Ocean Waves, Currents, and TidesOcean Waves, Currents, and Tides

Mr. WoodhamMr. Woodham

66thth Grade Earth Science Grade Earth Science

Marshall Middle SchoolMarshall Middle School

WavesWavesThe four parts of a wave:The four parts of a wave:

WavelengthWavelength

TroughTrough

Wave HeightWave Height

CrestCrest

WavesWavesCheck What You Check What You THINKTHINK You Know You Knowwavelength, wave height, trough, crestwavelength, wave height, trough, crest

_____2_____

1

3

4

Check What You Check What You THINKTHINK You Know You Knowwavelength, wave height, trough, crestwavelength, wave height, trough, crest

What is the horizontal distance between What is the horizontal distance between crests ?crests ?

What is the lowest part of the wave?What is the lowest part of the wave?

What is the highest part of the wave?What is the highest part of the wave?

What is the vertical distance between What is the vertical distance between crest and trough?crest and trough?

Diagram of a WaveDiagram of a Wave

WavesWaves

Waves start in the open oceanWaves start in the open ocean

The size of a wave depends on the strength of the wind, the length of The size of a wave depends on the strength of the wind, the length of time that it blows, and the distance over which it blows time that it blows, and the distance over which it blows

Waves move energy, not water. The water in a wave does not actually Waves move energy, not water. The water in a wave does not actually move forward, just the energy generated by the wind.move forward, just the energy generated by the wind.

The wind affects the water at the surface more than it does the deep The wind affects the water at the surface more than it does the deep water.water.

Let’s take a look at this in action: Let’s take a look at this in action: Wave Energy and Wave Size

BreakersBreakers As waves approach the shore, the water becomes shallower.As waves approach the shore, the water becomes shallower. The bottom of the waves begin to touch the sloping ocean floor.The bottom of the waves begin to touch the sloping ocean floor. Friction between the ocean floor and the water causes the waves toFriction between the ocean floor and the water causes the waves to

slow down.slow down. As the speed of the wave slows down the shape of the wave begins As the speed of the wave slows down the shape of the wave begins

to changeto change Near the shore wave length decreases and wave height increases.Near the shore wave length decreases and wave height increases. When the wave reaches a certain height, the crest of the wave When the wave reaches a certain height, the crest of the wave

topples.topples.

How Waves Affect theHow Waves Affect the ShoreShore

Longshore DriftLongshore Drift

As waves come ashore, water washes up the beach at an angle, As waves come ashore, water washes up the beach at an angle, carrying sand grains.carrying sand grains.

Gravity causes the water and the sand to run straight back down the Gravity causes the water and the sand to run straight back down the beach slope.beach slope.

Longshore Drift 1

Longshore Drift 2Longshore Drift 2

Longshore Drift 3Longshore Drift 3

Barrier IslandsBarrier Islands Barrier islands like the one’s that stretch along the coast of Barrier islands like the one’s that stretch along the coast of

Georgia are formed from deposition of sediments coming Georgia are formed from deposition of sediments coming from Georgia’s rivers, and sand being deposited along the from Georgia’s rivers, and sand being deposited along the coastal side of the island by the longshore drift.coastal side of the island by the longshore drift.

Because the wind and waves are constantly redistributing Because the wind and waves are constantly redistributing the sand these islands are not permanent. the sand these islands are not permanent.

They are constantly being reshaped.They are constantly being reshaped.

Let’s see what you have Let’s see what you have REALLY learned!REALLY learned!

wavelength, wave height, trough, wavelength, wave height, trough, crestcrest

1

_____2_____

3

4

Let’s see what you have Let’s see what you have REALLY learned!REALLY learned!

What is the horizontal distance between crests?What is the horizontal distance between crests?

What is the lowest part of the wave?What is the lowest part of the wave?

What is the highest part of the wave?What is the highest part of the wave?

What is the vertical distance between crest and What is the vertical distance between crest and trough?trough?

Currents

A current is a large stream of water that flows through the ocean

Two types of currents

Surface Currents Deep Currents

Surface Currents Driven mainly by the wind They follow Earth’s major wind patterns which move in a circular

pattern

Earth's wind and current patterns

Why do the winds and the currents move in a circular pattern?

The Coriolis Effect

(Globe Demo)

Surface Currents Due to the Coriolis effect, currents in the Northern Hemisphere

curve to the right and to the left in the Southern Hemisphere.

