Erosion and Soil Erosion and Soil DepostionDepostion

Chapter 8Chapter 8

Section One:Section One:Changing Earth’s SurfaceChanging Earth’s Surface

ErosionErosion

““Erosion”Erosion” moves moves sediment from one sediment from one place to anotherplace to another

While While “deposition”“deposition” lays down lays down sediment in new sediment in new locations.locations.

What are the What are the forces which forces which

cause erosion?cause erosion?

The force of The force of gravity.gravity.

The force of The force of running water.running water.

The force of The force of glaciersglaciers..

The force of The force of waves.waves.

And the force of And the force of wind.wind.

What Do You Remember? What Do You Remember?

What does erosion do?What does erosion do? moves sediment from one place to moves sediment from one place to

anotheranother What does deposition do?What does deposition do? lays down sediment in new locations.lays down sediment in new locations. What are the forces which cause What are the forces which cause

erosion?erosion? Gravity, water, glaciers, waves, and Gravity, water, glaciers, waves, and

wind.wind.

Section 2: Water ErosionSection 2: Water Erosion

Moving water is Moving water is the major cause of the major cause of erosion on Earth’s erosion on Earth’s surface.surface.

Runoff and Erosion Runoff and Erosion

Runoff Runoff is is water which water which moves over moves over the land, the land, carrying soil carrying soil particles particles with it.with it.

The amount of The amount of erosion caused by erosion caused by runoff can depend runoff can depend on how much plant on how much plant life is there to hold life is there to hold the soil. With very the soil. With very little plant life, a little plant life, a desert can have desert can have high runoff and high runoff and erosion.erosion.

Because Because of gravity, of gravity, runoff and runoff and the soil in the soil in it carve it carve little little grooves grooves called called rillsrills..

As rills As rills flow into flow into one one another, another, they they grow grow larger larger and form and form gulliesgullies..

Gullies join Gullies join together to together to form form streamsstreams. . While While gullies only gullies only flow when it flow when it rains, rains, streams streams flow all the flow all the time.time.

A stream A stream grows into grows into a larger a larger stream by stream by receiving receiving water from water from tributariestributaries..

Together, all these Together, all these streams, from tiny rills to streams, from tiny rills to

great rivers, form a system great rivers, form a system that drains the land. A that drains the land. A

drainage basindrainage basin is a land is a land area where all this water area where all this water

collects.collects.

What Do You Remember?What Do You Remember?

What is the major cause of erosion on Earth’s What is the major cause of erosion on Earth’s surface?surface?

Moving water.Moving water. What is water which moves over the land, What is water which moves over the land,

carrying soil particles with it?carrying soil particles with it? RunoffRunoff Describe the system by which water is moved Describe the system by which water is moved

from small to large.from small to large. Rills to Gullies to Streams which are Rills to Gullies to Streams which are

Tributaries to Larger Streams, which run to a Tributaries to Larger Streams, which run to a Drainage Basin.Drainage Basin.

Rivers have features which Rivers have features which are caused by erosion.are caused by erosion.

Near its source, Near its source, a river flows a river flows quickly and quickly and follows a follows a straight, straight, narrow course. narrow course. The steep The steep slopes along the slopes along the river erode river erode rapidly and we rapidly and we see a deep, see a deep,

V-shaped valley V-shaped valley

WaterfallsWaterfalls occur occur where a river meets where a river meets an area of rock that an area of rock that is very hard, is very hard, followed by softer followed by softer rock. The soft rock rock. The soft rock wears away more wears away more quickly, creating a quickly, creating a waterfall.waterfall.

Lower down on Lower down on its course, a its course, a river usually river usually flows over more flows over more gently sloping gently sloping land. It spreads land. It spreads out and erodes out and erodes the land, the land, forming a forming a wide wide river valley.river valley.

A wide, A wide, flat area of flat area of land along land along a river is a river is called a called a flood flood plainplain. A . A river can river can cover the cover the flood plain flood plain during during floods.floods.

