1.Gravitational pull of the moon and sun

2.Centripetal force of the rotating Earth

Tides are generated by:

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

Centripetal force

CENTRIPETAL

GRAVITATIONAL FORCE

GRAVITATIONAL & CENTRIPETAL

• Diurnal Tide: 24 hr 50 min cycle

• Semi Diurnal Tide: 12 hr 25 min cycle

• Mixed Tide: 12 hr 25 min cycle

Tidal Cycles

• 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

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

Earth-Moon-Sun positions and the monthly tidal cycle

Spring TideHighest high tide and lowest low tide

Neap TideModerate tidal range

Tidal PatternsSemidiurnal 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

6 ft

Tidal Range

56 ft

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)

Alma at High Tide

Alma at Low Tide

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

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

Corals exposed to air at extreme low tide

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

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?