Wave ActionWave Action

Wave ActionWave Action

• Wave: the movement of energy Wave: the movement of energy through a body of waterthrough a body of water

• Waves are formed when the wind Waves are formed when the wind blows across the water’s surface and blows across the water’s surface and transfers its energy to the water.transfers its energy to the water.

Ocean WavesOcean Waves

Waves occur on the Lake Superior, Waves occur on the Lake Superior,

too!too!

Wave SizeWave Size

• Wave size depends on three things:Wave size depends on three things:

* Strength of the wind* Strength of the wind

* Length of time that the wind blows* Length of time that the wind blows

* Distance the wind travels* Distance the wind travels

Wave EnergyWave Energy

• The energy of the wave can be The energy of the wave can be moved from the middle of the ocean moved from the middle of the ocean to the shore, but the water molecules to the shore, but the water molecules will not end up at the shore.will not end up at the shore.

• The energy transfers, the water The energy transfers, the water molecules remain the same.molecules remain the same.

Water Molecule motion during Water Molecule motion during a wavea wave

• Water particles move in a circular pattern Water particles move in a circular pattern in the upper portions of the water.in the upper portions of the water.

• The deeper you get, the less the circular The deeper you get, the less the circular motion.motion.

• Eventually you get deep enough that the Eventually you get deep enough that the circular motion stops.circular motion stops.

• This is why sunken treasure never movesThis is why sunken treasure never moves

Water motionWater motion

Wave CharacteristicsWave Characteristics

• Crest – top of the waveCrest – top of the wave

• Trough – bottom of the waveTrough – bottom of the wave

• Wave Height – from the bottom of Wave Height – from the bottom of the trough to the top of the crest the trough to the top of the crest (just like your height)(just like your height)

• Wave Length – horizontal distance Wave Length – horizontal distance between crestsbetween crests

How do Waves Change near How do Waves Change near the Shore?the Shore?

• Breakers – white capped waves that Breakers – white capped waves that crash onto the shorecrash onto the shore

* In deep water -> waves travel as long,* In deep water -> waves travel as long,

low waves called swells.low waves called swells.

* In shallow water near the shore -> wave* In shallow water near the shore -> wave

height increases, wavelength height increases, wavelength decreasesdecreases

and breakers are created.and breakers are created.

TsunamisTsunamis

• Tsunamis are waves caused by an Tsunamis are waves caused by an earthquake beneath the ocean floorearthquake beneath the ocean floor

* Most common in the Pacific Ocean.* Most common in the Pacific Ocean.

* Alaska, Hawaii and the Pacific * Alaska, Hawaii and the Pacific

Northwest (Oregon and Washington) Northwest (Oregon and Washington)

are the United States’ main concernsare the United States’ main concerns

* December 26, 2004 – Indian Ocean * December 26, 2004 – Indian Ocean

tsunami that killed over 200,000 tsunami that killed over 200,000 peoplepeople

TsunaTsunamimi

tsunami demo

How do waves affect the How do waves affect the shore?shore?• Longshore Drift (Longshore current)Longshore Drift (Longshore current)

– Waves come into the shore at an angle, Waves come into the shore at an angle, not straight into the shorenot straight into the shore

– When the wave goes back out, it pulls When the wave goes back out, it pulls sediments with it.sediments with it.

– Waves go back in again, but the Waves go back in again, but the sediments are moved slightly down the sediments are moved slightly down the beachbeach

– Moves sediment slowly but constantly Moves sediment slowly but constantly down the beach.down the beach.

Rip CurrentsRip Currents

• Rip Currents are a rush of water that Rip Currents are a rush of water that flows rapidly back to sea through a flows rapidly back to sea through a narrow openingnarrow opening– They can be very dangerous, but narrow They can be very dangerous, but narrow – If you find yourself caught in one, you If you find yourself caught in one, you

should swim parallel to the shore to should swim parallel to the shore to avoid the current, then swim inland.avoid the current, then swim inland.

Escape a Rip CurrentEscape a Rip Current

Waves Causing Beach Waves Causing Beach ErosionErosion• Every minute of every day, the waves are Every minute of every day, the waves are

constantly eroding the beaches. They constantly eroding the beaches. They move sediments from one place to the move sediments from one place to the other. It becomes even worse when a other. It becomes even worse when a storm is present.storm is present.

• Local beaches have to compensate for the Local beaches have to compensate for the removal of sand by off shore dredging.removal of sand by off shore dredging.

• How do the beach communities pay for How do the beach communities pay for this replacement process?this replacement process?

Examples of Beach ErosionExamples of Beach Erosion

Erosion Erosion after Hurricanesafter Hurricanes

Questions – Section 13-1Questions – Section 13-1

1.1. How do waves form?How do waves form?2.2. Why does an ocean buoy bob up and Why does an ocean buoy bob up and

down in the ocean?down in the ocean?3.3. How do wavelength and wave height How do wavelength and wave height

change as a wave enters shallow water?change as a wave enters shallow water?4.4. Using what you know about wave height Using what you know about wave height

and wave length of tsunamis, propose and wave length of tsunamis, propose and explanation of why tsunamis can and explanation of why tsunamis can cause so much damage when they reach cause so much damage when they reach the shore.the shore.