The largest and most powerful surface current in the North Atlantic Ocean, the Gulf Stream, is caused by strong winds that blow regularly from the west. It carries more than 100 times the water of the mighty Mississippi river. It carries warm water from the Gulf of Mexico northward along the east coast of the U.S. As a result of the Coriolis effect, it curves north east across the Atlantic

Surface Currents A surface current warms or cools the air above it, influencing the

climate of the land near the coast.

Because of the warm waters of the Gulf Stream, a country as far north as England can have fairly mild weather.

The average winter temperature in Newfoundland, Canada is

15°F. In England the average winter temperature is 42°F. That’s a difference of 27°, all due to the Gulf Stream.

Surface Currents

Surface Currents

At certain places on Earth, sometimes the wind patterns reverse, causing the surface currents to reverse directions.

One such reversal called El Niño happens about every 2 to 7 years and lasts for 1 to 2 years at a time.

El Niño starts when the wind pattern which usually blows towards the west reverses and blows east across the Pacific Ocean bringing warm waters with it.

Of course, this warm current warms the air above it causing more evaporation and therefore more storms for the western U.S. creating heavy rains, flooding, and mudslides in California and more tornadoes in Florida.

El Niño

Deep Currents Deep currents are caused by differences in the density of ocean water. Ocean water density depends on its temperature and its salinity. Cold water is more dense than warm water. Saltier water is more dense than less saltier water. (Demos) As warm surface currents near the poles the water cools and its salinity increases due

to ocean water freezing and leaving the water near the poles more salty. (Page 384) The cold, saltier water sinks and starts moving back towards the equator along the

bottom of the ocean. When the water reaches the equator, it warms and rises again. -Someone tell me what this self-powered system of cold water sinking and warm

water rising is called? A C_ _ _ _ _ _ _ _ N C _ _ _ _ _ _ T

Deep currents flow slowly. They may take as long as 1,000 years to flow from pole to equator and back again.

Deep Currents

Currents

Coriolis effect El Niño warmer Surface

direction evaporation 100 Gulf Stream

_______________ ocean currents are caused mainly by winds thatblow regularly in the same ___________. They can reach depths ofseveral _____ meters. The largest and most powerful surfacecurrent in the North Atlantic Ocean is the __________ __________. This current takes a right turn east across the Atlantic due to the ______________ ____________. It warms the air above it, causingit to be _________ in England than it is in Nova Scotia, even thoughboth of them are at the same latitude. Sometimes surface currentsreverse, like the __________ ___________. When this happens, thereis more ____________________, leading to more storms for the U.S.

Currentsconvection current salinity heat

equator density temperature saltier

Deep ocean currents are caused by differences in the __________of ocean water. The density of ocean water depends on its____________________ and _______________. As deep ocean currents reach the poles the water cools and gets ______________which makes it denser causing it to sink. This cool water thenflows across the bottom of the ocean back to the ______________where it is warmed again starting the _____________ ___________over again. This is the way that ___________ is distributed aroundthe globe.

Tides Tides are the daily rise and fall of Earth's waters on its

coastlines

When water on the coast reaches its highest point it is high tide. When water on the coast reaches its lowest point it is low tide. Unlike surface waves, tides are regular and do not depend on wind.

If not wind, then what causes tides?

Tides are caused by the interaction between the Earth, the moon, and the sun.

The gravity exerted on Earth's oceans by the moon and the sun cause the water to move from one side of the planet to the other side.

The moon is much closer to the Earth than the sun, so it exerts a greater gravitational effect on the tides.

Gravitational effects of the moon and the sun on tidesMore

TidesThere are two high tides and two low tides about every 25 hours.That means every six or so hours you have a high tide and then a bit more than six hours later you have a low tide.Changes in the positions of Earth, the moon, and the sun affect the heights of tides during a month.

If it is 7:45 A.M. in the photo on the left, what time is it in the photo on the right if it is still the same day? What time will the next high tide be?

Tides

The sun is much bigger than the moon. Why doesn't the sun affect

tides more than the moon?

Why do the heights of the tides change during the course of a month?

Is the water higher during a neap tide or a spring tide?

If the low tide at location A occurs at 3:00 P.M., at what times will the

next two low tides occur?

Lab Zone Discover Activity on page 366 of your textbook.