Ocean Waves & Tides

Waves

The result of repeated and periodic disturbances that cause energy to be transported through water.

Very little water is transported.• Wind• Turbidity currents• Earthquakes

Wind Generated waves

Size of the wave is determined by:1. The duration of the wind-how long it blows.

2. The strength of the wind- how fast it blows.

3. The fetch- the distance over the ocean’s surface the wind blows.

• Longer the wind blows- bigger waves• Stronger the wind blows- higher the

waves• Greater the fetch- bigger waves

Types of Waves

Waves are classified according to their wave-length:

Wave period: Time in seconds between the passage of successive wave crests or troughs at a stationary point.

Progression of a Wave

Waves begin as ripples (capillary)- wind blowsRipples become chop – small wavesChop becomes organized:• Smaller waves are eaten by larger waves• Faster waves overtake slower waves

Swell- large rolling waves of the deep ocean.• organized, symmetrical wave• the crest and trough are smooth curves of

equal size and shape.

Wave Spectrum

Characteristics of progressive waves:

Parts of a wave are:• Wave crest • Wave troughWave parameters:• Wave height (H)• Wave amplitude (1/2 H)• Wave length (L)• Wave period (P)Wave period provides a basis for classifying waves as capillary

waves, chop, swells, and tsunami

Beaufort Scale

TsunamisCaused by • Seizmic action (earth quakes) • Volcanic action

Tsunamis

• Move outward from center of source• Start in Deep Water (heavy volume & mass)• No high waves until shallower water • Moves faster when in deeper water• closer to land ---- slows down, higher waves

Ocean Currents Move like Rivers

Movement Caused by • Heat energy from sun• Wind Energy• Coriolis effect (rotation

of Earth)

Characteristics: salinity, density, temperature

Gulf Stream:• Along East Coast of USA• Strong, warm, salty

waterHumboldt:• Along West Coast of S.

America• COLD brings minerals,

nutrients to surface

Ocean Currents

• Influence weather and climate by transferring heat from tropical to polar areas

• Distribute nutrients• Scatter organisms (even people)

Currents

• Maintain their paths like rivers• Force of gravity causes dense water to sink,

less dense water rises• Density is influenced by temp and salinity

Spring Tides

Spring Tides

Additive affect of gravity on water• Highest hightides• Lowest low tides

Neap Tide

90 Degree angle of • sun• Earth • MoonAlternate 2 wk intervals

Compare Spring and Neap Tides

Notice that the bulges follow the moon!

Tidal Cycle

Each cycle is 24 hour + 50 minutes (the moon rises 50 minutes later each day!)

Each high tide is about 12 hours apart.Each low tide occurs at mid-point between high tides.

There are 2 high tides and 2 low tides each day.

Storm Surges• An abrupt bulge of water driven ashore by a

tropical storm or storm surge.• Crest of storm surge can go 25 - 40 feet above

sea level• Not measured as wave—only 1 crest

Seiche(pronounced saysh)

• A standing wave in a smaller body of water• First studied in Switzerland’s Lake Geneva• Water level would rise and fall at regular

intervals during wind storms

(Think -------bath tub sloshing!)

Barrier Islands

• A small, thin strip of beach • Parallel to the shore

Some are formed when sediments accumulate on submerged rises parallel to shore

A Typical Barrier Island

Barrier Islands

• Some form when a river deposits sediment over a long period of time.

• A river can change course several times and forme different lobes.

• The Mississippi River Delta is a good example.

Why are Barrier Islands important?

• Protect shoreline from erosion• Barrier against strong storm surges• Provide habitat (land) for wildlife• Separate ocean water from shallow channels

between the barrier island and the shore—making a different habitat for aquatic life.

Cycle of Barrier Island Formation

1. Active Delta2. Abandonment3. Detachment4. Submergence

1. Active Delta

• Delta actively builds land, depositing sediment from the channel to the Gulf of Mexico

2. Abandonment

The delta is no longer active and erosional forces are at work on the headland, forming sandy spits on either side of the old channel.

3. Detachment

The combined effects sea level rise + subsidence (relative sea level rise) cause the barrier to detach-> become an island.

4. Submergence

Rising sea level continuesBarrier island is now more submergedBecomes a shoal beneath the water

5. Reoccupation

If natural conditions prevailed, (they haven’t), the River’s distributions could bring more sediment to build a new delta lobe.

The cycle would continue.