The Restless Seas

Tides and Waves

Tides

• The daily rise and fall of the ocean seen along the shore

• Extremely long waves moving 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 moon

causes 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

1. Semidiurnal: two equal high and low tides each day (East Coast of U.S.)

2. Diurnal: (rare) only one high and one low (Parts of G. of Mexico, Vietnam, Manila)

3. 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

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)

Ripples

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.

Breaker

Destructive Waves

• Tsunami: (Japanese for harbor wave) created by seismic activity such as earthquakes, landslide, or volcanic eruption.

• Storm Surge: extra high water created by a hurricane (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.