2. Tides are generated by: the gravitational pull of the moon and sun - moon has 2x greater gravitational pull than the sun - sun is 10 million x more massive than the moon and is 390 times farther away

4. High water: a water level maximum ("high tide") Low water: a water level minimum ("low tide") Tidal range: the difference between high and low tide Spring Tide: full moon and new moon (14.77 days) Neap Tide: 1 st quarter and 3 rd quarter (14.77 days) Description of tides Intertidal zone High tide Low tide

7. Earth-Moon-Sun positions and the monthly tidal cycle Spring Tide Highest high tide and lowest low tide Neap Tide Moderate tidal range

8. 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

9. Diurnal Tide: 24 hr 50 min cycle Semi Diurnal Tide: 12 hr 25 min cycle Tidal Cycles

10. Tidal Patterns Semidiurnal tides- two high and two low per day; Cape Cod, MA (high latitudes) Diurnal tides- one high and one low per day; Mobile, AL (low latitudes) Mixed pattern tides- Two high and two low tides per day BUT with successive high tide levels that are VERY DIFFERENT from each other; Hawaii (mid latitudes) Type of tide depends on: Position on the globe Water depth Contour- shape of ocean basins

14. 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)

15. Alma at High Tide Alma at Low Tide

16. La Rance tidal power plant at St. Malo, France.

17. Corals exposed to air at extreme low tide

18. Inquiry 1.Which has the greatest tidal effect– sun or moon? 2.Where is the greatest tidal range located? 3.Which lunar phase produces moderate tides? 4.How is a tidal bore created? www.wcc.hawaii.edu/.../OCN%20201%20PPT/010-Tides.ppt