how does water change earth's surface? · these processes change earth's surface and,...

Level A reading coming soon.

How Does Water Change Earth's Surface?

ScienceVocabulary

glacier

minerals

sediment

sedimentary rock

H O W D O E S W A T E R C H A N G...

© 2020 Teachers' Curriculum Institute Level: A

Weathering, erosion and deposition are changing Earth'ssurface all around you. Water is an important cause ofthese changes. You will learn that water changes Earth'ssurface in different ways. Some of these changes are easyto observe because they happen quickly. But sometimesthese changes happen over millions of years!

1. Rainwater CausesWeathering and ErosionYou learned that water can weather rock and erode soil.These processes change Earth's surface and, when a lotof water is flowing, these changes can happen fast.

Think about the last time there was a storm where you live.During a storm, rainwater can erode soil very quickly. Youmight see splashing rain drops, moving soil on a bare spotof ground. When the rainwater hits the soil, it loosens thesoil at the surface. This is the beginning of erosion. Thewater splashes bits of soil and small rocks and starts toflow downhill. When it rains enough, small streams start toform. Eventually, small streams join together into largerstreams and then rivers. The force of this water carries bitsof rock and soil along with it. So, within minutes or hours, aheavy storm can cause a lot of erosion.


Level: A © 2020 Teachers' Curriculum Institute

Rainwater flows downhill after arainstorm, collecting into everlarger streams and rivers. Theforce of the water erodespreviously weathered material. Italso grinds down and weathersthe rock it flows over.

Rainwater can also weather rock. Think about the streamduring a heavy rainstorm again. As the water rushes overthe ground, the bits of sand and soil that it carries slowlygrind down the rock they flow over. Some of the rainwateralso flows down into the soil and rock. Very slowly, thewater mixes with some of the minerals in the rock and soil.Minerals are the chemicals that rock is made out of.Because the minerals are mixed with the water, they arecarried away as the water flows. The movement of theseminerals changes the structure of the rock. In these ways,rainwater weathers rock.

2. Rainwater CausesDeposition



When rainwater slows down ordries, it can deposit a layer ofmud that can crack as it dries.

Over time, rain weathers rock. It also erodes largeamounts of material. What happens to the eroded bits ofrock and soil?

The rainwater carrying sand, rock, and soil will eventuallystop moving. When the water stops moving, it deposits thesand, rock, or soil in new areas. These small pieces ofsand, rock, and soil are now sediment. Sediment is anyeroded material, such as weathered rock, sand, and soil,that is deposited in a new place.

As the rain slows, the rainwater flowing over the groundstarts to slow down. Usually, larger pieces of materialsettle and are deposited first. During a heavy rainstorm,you might see a small layer of rocks on the sidewalk. Asthe rain turns into a drizzle or stops completely, the waterdeposits the smaller pieces of material such as sand orsoil.



Deposition Makes Layers

Sometimes rainwater deposits sediment in more than onelayer. After a storm, you might see a layer of dried mudcovering some of the sidewalk or street. This mud is madeof many tiny pieces of sediment. If it rains again severaldays later, a new layer of sediment will be deposited on topof the first layer. The new layer might be made of adifferent type of sediment. So, you might see differentcolors or textures from the original layer of mud.

Flooding waters erode weathered material, moving it downhill. The waterdeposits this material as sediment in new areas, often along the banks of thestream.

3. Deposition Helps FormNew Rocks



Sedimentary rock forms whenlayers of sediment are pressedtogether into one solid piece.Sedimentary rock, like thissandstone, often shows thoselayers.

Suppose you are at the Grand Canyon. You may noticethat it is made of many layers of different colored rock.Where did these layers come from?

These layers of rock were formed by deposition. Much ofthis material was deposited by water at different times.Some of the rocks in the Grand Canyon are 2 billion yearsold!

