1. Chapter 9:1 Reading Check
__________, ___________, and __________ act together in a cycle that wears down and builds up Earth’s surface.
________, ___________, __________, _______, and ________ all cause erosion.
_______ causes mass movement, the process that moves sediment downhill.
The different types of mass movement include ________, _________, _______, and ________.
Mass movement can be ________ or ________.

2. 9:1 Answers Weathering, erosion, and deposition
Gravity, running water, glaciers, waves, and wind
Gravity
Landslides, mudflows, slump, and creep
Rapid or slow

3. Erosion and Deposition
Chapter 9

4. Changing Earth’s surface
Section 1

5. Changing Earth’s Surface
Erosion is the process by which natural forces move weathered rock and soil from one place to another
Gravity, running water, glaciers, waves, and wind all cause erosion
The material moved by erosion is sediment
When the agents of erosion lay down sediment, deposition occurs
Deposition changes the shape of the land
Weathering, erosion, and deposition act together in a cycle that wears down and builds up Earth’s surface
Erosion and deposition are at work everywhere on Earth
Erosion and deposition are never-ending

6. Gravity Gravity pulls everything toward the center of Earth
Gravity is the force that moves rock and other materials downhill
Gravity causes mass movement, any one of several processes that move sediment downhill
The different types of mass movement include landslides, mudflows, slump, and creep
Mass movement can be rapid or slow

7. Landslides
The most destructive type of mass movement is a landslide, which occurs when rock and soil slide quickly down a steep slope
Some landslides contain huge masses of rock, while others may contain only a small amount of rock and soil

8. Mudflow
A mudflow is the rapid downhill movement of a mixture of water, rock, and soil
The amount of water in a mudflow can be as high as 60 percent
Mudflows often occur after heavy rains in a normally dry area
In clay soils with a high water content, mudflows may occur even on very gentle slopes
An earthquake can trigger both mudflows and landslides

9. Slump
In the type of mass movement known as a slump, a mass of rock and soil suddenly slips down in one large mass
It looks as if someone pulled the bottom out from under part of the slope
A slump often occurs when water soaks the base of a mass of soil that is rich in clay

10. Creep Creep is the very slow downhill movement of rock and soil
It occurs most often on gentle slopes
Creep often results from the freezing and thawing of water in cracked layers of rock beneath the soil
Creep is so slow that you can barely notice it, but you can see its effects in objects such as telephone poles, gravestones, and fenceposts
Creep may tilt these objects at spooky angles

12. Chapter 9:2 reading check
What is the major agent of erosion that has shaped Earth’s land surface?
A river creates valleys, waterfalls, flood plains, meanders, and oxbow lakes through ____________.
Landforms such as alluvial fans and deltas are created by __________.
Groundwater can cause erosion through the process of _____________________.

13. Ch. 9:2 reading check answers
Moving water
Erosion
Deposition
Chemical weathering

14. Water Erosion
Chapter 9 section 2

15. Moving water
Moving water is the major agent of erosion that has shaped Earth’s land surface
The force of a falling raindrop can loosen and pick up soil particles
As water moves over land, it carries these particles with it
This moving water is called runoff, which is water that moves over Earth’s surface
The amount of runoff in an area depends on five main factors
Amount of rain, amount of vegetation, type of soil, shape of the land, and how people use the land

16. Runoff Travels
As runoff travels, it forms tiny grooves in the soil called rills
Rills flow into one another and form larger grooves, called gullies
A gully is a large groove, or channel, in the soil that carries runoff after a rainstorm
Gullies join together to form streams
A stream is a channel along which water is continually flowing down a slope
A tributary is a stream that flows into a larger stream

17. Erosion
Through erosion, a river creates valleys, waterfalls, flood plains, meanders, and oxbow lakes
Rivers often form on mountain slopes. There, a river generally follows a straight, narrow course, creating a deep, V-shaped valley. Lower down, a river usually flows over more gently sloping land
The river spreads out, forming a wide river valley
The flat, wide are of land along a river is a flood plain
A meander is a looplike bend in the course of a river
Sometimes a meandering river forms an oxbow lake
A meander that has been cut off from the river

