Unit 11 Lesson 2 How Does Ocean Water Move? Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 11 Lesson 2 How Does Ocean Water Move?

Copyright © Houghton Mifflin Harcourt Publishing Company




Catch a Wave


• A wave is the up-and-down movement of surface water.

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Catch a Wave


Catch a Wave



Catch a Wave


• Surface waves are caused by wind pushing against the surface of the water.

• Waves constantly affect the shoreline. Even gentle waves weather and erode rock and transport sand.

• Powerful hurricane winds produce much larger waves, which can cause a storm surge, or an unusually high water level.


Catch a Wave



Catch a Wave



Catch a Wave


• Energy in waves can be converted into electrical energy.

• This electrical energy can provide a steady source of electricity, since wave motion never stops.


Go with the Flow


• An ocean current is a steady flow of water in a regular pattern in the ocean.

• Steady winds• temperature • water salinity• the shape of both

ocean floor and shoreline.

• play a role in driving currents.



Go with the Flow


• Ocean currents can have predictable effects.

• For example, the Gulf Stream is warm Atlantic Ocean water that runs south to north along the eastern coast of North America.

• The warm Gulf Stream helps make weather in Europe warmer than in other places that are as far north.


Go with the Flow



Go with the Flow


• Water steadily flowing from the shore against incoming waves is called a rip current.


Go with the Flow



Go with the Flow


• Sometimes, water in the South Pacific gets unusually warm, producing a climate pattern called El Niño.

• An El Niño season disrupts normal weather patterns, causing extreme weather, such as droughts and flooding throughout the world.


Go with the Flow



The Turning Tides



The Turning Tides


• The water level of the ocean rises and falls in a cycle called a tide.

• Tides are caused by the “pull” of the sun and moon on Earth’s oceans.



The Turning Tides


• The moon’s gravity pulls on Earth, resulting in two bulges forming in Earth’s oceans.

• The higher water level in the bulges produces a high tide. The lower water level, or low tide, occurs between the bulges.


The Turning Tides


• When Earth, the sun, and the moon are in a straight line, their combined gravity causes the highest high tides and the lowest low tides.

• When the sun, Earth, and the moon are positioned in an “L” shape, the difference between the levels of high tide and low tide is the smallest.


The Turning Tides


• The relative positions of the sun, moon, and Earth affect the heights of tides.


The Turning Tides



The Turning Tides



Changing Shorelines


• Land at the edge of the ocean is called shore.

• Waves and ocean currents carry sand to and away from the shore. The same wind that drives the waves also causes rocks and cliffs to weather.

• The ocean can carry sand from beaches in a short time. A big storm can erode a beach in a day.



Changing Shorelines


• People can restore the beach by replacing and stabilizing the sand and by building structures.

• A jetty is a structure, often made of piles of rock, that a current cannot move.

• Jetties preserve beaches and keep sand from accumulating and making waterways too shallow for boats.



Changing Shorelines





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Unit 11 Lesson 2 How Does Ocean Water Move? Copyright © Houghton Mifflin Harcourt Publishing Company