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Oceanography 112
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ANSWERS TO STUDY QUESTIONS CHAPTER 11

1. Tsunamis are usually caused by permanent vertical sea floor displacement. Such displacement is commonly accompanied by earthquakes, but earthquakes rarely cause tsunamis. Since tsunamis have wave lengths which exceed the ocean’s depth by more than 20 times, they behave like shallow water waves and so their velocity is controlled only by water depth.

2. mixed; mean lower low water, that is the average of all the lower of the two low tides

2. The moon does not supply enough gravity there to completely compensate for the water’s inertia.

3. The tide generating force due to the moon is about twice that of the sun.

4. The period of the lunar tide would be 12 hours and 25 minutes making the assumptions of equilibrium theory.

5. The sun's declination varies on a yearly cycle. It changes from 23.5o south in December, to 23.5o north in June. Twice each year it becomes zero on the spring and fall equinoxes.

6. Precession changes the moon's maximum declination per synodic month from 28.5o to 18.5o.

7. Due to declination, the tidal bulges are rarely aligned with the equator - one will be in the northern hemisphere and the other in the southern hemisphere. An observer rotating with the earth stays in the same hemisphere and thus will pass through the tidal bulges at different distances from their centers. The higher of the two high tides occurs when the observer passes through the bulge that is centered in his/her hemisphere.

8. Tidal ranges will be maximum at perigee and perihelion.

9. The continents confine the tide waves to basins, which causes the tides become seiche-like. Coriolis effect turns the tide waves as they slosh back and forth so the net effect is for the tide waves to rotate.

10. Ebb currents are fastest about 3 hours after high tide and flood currents fastest about 3 hours after low tide.

11. Tidal bores are most likely to occur in situations where the:

(1) seiche period in a bay/river mouth approximates the tidal period,

(2) bay/river mouth is funnel-shaped,

(3) bay/river mouth is far from an amphidromic point, and the

(4) river gets shallower upstream.
Last Updated: 01/13/2015
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