18. Deposition As water moves, it carries sediment with it
Whenever moving water slows down, it deposits sediment. Deposition creates landforms such as alluvial fans and deltas. It can also add soil to a river’s flood plain
When a river flows out of a mountain valley, the water slows down
Then sediments are deposited in an alluvial fan, a wide, sloping deposit formed where a stream leaves a mountain range
A river ends when it flows into a still body of water, such as an ocean or a lake
There the water slows down and deposits sediment
This sediment builds up a landform called a delta
Deposition also occurs during floods

19. Groundwater
When rain falls, some water soaks into the ground, filling openings in soil and cracks in rocks.
This underground water is called groundwater
Groundwater can cause erosion through a process of chemical weathering
Over time, this weathering can develop into caves or caverns and also result in deposition
a deposit that hangs like an icicle from the roof of a cave is a stalactite
Slow dripping can build up a cone-shaped stalagmite on a cave floor
In rainy regions where a layer of limestone is near the surface, groundwater can change the shape of the land
Such a landscape is called karst topography

20. The Force of Moving Water
9:3

21. Energy A river’s water has energy
Energy is the ability to do work or cause change
Potential energy is energy that is stored and waiting to be used later
Kinetic energy is the energy an object has due to its motion
As gravity pulls water down a slope, the water’s potential energy changes to kinetic energy that can do work
All along a river, moving water causes changes
A river is always moving sediment from place to place
At the same time, a river is also eroding its banks and its valley

22. Sediment
In the process of water erosion, water picks up and moves sediment. Sediment can enter rivers in a number of ways.
Most sediment washes or falls into a river as a result of mass movement and runoff
Other sediment erodes from the bottom or sides of the river
Wind may also drop sediment into the water
Abrasion is another process by which a river obtains sediment
Abrasion is the wearing away of rock by a grinding action

23. Sediment The amount of sediment that a river carries is its load
Gravity and the force of moving water cause sediment to move downstream
A river’s slope, its volume of flow, and the shape of its streambed all affect how fast the river flows and how much sediment it can erode

24. A fast flowing river carries more and larger particles of sediment
When a river slows down, it deposits some of its sediment load
Generally, as a river’s slope increases, its speed also increases
A river’s slope is the amount the river drops toward sea level over a given distance
If a river’s speed increases, its sediment load and power to erode may increase
A river’s flow is the volume of water that moves past a point on the river at any given time
As more water flows through a river, its speed increases

25. Friction
Friction is the force that opposes the motion of one surface as it moves across another surface
Friction affects a river’s speed
Where a river is deep, less water comes in contact with the streambed
This reduces friction and allows the river to flow faster
In a shallow river, there is more friction, which reduces the river’s speed
A streambed is often full of boulders and other obstacles
This roughness increases friction and reduces a river’s speed
The water moves every which way in a type of movement called turbulence
Turbulence slows a stream’s flow, but a turbulent stream has great power to erode

26. Shape The shape of a river affects the way it deposits sediment
Deposition occurs along the sides of a river, where the water moves more slowly
If a river curves, the water moves fastest on the outside of the curve
There, the river erodes
On the inside of the curve, where the speed is slowest, the river deposits sediment

27. Glaciers
Section 4

28. Continental Glacier
A glacier is any large mass of ice that moves slowly over land
Continental glacier
Covers much of a continent or large island
Today, they cover about 10 percent of Earth’s land, including Antarctica and most of Greenland
Can flow in all directions

29. Ice Ages
Many times in the past, continental glaciers have covered large parts of Earth’s surface
These times are known as ice ages
For example, about 2.5 million years ago, continental glaciers covered about a third of Earth’s land
The glaciers advanced and retreated, or melted back, several times
They retreated for the last time about 10,000 years ago
A valley glacier is a long, narrow glacier that forms when snow and ice build up high in a mountain valley
Valley glaciers are found on high mountains

30. Snow Fall
Glaciers can form only in an area where more snow falls than melts
When the depth of snow and ice reaches more than 30 to 40 meters, gravity begins to pull the glacier downhill
Valley glaciers move, or flow, at a rate of a few centimeters to a few meters per day
Sometimes a valley glacier slides down more quickly in what is called a surge

31. Plucking and Abrasion
The movement of a glacier changes the land beneath it. Although glaciers work slowly, they are a major force of erosion.
The two processes by which glaciers erode the land are plucking and abrasion
As a glacier flows over the land, it picks up rocks in a process called plucking
Plucking can move even huge boulders
many rocks remain on the bottom of a glacier, and the glacier drags them across the land
This process, called abrasion, gouges and scratches the bedrock

