Sunshine StateSTANDARDSSC.D.1.3.1: The studentknows that mechanicaland chemical activitiesshape and reshape theEarth’s land surface byeroding rock and soilin some areas anddepositing them inother areas, sometimesin seasonal layers.

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VOCABULARYlongshore drift p. 275longshore current p. 275sandbar p. 276barrier island p. 276dune p. 277loess p. 278

BEFORE, you learned

• Stream systems shape Earth’ssurface

• Groundwater creates cavernsand sinkholes

NOW, you will learn

• How waves and currents shape shorelines

• How wind shapes land

KEY CONCEPT

Waves and wind shape land.

THINK ABOUT

How did these pillars of rock form?

The rock formations in thisphotograph stand along theshoreline near the small townof Port Campbell, Australia.What natural force createdthese isolated stone pillars?What evidence of this force canyou see in the photograph?

Waves and currents shape shorelines.The stone pillars, or sea stacks, in the photograph above are a majortourist attraction in Port Campbell National Park. They were formedby the movement of water. The constant action of waves breakingagainst the cliffs slowly wore them away, leaving behind pillarlike formations. Waves continue to wear down the pillars and cliffs at therate of about two centimeters (one inch) a year. In the years to come,the waves will likely wear away the stone pillars completely.

The force of waves, powered by wind, can wear away rock andmove thousands of tons of sand on beaches. The force of wind itselfcan change the look of the land. Moving air can pick up sand particlesand move them around to build up dunes. Wind can also carry hugeamounts of fine sediment thousands of kilometers.

In this section, you’ll read more about how waves and wind shapeshorelines and a variety of other landforms.

MAIN IDEA WEBRemember to organizeyour notes in a web asyou read.

ShorelinesSome shorelines, like the one near Port Campbell, Australia, are madeup of steep, rock cliffs. As waves crash against the rock, they wear awaythe bottom of the cliffs. Eventually, parts of the cliffs above break awayand fall into the water, where they are worn down and carried away bythe water.

While high, rocky coasts get worn away, low coastlines often getbuilt up. As you read earlier, when a stream flows into an ocean or alake, it deposits its sediment near its mouth. This sediment mixes withthe sediment formed by waves beating against the coast. Waves andcurrents move this sediment along the shore, building up beaches.Two terms are used to describe the movement of sediment and wateralong a shore: longshore drift and longshore current.

• is the zigzag movement of sand along a beach.Waves formed by wind blowing across the water far from shoremay hit a shoreline at an angle. These angled waves carry sandup onto the shore, and then gravity pulls the water and sanddirectly back into the water. The sand gradually moves down thebeach. The illustration below shows longshore drift.

• A is movement of water along a shore aswaves strike the shore at an angle. The direction of the longshorecurrent can change from day to day as the direction of the wavesstriking the shore changes.

Longshore drift moves large amounts of sand along beaches. It cancause a beach to shrink at one location and grow at another.

longshore current

Longshore drift

Longshore Drift

Walls of rock extend out intothe ocean at Cape May, NewJersey. They were built tokeep beaches from being lostto longshore drift.

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longshore currentIncoming waves push sandup the beach at an angle.

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wave direction

The sand washesback straightdown the beach.

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Sandbars and Barrier IslandsAs they transport sand, ocean waves and currents shape a variety ofcoastal landforms. Longshore currents, for example, often deposit sandalong shorelines. The sand builds up to form sandbars. A is aridge of sand built up by the action of waves and currents. A sandbarthat has built up above the water’s surface and is joined to the land atone end is called a spit. The tip of Cape Cod, Massachusetts, is a spit.

Strong longshore currents that mostly move in one direction mayproduce sandbars that build up over time into barrier islands. A

is a long, narrow island that develops parallel to a coast.barrier island

sandbar

Waves and currents move and build upsand deposits to form a sandbar underthe water surface.

As more sand is deposited, the sandbarrises above the surface to become a barrier island.

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sandbar

barrier island

How does sand move along a beach?PROCEDURE

Prop up a book as shown.

Hold a coin with your finger against the bottom right corner of the book.

Gently flick the coin up the slope of the book at an angle. The coin shouldslide back down the book and fall off the bottom. If necessary, readjust theangle of the book and the strength with which you are flicking the coin.

Repeat step 3 several times. Observe the path the coin takes.Record your observations. Include a diagram that shows the general path the coin takes as it slides up and down the book.

WHAT DO YOU THINK?

• What path did the coin take on its way up? On its way down?• In this model of longshore drift, what represents the beach,

what represents the sand, and what represents a wave?

CHALLENGE In this model, in which direction will the long-shore current move? How could you change the model to change the direction of the current?