Remember how rainwater can deposit layers of sedimentalong the sidewalk? On some places on Earth, the samething happens on a much larger scale. Many large riversdeposit huge amounts of sediment where they slow downor reach the sea. After many years, these sediments canadd up to form a deep layer. Sometimes the environmentchanges, and a new kind of sediment starts beingdeposited. This forms a different layer. New layers always



form on top of the older layers.

As more sediment is deposited, the sediment is buried andchanges over time. Sediment is heavier than water. Thelayers on top push down on the layers beneath them, andthe pieces of rock and soil get smashed together. Mineralsfrom the water can act like glue to help the pieces sticktogether. Eventually, the material can become solid rock.Rock that is formed from deposited sediment is calledsedimentary rock. Many of Earth's surface rocks aresedimentary rocks.

Over time, deposited sediment can add up to form deep layers. As these layersare buried, they very slowly turn into a type of stone called sedimentary rock.Many layers of sedimentary rock can be seen in the Grand Canyon.

Nature of Science



Nature of Science

4. River WaterWeathers andErodes

The Grand Canyon was formedover millions of years. First,sediment was deposited inlayers. The layers pushed oneach other and formedsedimentary rock with thepressure. Then the ColoradoRiver weathered and eroded therock to form a canyon.

Weathering, erosion, and deposition can happen veryquickly, but it usually takes a long time for them to changea whole landscape. The Grand Canyon was carved bythese processes, but it took millions of years.

A canyon is a deep valley carved by water in an area ofrock. The Grand Canyon is one of the deepest canyons in



the world. At the bottom of the Grand Canyon flows theColorado River. Millions of years ago, this river startedflowing and weathering the rock in the area.

Weathering alone cannot carve a canyon. Erosion mustalso happen. As the Colorado River carried huge amountsof sediment from the canyon to the ocean, the watereroded the rock. Most scientists think it took about 6 millionyears for the river to weather and erode the whole GrandCanyon. Recently, other scientists found new evidencethat the canyon might be over 17 million years old.Scientific explanations can change and improve with newevidence.

Erosion and weathering can make an area look completelydifferent. The Colorado River still runs through the GrandCanyon, deepening it over time.

5. Ice Causes Weatheringand Erosion



Over time, freezing and thawingice can break apart even verystrong rocks, like this one inAntarctica. Liquid water, wind,and gravity help erode theweathered materials.

You learned how liquid water can cause material onEarth's surface to weather, erode, and be deposited.Frozen water can also cause these changes on Earth'ssurface.

One way ice can weather rocks is with ice wedging. Icewedging is a process in which cracks in a rock get biggerfrom water inside them freezing. Ice wedging happensbecause water takes up more space as it freezes into ice.

First, a rock with a crack in it fills up with liquid water fromrain or some other source. Then the temperature dropsbelow freezing. The water starts to freeze and expand. Icetakes up more space than liquid water. The expanding icepushes against the inside of the crack. It spreads the sidesof the rock apart and makes the crack bigger. When theweather warms up, the ice melts. Since the crack is nowlarger, more water can get in and freeze. This patternrepeats. Each time the water freezes, it expands, and the



crack gets bigger.

Erosion also happens with ice wedging. The ice wedgingcauses bits of rock to break off. These pieces that the icebreaks off do not always stay in the crack. Often themelted ice, rain, or other sources of water carry these bitsof rock away from the crack. Gravity can make the piecesfall out too. In these ways, the weathered rock erodes.

6. Glaciers CauseWeathering, Erosion, andDeposition



Glaciers are huge rivers of ice.They move very slowly, slowerthan you can see. But their forcescrapes off huge amounts of rockand moves it to new places.

Glaciers are another way ice weathers and erodes rock.They also move weathered rock and deposit it assediment. This happens in high mountain valleys and incold places like Antarctica.

Ice from glaciers starts out as snow. A glacier is a slowlymoving river of ice. Glaciers form where it is so cold thatnot all of the snow melts in the summer. Over time, somuch snow piles up that it gets pressed and stickstogether. This forms a glacier.

