Marine Science Chapter Four: Waves and Tides

Explain orbital motion

Waves carry energy, but do not transport water. As the energy moves through the water, the water particles move up and down in an orbital motion. The energy moves forward, but the water particles move back down under its original position and eventually returns.

What is wave dissipation, and what are restoring forces?

Waves do not carry energy forever; the energy is dissipated, and the water molecules stop moving because of restoring forces. A restoring force is something the returns water to its undisturbed state. Two examples are surface tension (small capillary waves), and gravity (larger waves)

Progressive wind waves

Waves that are started by wind, restored by gravity, and move in a particular direction.

Standing waves

Waves that do not progress on a particular direction, but rather form around a node/ an enclosed body of water. Antinodes= the high and low points of the water

What happens as a result of landslides?

When a giant piece of land or ice enters the ocean, it moves water away. As it sinks, the water that was displaced moves back to its original position. This movement creates a series of waves that moves away from the location where the material originally entered the water.

Where are the most favorable conditions for wave formation?

40 S and 50 S. Large and open, few landmasses to limit fetch.

Because the moon is the dominant cause of tides...

A tidal cycle is the same length as a lunar cycle

Diurnal tide

A tidal cycle of one high tide and one low tide per day.

semidiurnal tide

A tidal cycle of two high tides and two low tides each lunar day, with the high tides of nearly equal height.

Crest

Highest point of a wave

Wavelength

Horizontal distance between the crests or between the troughs of two adjacent waves

Wave reinforcement

If the crests of two waves collide, however, they add together to produce a higher wave.

Rip Currents

Areas of rapid seaward-flowing water

Two categories of waves

Deep water and shallow water; also intermediate

Shallow water?

Depth, not wavelength

What is the period of the wave determined by?

Determined by generating forces; so even as the wave move, its period does not change

Trough

Lowest point of a wave

What happens when the smooth surface of the water is disturbed?

More energy is transferred from the air to the water, and it becomes easier for the wind to grip the water. Larger waves are formed. If the wind continues to blow, the peaks of the waves are pushed up, and the troughs are stretched. The larger waves move away from their source slightly faster than the wind that formed them.

What are swells?

Differ from other progressive wind waves in that they are evenly spaced waves with smooth rounded crests and troughs. They start out as progressive wind waves, but as they eventually settle into evenly spaced waves, the shorter waves dissipate and only long waves carrying large amounts of energy are left. They carry energy very long distances across ocean basins

Why are there two high tides and two low tides?

Earth takes 24 hours to complete a rotation.

Longshore Transport

The movement of water or sediment down a shore in the direction of wave action.

wave frequency

The number of waves passing a fixed point per second.

Where is the Moon's pull the strongest? Where is it the weakest?

The pull is the strongest on the side that is facing the moon. The moon's gravity pulls the water towards the moon. On the opposite side of the earth, the pull is weaker. The water bulges away from the moon because of centrifugal force.

What are capillary waves?

The smallest of wind driven waves. Also called ripples.

Height of a wave

The vertical measurement from the trough to the crest of a wave

What do tides affect?

They don't affect the middle of ocean basins, but rather nearshore areas.

What happens to capillary waves as the wind continues?

They grow bigger, and the surface of the water becomes rougher.

What happens after the waves move away from the wind or storm that formed them?

They settle into swells.

Equilibrium

Undisturbed ocean level

How is wave speed determined

Wavelength and wave period

In deep water, wave speed is dependent on...

Wavelength, not depth

Wave refraction

Waves are refracted as they move from deep water to shallow water at an angle.

Generating Forces of Waves

Waves are started by disturbances. The three main ones are wind, earthquakes, and landslides

What are tsunamis, and what causes them?

When the seafloor is disturbed, the water above it moves up or down with it- causing a large amount of water to be displaced. The water moves away from from the source of the earthquake. These waves can travel long distances and cause great damage to coastal areas. Are not produced with every earthquake, and can be very hard to track.

How do capillary waves form?

Wind blows across the surface of a body of water, and it creates friction between the air and the water.

What three factors is wave height dependent on?

Wind speed, fetch, and duration. The largest waves are formed when all three are maximized

What factors influence the formation of waves?

Wind speed, fetch, duration of wind, and water depth

Internal Waves

formed at density boundary between 2 different water masses (water and water). Where they meet, they oscillate and form an underwater wave. Vary greatly in wavelength and periods.

Where are the largest tidal ranges seen?

narrow basins

wave cancellation

occurs when the crest of one wave meets the trough of another, and the sea surface ends up intermediate between the two

Flood Tide

rising tide

What causes tides?

the gravitational pull of the moon and sun, and the rotation of the sun, moon, and earth.

Wave period

the time required for corresponding points on consecutive waves to pass a given point

Tidal Bores

waves that form when inflowing tidal water is slowed by outflowing river water

Deep water waves

waves that move in water deeper than one-half their wavelength; speed depends on wavelength; form from swell waves

What causes neap tides?

when the sun and moon are at right angles to each other, (the solar tide partially cancels out the lunar tide and produces moderate tides) Occurs during quarter moons

What are the two types of wave energy?

Potential: Height of the wave, energy from its position above the surface Kinetic: Motion of the water particles, energy of the objects in motion

What are the three tidal patterns?

Semidiurnal Diurnal Mixed

Are waves more easily produced in areas with shallow or deep water?

Shallow

What causes spring tides?

Sun and moon are aligned. They happen during a new moon and a full moon

What has the strongest gravitational pull on the oceans?

The Moon

What is fetch?

The distance of open water that the wind can blow across without changing distance. Areas that have a large fetch will produce more waves than areas with a smaller fetch. Similarly, the wider the fetch, the more waves that can form.

Highwater

The highest level that a tide can rise

Tides vary because of....

The land and the seafloor.

Low water

The lowest point to which a low tide falls.

Why does centrifugal force arise?

The moon does not revolve around the earth. They rotate together. This is called the earth-moon system.

Mixed semidiurnal tides

a tidal pattern with two high tides and two low tides of different heights each day

Half the height of a wave

amplitude

Shallow water waves

are waves in water shallower than 1/20 their original wavelength; as deep water waves approach the coast, the patterns of the orbits change into flattened circles (ellipses); this friction causes the waves to slow down and creates a shorter wavelength; waves break and spill over, creating surf

Ebb tide

falling tide