32. Sediment
A glacier gathers huge amounts of rock and soil as it moves. When a glacier melts, it deposits the sediment it eroded from the land, creating various landforms
The mixture of sediments that a glacier deposits directly on the surface is called till
The till deposited at the edges of a glacier forms a ridge called a moraine
A terminal moraine is the ridge of till at the farthest point reached by a glacier
Retreating glaciers also create features called kettles
A kettle is a small depression that forms when a chunk of ice is left in glacial till
When the ice melts, the kettle remains
A kettle that is filled with water is called a kettle lake

33. Waves
Section 5

34. Energy Ocean waves contain energy
The energy in waves comes from wind that blows across the water’s surface
The energy that water picks up from the wind causes water particles to move up and down as the waves go by
The water particles themselves don’t move forward

35. Erosion Waves are a major force of erosion along coasts
Waves shape the coast through erosion by breaking down rock and transporting sand and other sediment
One way waves erode the land is by impact
Large waves can hit rocks along the shore with great force
This energy can break apart rocks
Waves also erode by abrasion
As a wave approaches shallow water, it picks up sediment, including sand and gravel
This sediment wears away rock like sandpaper wearing away wood

36. Waves coming to shore gradually change direction
The change in direction occurs as different parts of a wave begin to drag the bottom
The energy of these waves is concentrated in the headlands
A headland is a part of the shore that sticks out into the ocean
Over time, waves erode the headlands and even out the shoreline

37. Coasts
Waves shape a coast when they deposit sediment, forming coastal features such as beaches, spits, and barrier beaches
Deposition occurs when waves slow down, causing the water to drop its sediment
As waves reach the shore, they drop the sediment they carry, forming a beach

38. Beaches A beach is an area of wave-washed sediment along the coast
The sediment on a beach usually moves down the beach after it has been deposited
Waves usually hit the beach at an angle instead of straight on
These angled waves create a current that runs parallel to the coastline
As waves repeatedly hit the beach, some of the beach sediment moves down the beach with the current, in a process called longshore drift

39. Spit One result of longshore drift is the formation of a spit
A spit is a beach that projects like a finger out into the water
Spits occur where a headland or another obstacle interrupts longshore drift

40. Incoming waves
Incoming waves may build up sandbars, long ridges of sand parallel to shore
A barrier beach is similar to a sand bar
Barrier beaches are found in many places along the Atlantic coast of the United States

41. Wind
Section 6

42. Wind A sand dune is a deposit of wind-blown sand
Wind is the weakest agent of erosion
Yet wind can be a powerful force in shaping the land in areas where there are few plants to hold the soil in place
For example, in deserts, few plants grow, where wind can easily move the grains of dry, light sand

43. Wind Erosion Wind causes erosion by deflation and abrasion
Geologists define deflation as the process by which wind removes surface material
When wind blows over the land, it picks up particles of sediment
The stronger the wind, the larger the particles that it can pick up and move through the air
Particles that are too heavy to be picked up might skip or bounce for a short distance
Strong winds can even roll heavier sediment particles over the ground

44. Deflation does not usually have a great effect on the land
In deserts, though, deflation can sometimes create an area of rock fragments called desert pavement
There, wind has blown away smaller sediment
All that remains are rocky materials that are too heavy to be moved by wind
Abrasion by wind-carried sand can polish rock, but it causes little erosion
At one time, geologists thought such abrasion cut the stone shapes seen in deserts
But evidence now shows that most desert landforms are the result of weathering and water erosion

45. Deposition
All sediment picked up by wind eventually falls to the ground
This happens when wind slows down or some obstacle, such as a boulder or clump of grass, traps the windblown sand and other sediment
Wind erosion and deposition may form sand dunes and loess deposits

46. Sand Dunes
When wind carrying sand strikes an obstacle, the result is usually a sand dune
Sand dunes can be seen on beaches and in deserts where windblown sediment has built up
Sand dunes come in many shapes and sizes
Sand dunes move over time
Plant roots can help anchor a sand dune in place

47. Loess
Sediment that is finer than sand is sometimes deposited in layers far from its source
This fine, wind-deposited sediment is loess
Large loess deposits are found in central China and in such states as Nebraska, South Dakota, Iowa, Missouri, and Illinois
Loess helps form fertile soil