Very slowly, the glacier flows down the mountain. Glaciersweather and erode rock as they flow down valleys.Glaciers are slow, but they are so large that they create a



lot of force. The weight of the ice scraping along theground grinds off large amounts of rock underneath them.This weathered material moves downhill with the glacier.Large glaciers carve out whole valleys and change the V-shape of river valleys to a U-shape. A U-shaped valley isevidence there once was a glacier flowing through thevalley.

Glaciers deposit large amounts of rock, sand, and mud attheir bases. The glacier carries its sediment down thevalley to lower elevations, where it is warmer. This part ofthe glacier starts to break off and melt. Here, it deposits thesoil and rocks that it carried. This is usually manykilometers from where the glacier started.



Glaciers weather and erode the land where they flow. Over thousands of years,they can create a U-shaped valley like this one. The shape of this valley isevidence that there used to be a glacier here.

LESSON SUMMARY

How Does Water Change Earth's Surface?



1. Rainwater Causes Weathering and Erosion A stormcan cause erosion quickly. Raindrops loosen and movesoil, eroding it. As the rain forms larger streams, theforce of the water increases. The sediment in the waterflows over rocks, wearing it down.

2. Rainwater Causes Deposition When flowing waterslows down or stops, the soil and sand it carrieseventually stop moving. These small pieces of rock arethen deposited as sediment. Over time, different layersof this sediment form on top of one another.



3. Deposition Helps Form New Rocks Where a lot ofsediment is deposited, the lower layers are squeezed bythe weight of the layers above. Eventually they turn intosedimentary rock. Most of Earth's surface rocks on itscontinents are sedimentary rocks.

4. River Water Weathers and Erodes As rivers flow, theyweather and erode the rock they move over. Millions ofyears of this can produce large canyons, like the Grand



Canyon in the southwestern United States.

5. Ice Causes Weathering and Erosion Ice wedginghappens when water gets in the cracks of a rock andfreezes. The freezing water pushes the sides of the rockapart. Over many cycles of freezing and melting, icewedging can crack rocks apart.

6. Glaciers Cause Weathering, Erosion, and Deposition



Glaciers are huge rivers of ice. The weight and power ofthe slow-moving ice scrapes off rock, erodes it, anddeposits the pieces as sediment further downhill. Thiserosion carves U-shaped valleys.

SUPER SIMPLE SCIENCE

Dripping Water Did That!

Weathering and erosion can create deep canyons andhuge caves. Water also causes special kinds of depositionin caves deep underground. These look like delicate worksof art. How does water create sculptures out of rock?

This room inside CarlsbadCaverns, New Mexico, is calledthe Chinese Theater.

Each year, thousands of people visit huge caves. Theytravel from all over the world for a chance to adventurethrough maze-like passages. Jewel Cave in South Dakotaand Mammoth Cave in Kentucky are two of the longestcaves in the world. You could walk for more than a



hundred kilometers in each! But people do not visit theseunderground worlds to see how far they can walk. Believeit or not, they are there to see deposition.

These huge caves and others like them, such as OregonCaves in Oregon and Carlsbad Cavern in New Mexico, arenowhere near one another. And they are found in verydifferent climates. Even so, they are all formed of the samematerial—limestone. Deposition in limestone caves is morethan just layers of clay or sand. Cone-shaped rocks stickup from the floor. Some cones hang from the ceiling. Thereis also stone shaped like curtains, columns, icicles, ordrinking straws. All of these forms are created by water,one drop at a time. Visitors of the caves want to learnexactly how dripping water could form such amazing stoneshapes. But how did the caves form in the first place?

Water in Caves



Some caves form when waterflows underground. Water mightdrip from the ceiling, hang in theair, and form pools and streams.

Some caves form through weathering and erosion atEarth's surface. Wind and water may carve a cave from theside of a cliff. This kind of cave might be home to animalssuch as bears.

Other kinds of caves form when water flows underground.It moves through spaces in the soil and down throughcracks in solid rock. If this rock is limestone, water mixeswith and carries away the rock. Minerals that make up thelimestone are completely mixed in with the water thatmoves over it. The rooms and passages of a limestonecave form as water mixes with the rock and carries it away.

