1. Animation of Tidal Elevations in the Pacific

2. 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

3. Equilibrium Theory Assumption Tides are always in equilibrium with
the gravitational pull of the moon and
Earth is a planet covered in water.

5. Gravity and centrifugal force (also called “tractive forces”)
Equilibrium theory of tides
Together:The earth-moon system

6. Tides: The moon and the sun together
Spring tide
Neap tide

9. semidiurnal +
diurnal =
composite

10. Dynamic Theory Needs to account for:
Waves travel at a fixed waves speed
There are continents and rotation

12. See video

13. Tidal circulation
Tides progress around basins, counterclockwise in S hemisphere and clockwise in N hemisphere

14. Animation of Tidal Elevations in the Pacific

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

18. Bay of Fundy: map
2.416

19. 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)

20. Shock Waves and Tidal Bores are similar!

21. Tidal bore: Severn River, England
2.452

22. Tidal ecosystems
Rise and fall of tides creates stressful environments for intertidal marine organisms

23. Tidal ecosystems
Others take refuge in tide pools, where water remains even at low tide

24. Tsunami Japanese 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

25. Tsunami of April 1, 1946
Earthquake 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 mph
Alaska to Hawaii in 5 hours!

27. Before… and after
Locally, 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

29. Hilo, Hawaii, 1946

30. Tsunami breaking over main pier in Hilo, 1946
This man did not survive

31. Chile earthquake, 1960 numerical simulation of tsunami
1.5 hours
16.5 hours
8.5 hours
23.5 hours

32. Aftermath of local tsunami: Chiloe, Chile, 1960

33. Distant effects of the Chile earthquake: tidal wave aftermath, Hilo Hawaii

34. More tsunami damage in Hilo, 1960

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, Hawaii
Defense. Protective walls. Example: Taro, Japan