• 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• the centripetal force of the rotating earth

Diurnal Tide: 24 hr 50 min cycleSemi Diurnal Tide: 12 hr 25 min cycleMixed Tide: 12 hr 25 min cycle

Tides are generated by:

Sun

Earth

Earth

EarthMoon

Moon

Moon

Tides

A. Gravitational pull

B. Centripetal force

C. Gravitational pull & Centripetal force

center of mass

Bulge of water

• 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: 1st quarter and 3rd quarter (14.77 days)

Description of tides

Intertidal zoneHigh tide

Low tide

Spring TideHighest high tide and lowest low tide

full moon

new moon

earth

earth

3rd quarter moon

Neap Tide

earth

1st quarter moon

Tidal PatternsSemidiurnal tides- two high and two low per day; Cape Cod, MA (low latitudes)Diurnal tides- one high and one low per day; Mobile, AL (high 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

6 ft

Tidal Range

56 ft

Alma at High Tide

Alma at Low Tide

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

http://life.bio.sunysb.edu/marinebio/mbweb.html

Tidal Information

HAWAIIAN ISLANDSMean Spring Mean Tide        Station Latitude Longitude Range Range Level Predictions SAND ISLAND, MIDWAY ISLANDS 28° 12.7' 177° 21.6' 0.8 1.2 0.6 Predictions

Laysan Island 25° 46' 171° 45' 0.7 1.0 0.4 Predictions East Island, French Frigate Shoals 23° 47' 166° 13' 0.9 1.4 0.6 Predictions Nonopapa, Niihau Island 21° 52' 160° 14' 1.0 1.6 0.7 Predictions

Kauai Island Waimea Bay 21° 57' 159° 40' 1.0 1.6 0.7 Predictions Port Allen, Hanapepe Bay 21° 54' 159° 35' 1.1 1.7 0.7 Predictions NAWILIWILI 21° 57.4' 159° 21.6' Predictions Hanamaulu Bay 22° 00' 159° 20' 0.0 1.2 1.8 Predictions Hanalei Bay 22° 13' 159° 30' 1.3 1.8 0.8 Predictions

Oahu Island Haleiwa, Waialua Bay 21° 36' 158° 07' - - 1.6 0.7 Predictions Waianae 21° 27' 158° 12' 1.2 1.8 0.8 Predictions

HONOLULU 21° 18' 157° 52' 1.3 2.0 0.8 Predictions Hanauma Bay 21° 17' 157° 42' 1.3 1.9 0.8 Predictions Waimanalo 21° 20' 157° 42' 1.1 1.8 0.8 Predictions MOKUOLOE 21° 26.2' 157° 47.6' 1.2 2.0 1.0 Predictions Waikane, Kaneohe Bay 21° 30' 157° 51' 1.4 2.2 1.1 Predictions