As water continues to drip into the open cave spaces, itcarries more minerals with it. The water deposits mineralson the floor or ceiling of the cave. Drip by drip, theseminerals build up for thousands of years. This dripping and



depositing creates all the different and amazing stoneshapes that you find in a cave.

If you ever visit a limestone cave, you will probably feel lotsof moisture in the air. You will usually hear water dripping.This means the cave is still forming. As long as there iswater in a cave, it will keep shaping the cave and its rockformations. A cave that is still growing and changing iscalled an active cave. In active caves, water can also formcave ponds and streams.

Cave Cones

A stalactite and a stalagmite cangrow so long that they might meetin the middle of the cave.

If you want to experience what a cave is like, go to a roomand turn off the lights! Without human-made light, a cave iscompletely dark. You cannot see anything. But with lights,beautiful formations may be revealed.

You might see cones hanging down toward the floor.



Stalactites are long cave formations that grow down fromthe ceiling. Stalactites look like icicles. Water seeping intoa limestone cave drips from the ceiling. The water leavesminerals that form thin, hollow tubes. These stalactites looklike soda straws, which is what they are called. Over time,water can flow along the outer edge of the soda straw,depositing more minerals. These minerals eventually makethe icicle shape.

In a cave, you might also see cones reaching up to thecave top. These are called stalagmites. They are formedbecause water dripping from the ceiling of a cave candeposit minerals on the floor. Stalagmites are often founddirectly beneath a stalactite. Stalagmites can be wide ornarrow, tall or short. A stalactite and a stalagmite can growso long that they meet. When they do, they become onevery large structure called a column.

Cave Textures

If you visit a cave, you should not touch any of its surfaces.Some formations can break very easily. So, even justtouching others can damage them. This is because the oilsin your skin can change the minerals. To satisfy curiousvisitors and still keep caves safe, guides often havesamples that visitors are allowed to feel. If you could toucha cave, you would feel many different textures.



Pieces of rock that fall off the walls and ceiling feel veryrough. So do the eroded surfaces of limestone. Anothercave formation occurs where water splashes and leavesbehind minerals. It is called cave popcorn. Just like thefood, cave popcorn has a very bumpy and rough surface.

Other surfaces in a limestone cave are very smooth. Flowstone looks likes a liquid and is often described as a frozenwaterfall. Other surfaces called “curtains” look like soft,folded fabric. Curtains with brown and tan stripes arecalled “cave bacon.”

With ceilings hung with bacon and floors covered inpopcorn, it is a wonder tour guides can keep visitors fromtasting cave formations! Of course, if they did, all theywould get is a mouthful of rocks.



A cave can have smooth and rough textures. “Cave bacon” curtains hang fromthe ceiling of this cave.

Yosemite Rock FormationsThis reading includes anonline resource. Login toyour subscription to viewit.

The sun rises over the valley at Yosemite National Parkand reveals massive gray rocks. These are CathedralRocks. The tall, pointed granite formations rise 2500 feetabove the Yosemite Valley. Cathedral Rocks are one of



the many rock formations that Yosemite is known for.Some people visit Yosemite to take in the beauty of thesegiant rocks. Others bring gear and are ready to climb to thetop. Imagine being able to see or climb a rock that is morethan 50 million years old!

So, when and how did these rocks form? They werecarved by glaciers a few million years ago. But the historyof the rock goes much further back. Most of Yosemite rockis a kind of rock called granite. About 65 million years ago,granite began to form when liquid rock inside Earth pushedits way to the surface and hardened. Then about 25 millionyears ago, the Sierra Nevada mountains and valleysbegan to slowly develop.

One million years ago, glaciers covered much of Yosemite.Ice covered the land for about 300,000 years. During thisperiod, moving glaciers shaped the landscape. The glacierthat carved Yosemite Valley created a flat-bottomed valley1 mile wide and 7 miles long. Cathedral Rocks were someof the many rock formations created as part of the 3,000-foot deep valley.



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