1. Tides!!!!!!!!!!!

2. Tides Periodic, short-term changes in ocean height Periodic, short-term changes in ocean height

3. What causes tides? Gravitational force of the sun and moon Gravitational force of the sun and moon

4. Sun is 27 million times more massive than the moon… Sun is 27 million times more massive than the moon…

5. But the sun is 387 times farther away But the sun is 387 times farther away

6. Distance plays a larger role than the masses of the bodies involved Distance plays a larger role than the masses of the bodies involved

11. Tidal Range The difference in ocean level between high and low tide

12. The monthly tidal cycle (29½ days) About every 7 days, Earth alternates between: Spring tide Alignment of Earth-Moon-Sun system (syzygy) Lunar and solar bulges constructively interfere Large tidal range Neap tide Earth-Moon-Sun system at right angles (quadrature) Lunar and solar bulges destructively interfere Small tidal range

13. Spring Tides Earth, Moon, and Sun are lined up High Tides are higher and Low Tides are lower than normal

14. Neap Tides Earth, Moon, and Sun form right angles High Tides are lower and Low Tides are higher than normal

15. Variations in tidal form world wide

16. Tidal patterns Diurnal One high and one low tide each (lunar) day Semidiurnal Two high and two low tides of about the same height daily Mixed Characteristics of both diurnal and semidiurnal with successive high and/or low tides having significantly different heights

17. Variable Tides

18. Monthly tidal curves Figure 9-16

19. semidiurnal Mixed, SD dominant Mixed, D dominant diurnal

20. The Bay of Fundy: Site of the world’s largest tidal range Tidal energy is focused by shape and shallowness of bay Maximum spring tidal range in Minas Basin = 17 meters (56 feet) Figure 9-17

21. Bay of Fundy High tide Low tide (  6 hours later) Video Clip: http://www.youtube.com/watch?v=qfhNjpu_IU4

22. St. Michel, N. coast of France ~16.8 m highest tidal range in Nova Scotia

23. Coastal tidal currents Tidal currents occur in some bays and rivers due to a change in tides Ebb currents produced by outgoing tides Flood currents produced by incoming tides Figure 9-18

24. Tidal bore = a true tidal wave Wall of water that moves upriver Caused by an incoming high tide Occurs in some low-lying rivers Can be large enough to surf or raft Figure 9B Video Clips: http://www.youtube.com/watch?v=LWumonz87rA http://www.youtube.com/watch?v=IKA39LQOIck

25. Grunion and the tides Grunion are the only fish that come completely out of water to spawn Spawning cycles are timed precisely with the tides Figure 9C Video Clip: http://www.youtube.com/watch?v=udRDj2Ez8kI

26. Sites with high potential for tidal power generation Figure 9-19