4

3

2

1

Longshore DriftLongshore DriftSKILL FOCUSObserving

MATERIALS• 2 or 3 books• coin

TIME15 minutes

Chapter 8: Erosion and Deposition 277

A barrier island gets its name from the fact that it forms a barrierbetween the ocean waves and the shore of the mainland. As a barrierisland builds up, grasses, bushes, and trees begin to grow on it.

Barrier islands are common along gently sloping coasts around theworld. They occur along the coasts of New Jersey and North Carolinaand along the coastline of the Gulf of Mexico. Padre Island in Texas isa barrier island about 180 kilometers (110 mi) in length.

Barrier islands constantly change shape. Hurricanes or other stormscan speed up the change. During large storms, waves can surge acrossthe land, carrying away huge amounts of sediment and depositing itelsewhere. Houses on beaches can be destroyed in storms.

Check Your Reading How and where do barrier islands form?

Wind shapes land.At Indiana Dunes National Lakeshore, not far from the skyscrapers of Chicago, you can tumble or slide down huge sand dunes. First-timevisitors to the Indiana dunes find it hard to believe that sand forma-tions like these can be found so far from a desert or an ocean. Whatcreated this long stretch of dune land along the southern shore ofLake Michigan? The answer: wind. A is a mound of sand builtup by wind.

Like water, wind has the power to transport and deposit sediment.Although wind is a less powerful force of erosion than moving water,it can still shape landforms, especially in dry regions and in areas thathave few or no plants to hold soil in place. Wind can build up dunes,deposit layers of dust, or make a land surface as hard as pavement.

dune

This lighthouse on a barrier island in NorthCarolina had to be movedbecause of beach erosion.The photograph showsthe lighthouse before itwas moved.

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Dune FormationEven a light breeze can carry dust. A moderate wind can roll and slidegrains of sand along a beach or desert, creating ripples. Only a strongwind, however, can actually pick up and carry sand particles. When thewind dies down or hits something—such as a cliff or a hill—it dropsthe sand. Over time, the deposits of sand build up to create dunes.

Some dunes start out as ripples that grow larger. Others form aswind-carried sand settles around a rock, log, or other obstacle. In climates with enough rainfall, plants begin to grow on dunes a shortdistance from beaches.

Dunes form only where there are strong winds and a constant supply of loose sand. They can be found on the inland side of beachesof oceans and large lakes, on the sandy floodplains of large rivers, andin sandy deserts.

Dunes can form in a variety of sizes and shapes. They can reachheights of up to 300 meters (about 1000 ft). Some dunes are curved;others are long, straight ridges; still others are mound-shaped hills.A dune usually has a gentle slope on the side that faces the wind and a steeper slope on the side sheltered from the wind.

LoessBesides forming dunes, wind also changes the soil over large regions ofEarth by depositing dust. A strong windstorm can move millions of tonsof dust. As the wind dies down, the dust drops to the ground. Depositsof fine wind-blown sediment are called (LOH-uhs).

In some regions, deposits of loess have built up over thousandsand even millions of years. Loess is a valuable resource because itforms good soil for growing crops.

loess

These hills of sand are atthe Great Sand DunesNational Monument inColorado.

Wind makes sand particles build up and tumble down,causing a dune to migrate, or move.

dune movement

wind

sand-particlemovement

Loess covers about 10 percent of the land surface of Earth. Chinahas especially large deposits of loess, covering hundreds of thousandsof square kilometers. Some of the deposits are more than 300 meters(about 1000 ft) thick. Such thick deposits take a long time to develop.Some of the loess deposits in China are 2 million years old. Windsblowing over the deserts and dry regions of central Asia carried thedust that formed these deposits.

Parts of east central Europe and the Mississippi Valley in the UnitedStates also contain significant loess deposits. In the central United States,loess deposits are between 8 and 30 meters (25 and 100 ft) thick.

Desert PavementNot only does wind shape land surfaces by depositingdust; it also shapes land surfaces by removing dust. Whenwind blows away all the smallest particles from a mixtureof sand, silt, and gravel, it leaves behind just a layer of stonesand gravel. This stony surface is called desert pavementbecause it looks like a cobblestone pavement. The coarsegravel and rocks are too large to be picked up by wind.

Check Your Reading How are both loess and desert pavement formed by wind?

Chapter 8: Erosion and Deposition 279

KEY CONCEPTS1. What kinds of landforms do

longshore drift and longshorecurrents produce?

2. How do dunes form?

3. How does loess form, and why is it important?

CRITICAL THINKING4. Identify Cause and Effect

Is longshore drift the cause oreffect of a longshore current?Explain.

5. Predict What effect would abarrier island have on theshoreline of the mainland?

CHALLENGE6. Hypothesize The south and

east shores of Lake Michiganhave large areas of sanddunes, but the north and west shores do not. Write ahypothesis that explains why.You might want to use a mapand draw the shape of LakeMichigan to explain.

This loess deposit in Iowabuilt up over many thou-sands of years.

Desert pavement is made up of particles too large to be picked up by wind.