggers tsunami with devastating local and distant effects
26 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 mphAlaska to Hawaii in 5 hours!
27 Before… and afterLocally, the tsunami washed away the 5-story lighthouse at Scotch Cap, Alaska
28 Hilo, Hawaii, 1946: Tsunami crossed the north Pacific to become one of Hawaii’s worst natural disasters
35 Tsunamis: what can be done? Early warning system for evacuation (if EQ is distant)Coastal zoning. Get development out of the way. Example: Hilo, HawaiiDefense. Protective walls. Example: Taro, Japan