The Restless Seas Tides and Waves
Tides • The daily rise and fall of the ocean seen along the shore • Extremely long wavesmoving through the oceans • High tide: when the ocean reaches its highest elevation on the shore • Low tide: when the ocean reaches its lowest elevation along the shore
Tide Range • The vertical distance between high and low tides • Ebb tide: falling or out going tide • Flood tide: incoming or rising tide
Gravity and Tides • The interaction between the Earth and the mooncauses two tidal bulges on opposite sides of the planet. • The bulge on the side of the Earth closest to the moon is a consequence of the mutual attraction between the moon and the Earth (gravitational attraction). • The bulge on the opposite side results from the centrifugal force created as Earth and moon revolve around a common point (barycenter).
Gravity and Tides • Each tidal location is approximately six and a quarter hours apart • The sun also exerts a gravitational pull on Earth. • Less than moon because of distance
Spring Tides • Greatest tidal range (highest and lowest tide) • Occur twice each month during new and full moon • The sun, moon and Earth align • The gravitational effects of both sun and moon combine. • Name comes from German word “Springen” or to jump up.
Neap Tides • When the moon is in the first-quarter and third quarter phases • Pull of moon and sun are at right angles • Produces weaker tides • Name comes from German word “nepfold” or napping
Nova Scotia’s Bay of Fundy http://home.hiwaay.net/~krcool/Astro/moon/moontides/
Three General Types of Tides • Different tidal ranges in different part of the world because of depth and shape of the ocean basin and coastline • Semidiurnal: two equal high and low tides each day (East Coast of U.S.) • Diurnal: (rare) only one high and one low (Parts of G. of Mexico, Vietnam, Manila) • Semidiurnal Mixed: tides occur twice a day but are unequal in height. (West Coast of U.S.)
Grunion (Leuresthes tenuis): • Grunion (Leuresthes tenuis): fish swim up on the beach during high tide. (New and Full moon) Reproduce and bury eggs in the sand. Eggs incubate in 2 weeks, hatch at high tide.
Horseshoe Crab (Limulus polyphemus): • Horseshoe Crab (Limulus polyphemus): Late May- early June come nearer to shore to spawn, come to shore during high tide.
Anatomy of a Wave cont. • Wave: is the up and down movement of the ocean surface. Form of energy. Most are caused by winds. • Wave Train: series of waves moving in the same direction • Speed of a wave (V) = wavelength (W)/ Period (P) • W= 10 m and p= 5 secs
Velocity Calculation • Speed of a wave (V) = 10m/ 5s • V= 2 m/s
Wave Vocabulary • Ripples: small wavelets averaging about 8 cm high. • Chop: wind pushes ripples into waves 1 meter high. (winds increase velocity). • Storm Waves: gale force winds (> 70 km/hr)
Wave Vocab Cont. • Swells: created when waves move beyond windy area in which they are generated and have longer periods and more rounded crests. Form in deep water. • Breaker: formed when the water depth is less than one-half the wavelength of the top of the wave. The water moves faster on top causing it to pitch forward and crash.
Destructive Waves • Tsunami: (Japanese for harbor wave) created by seismic activity such as earthquakes, landslide, orvolcanic eruption. • Storm Surge: extra high water created by ahurricane (also called typhoon or tropical cyclones in other parts of the world) • Tidal Bore : incoming tide enters a harbor or river where the water level is higher. Can cause flooding.