A river can A river can have have meandersmeanders, , which are which are looplike looplike bends in the bends in the river caused river caused by uneven by uneven erosion. erosion.

Sometimes a Sometimes a meandering meandering river forms an river forms an oxbow lakeoxbow lake. . This is a This is a meander that meander that has been cut has been cut off from the off from the river when river when the water the water level drops.level drops.

Complete River SystemComplete River System

What Features Do You What Features Do You Remember?Remember?

High in the mountains near the river’s source High in the mountains near the river’s source are…are…

deep, V-shaped valleys.deep, V-shaped valleys. When the river runs over hard rock, then soft When the river runs over hard rock, then soft

rock?rock? WaterfallsWaterfalls When it flows over gently sloping land?When it flows over gently sloping land? Wide river valleysWide river valleys When it comes to a wide, flat area of land?When it comes to a wide, flat area of land? Flood plainsFlood plains Looplike bends in the river caused by uneven Looplike bends in the river caused by uneven

erosion?erosion? MeandersMeanders

River DepositsRiver Deposits

As water As water moves, it moves, it carries carries sediments with sediments with it. Any time it. Any time moving water moving water slows down, it slows down, it drops some of drops some of the sediment.the sediment.

Soil deposition Soil deposition creates new creates new landforms, such landforms, such as as alluvial fansalluvial fans, , which is a wide, which is a wide, sloping deposit sloping deposit of sediment.of sediment.

Sediment Sediment deposited where deposited where a river flows a river flows into an ocean or into an ocean or lake builds up a lake builds up a landform called landform called a a deltadelta, which , which can take a can take a variety of variety of shapes, like this shapes, like this “birds foot” “birds foot” delta.delta.

What Do You Remember?What Do You Remember?

What happens when water flow slows What happens when water flow slows down?down?

The water drops its sediment.The water drops its sediment. What are wide, sloping deposits of What are wide, sloping deposits of

sediment?sediment? Alluvial fansAlluvial fans When a river flows into an ocean or lake, When a river flows into an ocean or lake,

sediment builds up at the mouth. What is sediment builds up at the mouth. What is this landform called?this landform called?

A deltaA delta

Groundwater Erosion and Groundwater Erosion and DepositionDeposition

Not all rainwater Not all rainwater goes to runoff or goes to runoff or evaporates. Some evaporates. Some of it soaks into the of it soaks into the ground. This ground. This underground water underground water is called is called groundwatergroundwater..

Underground water combines with Underground water combines with carbon dioxide to form a weak acid, carbon dioxide to form a weak acid, which can dissolve limestone. These which can dissolve limestone. These

hollowed out pockets in the hollowed out pockets in the underground stone become underground stone become cavescaves..

Inside the caves, Inside the caves, water containing water containing dissolved dissolved limestone drips limestone drips from the roof, from the roof, forming forming stalactitesstalactites (which (which hang down) and hang down) and stalagmitesstalagmites (which grow up (which grow up from the cave from the cave floor).floor).

Sometimes Sometimes the ground the ground above a above a cave can cave can collapse, collapse, creating a creating a depression depression called a called a sinkholesinkhole..

What Do You Remember?What Do You Remember? What is water that soaks into the ground?What is water that soaks into the ground? GroundwaterGroundwater How do caves form?How do caves form? Water combines with carbon dioxide to Water combines with carbon dioxide to

form a weak acid, which dissolves form a weak acid, which dissolves limestone.limestone.

What are the deposits of dissolved What are the deposits of dissolved limestone in caves called?limestone in caves called?

Stalactites (ceiling) and Stalagmites (floor).Stalactites (ceiling) and Stalagmites (floor). What is the name for a collapsed cave?What is the name for a collapsed cave? SinkholeSinkhole

Section 3: The Force of Section 3: The Force of Moving WaterMoving Water

A river’s A river’s moving moving water has water has energy, and energy, and we can use we can use this energy this energy to create to create power.power.

