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Published byAndy Eckford Modified over 2 years ago

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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

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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

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

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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

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

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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

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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)

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Alma at High Tide Alma at Low Tide

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

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Corals exposed to air at extreme low tide

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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

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