There are two There are two kinds of energy: kinds of energy: PotentialPotential Energy Energy

and and KineticKinetic Energy. Energy.

..

As water moves As water moves down from a down from a higher slope, its higher slope, its potential energy is potential energy is released into released into kinetic energy.kinetic energy.

This released This released energy picks energy picks up sediment, up sediment, pebbles, and pebbles, and even rocks, even rocks, which wear which wear the riverbed the riverbed away with a away with a grinding grinding action. This is action. This is called called abrasionabrasion..

The power The power of a river of a river depends on depends on how steep it how steep it is (is (slopeslope), ), how much how much water is water is flowing flowing ((volumevolume) ) and the and the shapeshape of its of its streambed.streambed.

A streambed can be full of boulders and A streambed can be full of boulders and other obstacles. All these rough other obstacles. All these rough

surfaces can increase friction, which surfaces can increase friction, which causes the water to move every which causes the water to move every which

way. This is called way. This is called turbulenceturbulence..

What Do You Remember?What Do You Remember? What are the two kinds of energy?What are the two kinds of energy? Potential and KineticPotential and Kinetic Water at a high place has which kind of energy?Water at a high place has which kind of energy? PotentialPotential Water flowing downhill has which kind of energy?Water flowing downhill has which kind of energy? KineticKinetic Moving water can be used to create…Moving water can be used to create… PowerPower The grinding action of pebbles and rocks on the riverbed is The grinding action of pebbles and rocks on the riverbed is

called…called… AbrasionAbrasion What are the three features which determine the power of a What are the three features which determine the power of a

river?river? Slope, volume, and shapeSlope, volume, and shape River obstcles like boulders create more friction, which River obstcles like boulders create more friction, which

increases…increases… TurbulenceTurbulence

Section 4: GlaciersSection 4: Glaciers

A A glacier glacier is any is any large large mass of mass of ice that ice that moves moves slowly slowly over over land.land.

There are two kinds of There are two kinds of glaciers: glaciers:

Valley Valley GlaciersGlaciers, , which are which are long, narrow long, narrow glaciers glaciers which forms which forms when snow when snow and ice build and ice build up high in a up high in a mountain mountain valley.valley.

Continental Continental GlaciersGlaciers, , which cover which cover much of a much of a continent continent or large or large island. They island. They cover 10% cover 10% of the earth of the earth today.today.

Many times in the past, Many times in the past, continental glaciers have covered continental glaciers have covered

large parts of Earth’s surface. large parts of Earth’s surface. These times are known as the These times are known as the ice ice

agesages..

Although glaciers Although glaciers move slowly, they move slowly, they are a major force are a major force of erosion.of erosion.

The glacier flows The glacier flows over the land and over the land and picks up rocks. This picks up rocks. This is called is called “plucking”.“plucking”. As the rocks are As the rocks are dragged across the dragged across the land they gouge land they gouge and scrape the and scrape the bedrock. This is bedrock. This is called called “abrasion”.“abrasion”.

When the glacier melts, it deposits the When the glacier melts, it deposits the sediments, which are called sediments, which are called “till”.“till”. The The

till at the edge of a glacier forms a till at the edge of a glacier forms a ridge, which is called a ridge, which is called a “moraine”“moraine” A A

“terminal moraine”“terminal moraine” is the farthest point is the farthest point reached by a glacier.reached by a glacier.

ContinentContinental glaciers al glaciers can scoop can scoop out huge out huge basins. basins. The Great The Great Lakes Lakes were were formed by formed by glaciers of glaciers of the past.the past.

What Do You Remember?What Do You Remember? What is a glacier?What is a glacier? A large mass of ice which moves over the land.A large mass of ice which moves over the land. What are the two kinds of glaciers?What are the two kinds of glaciers? Valley glaciers and Continental glaciers.Valley glaciers and Continental glaciers. What is an ice age?What is an ice age? A time when glaciers covered huge amounts of Earth.A time when glaciers covered huge amounts of Earth. What are the two things glaciers do to change the surface What are the two things glaciers do to change the surface

of earth?of earth? Plucking and AbrasionPlucking and Abrasion What are sediments left by glaciers called?What are sediments left by glaciers called? TillTill What is the ridge of sediment at the edge of a glacier?What is the ridge of sediment at the edge of a glacier? MoraineMoraine What is the farthest point of sediment left by a retreating What is the farthest point of sediment left by a retreating

glacier?glacier? Terminal Moraine.Terminal Moraine.

Section 5: WavesSection 5: Waves

The energy in waves comes from The energy in waves comes from wind that blows across the water’s wind that blows across the water’s

surface.surface.

The energy from The energy from waves can break waves can break apart rocks. Over apart rocks. Over time, waves can time, waves can make the small make the small cracks in the rocks cracks in the rocks larger. Eventually, larger. Eventually, pieces of the rock pieces of the rock break off.break off.

Waves also erode land by abrasion. When a Waves also erode land by abrasion. When a wave hits land, the sediment in it is carried wave hits land, the sediment in it is carried

forward by the wave and wears away rock like forward by the wave and wears away rock like sandpaper wearing away wood.sandpaper wearing away wood.

Waves not only erode the Waves not only erode the land, but they also deposit land, but they also deposit

sediment.sediment.

As waves reach the shore, As waves reach the shore, they drop the sediment they they drop the sediment they

carry, forming a beachcarry, forming a beach ..

What Do You Remember?What Do You Remember? What causes waves?What causes waves? The pressure of wind across the surface of The pressure of wind across the surface of

water.water. What causes waves to break on the beach?What causes waves to break on the beach? The friction of the land slows down the bottom The friction of the land slows down the bottom

water, but the top water keeps moving water, but the top water keeps moving forward.forward.

What are the two ways that waves erode land?What are the two ways that waves erode land? They hit rocks and cause cracks, and they They hit rocks and cause cracks, and they

abrade the rocks with their sediment like abrade the rocks with their sediment like sandpaper.sandpaper.

What deposits do waves leave?What deposits do waves leave? Sandy beaches.Sandy beaches.

Section 6: WindSection 6: Wind

Wind is actually the Wind is actually the weakest force of weakest force of erosion. Water, ice, erosion. Water, ice, and waves are much and waves are much stronger agents. But stronger agents. But wind can be a wind can be a powerful shaping powerful shaping force if there are no force if there are no plants to hold the plants to hold the soil in place.soil in place.

Wind picks up Wind picks up the smallest the smallest particles of particles of sediment. The sediment. The stronger the stronger the wind, the larger wind, the larger the particles it the particles it can pick up. This can pick up. This sweeping away sweeping away of earth is called of earth is called “deflation”.“deflation”.

When the When the wind slows wind slows down, or down, or some obstacle some obstacle traps the traps the windblown windblown material, material, sand dunessand dunes form. These form. These are formed by are formed by the coarser the coarser particles particles blown by the blown by the wind.wind.

The finer particles in the wind are carried very The finer particles in the wind are carried very far away from their source. These are particles far away from their source. These are particles of clay and silt and can create rich farmland. of clay and silt and can create rich farmland.

This windblown material is called This windblown material is called “loess”.“loess”.

What Do You Remember?What Do You Remember? When can wind be a powerful force for shaping When can wind be a powerful force for shaping

earth?earth? When there are few or no plants to hold the soil.When there are few or no plants to hold the soil. What is the sweeping away of particles by wind?What is the sweeping away of particles by wind? DeflationDeflation How are sand dunes formed?How are sand dunes formed? The wind-carried particles are trapped by The wind-carried particles are trapped by

obstacles or the wind slows down and drops the obstacles or the wind slows down and drops the particles.particles.

What are the finer particles which can be carried What are the finer particles which can be carried long distances before they fall?long distances before they fall?

LoessLoess