The Dynamic Earth

1
The Dynamic Earth
2
The Dynamic Earth

• Movement of the Earths crust (Ch 10)
• Earthquakes and volcanoes (Ch 11)
• Plate tectonics (Ch 12)
• Rocks and minerals (Ch 13)
• Weathering and soil formation (Ch 14)
• Erosion and deposition (Ch 15)

3
Erosion and Deposition

• Read pages 453-454

4
Erosion and Deposition

• Erosion
• The process by which weathered rock and soil
  particles are moved from one place to another
• Erosion can be caused by
• Gravity
• Wind
• Running water
• Glaciers
• Waves

5
Erosion and Deposition

• Deposition
• The process by which sediments are laid down in
  new locations

6
Section Review Questions

• Section 15-1
• What are the five agents of erosion?
• How does erosion change the Earths surface?
• What is deposition?
• How does deposition change the surface of the
  Earth?

7
Gravity

• Read pages 455-456

8
Erosion and Deposition

• Gravity pulls rocks and soil down slopes
• Called mass wasting
• Can occur rapidly or slowly
• Rapid
• Landslide a tumbling of soil, rocks, and
  boulders
• Mudflow usually occurs after a heavy rain
• Slump block of rock or soil on the face of a
  steep slope that slips down so its upper surface
  is tilted back
• Slow
• Earthflow occurs after a heavy rain
• Soil creep disturbance of soil particles by
  freezing, animal activity or water movement

9
Section Review Questions

• Section 15-2
• How does gravity cause erosion?
• What is rapid mass wasting? Give two examples.
• What is slow mass wasting? Give two examples.

10
Wind

• Read pages 456-459

11
Erosion and Deposition

• Wind
• Wind is the most active agent of erosion in
  deserts, in plowed fields, and on the beaches

12
Types of Wind Erosion

• Wind erodes the Earths surface in two ways
• Deflation
• Fine particles are carried many meters up into
  the air
• Abrasion
• When particles carried by the wind act like a
  sandblaster, cutting and polishing rocks

13
Deposits by Wind

• The amount of rock and soil particles carried by
  the wind depends on the speed of the wind
• As wind slows down, it cannot carry as many
  particles

14
Dunes

• The deposits of windblown sand which occurs near
  bushes or rocks
• As the dunes form, it slows the wind down and
  more sand is deposited
• Eventually it will become a sand dune
• This is a mound of sand deposited by the wind

15
Sand Dunes

• Vary in size and shape
• The side that faces the wind is a gentle slope
• The side away from the wind is a steep slope
• Sand dunes move by being eroded away on one side
  and deposited on the other

16
Loess

• The deposits of fine particles of sand and silt
  deposited many miles away
• These areas are very fertile
• These deposits are light in color and may be many
  meters thick.

17
Windbreak

• Is often used to decrease wind erosion and aid in
  wind deposition
• A barrier that causes the wind to slow down
• When wind speed is decreased, the load carried by
  the wind is dropped

18
Section Review Questions

• Section 15-3
• Where is wind the most active agent of erosion?
• How are deflation and abrasion different?
• What are two kinds of deposits caused by wind?

19
Running Water

• Read pages 460-465

20
Running Water

• Running water changes more of the Earths surface
  than any other agent of erosion
• Running water is the major cause of erosion
• Rivers, streams, and runoff are forms of running
  water

21
Runoff and Erosion

• When rain falls on the surface of the Earth,
  three things can happen to the water
• The rain can evaporate
• It can sink into the ground
• It can flow over the land surface as runoff

22
Runoff and Erosion

• When water moves across the Earths surface as
  runoff, it picks up and carries particles of
  clay, sand, and gravel
• This water and sediments move downhill as a
  result of gravity
• While these particles are moving, they continue
  to wear away the soil and form grooves, called
  rills

23
Runoff and Erosion

• Rills become wider and deeper and eventually form
  gullies
• Gullies act as channels for runoff

24
Runoff and Erosion

• The amount of runoff is affected by several
  factors
• The amount of rainfall
• In areas of high average rainfall, there is a lot
  of runoff, there is a lot of erosion
• The amount of plant growth in an area
• Plant roots hold soil particles in place and help
  to absorb some of the water
• Areas with little plant growth have greater
  runoff and therefore greater erosion

25
Runoff and Erosion

• The amount of runoff is affected by several
  factors
• The shape of the land
• Steep slopes have the greatest amount of runoff
• Water moves too fast to soak into the ground
• As the water moves rapidly down the hill, a lot
  of erosion takes place

26
Streams and Erosion

• When the water from several gullies comes
  together, a stream forms
• Streams carry large amounts of sediments
• The soil particles and rock materials carried
  along by the stream are called the streams load

27
Streams and Erosion

• Sediments are carried different ways
• Large, heavy sediments, such as pebbles and
  boulders, are pushed or rolled downstream
• Lighter sediments, such as silt or clay, are
  picked up and carried along by the force of the
  moving water
• There sediments, such as salts, dissolve in the
  water

28
Streams and Erosion

• Streams cause erosion by abrasion
• Sediments carried by streams constantly collide
  with rocks, chipping away pieces and wearing down
  the rocks
• Different types of rock layers will result in
  different types of abrasion

29
Development of a River System

• Runoff forms rills, rills deepen and widen into
  gullies, gullies form streams, streams join to
  form rivers
• Rivers usually begin in mountains and hills
• Rivers affect large areas by erosion

30
Development of a River System

• The network of rills, gullies, streams, and
  rivers in an area is called a drainage system
• A tributary is a main source of water for a river
• Many tributaries feed the river

31
Development of a River System

• The area drained by a main river and its channels
  is called a drainage basin
• The land that separates one drainage basin from
  another is called a divide
• One of the larges divides is called the
  Continental Divide
• This is a divide that passes down the center of
  the Rocky Mountains
• West of the divide, water goes to the Pacific
• East of the divide, water goes to the Atlantic

32
Development of a River System

• The divide may start off wide, but as the
  drainage system of a river develops, the divide
  becomes narrower

33
Life Cycle of a River

• An immature river, or a young river, is a river
  in an early stage of development
• Water flows very rapidly over the surface
• This is able to move large rocks and produce a
  lot of runoff

34
Life Cycle of a River

• A river that has been developing for many
  thousands of year is called a mature river
• Because of continuous erosion, the rapids and
  waterfalls have largely disappeared
• The river is curved and winding, forming loops
  called meanders
• The water has slowed down so erosion has slowed
  down

35
Deposits by Rivers

• A stream or river carries a large amount of
  sediments
• Deposits are left where a stream bends or curves
• The outside of the curve receives the full impact
  of the current

36
Oxbow Lakes

• This is a U-shaped lake that forms when a river
  meanders in a curve and eventually cuts off the
  ends forming a lake

37
Alluvial Fans

• When the sediments carried by a rapid moving
  river are dropped because the river slows down
• This deposit forms a fan-like shape

38
Deltas

• Large amounts of sediments deposited at the mouth
  of a large river that flows into a lake or an
  ocean form a delta
• Sediments can build up near the mouth of a river

39
Flood Plains and Levees

• Flood plains form when a river overflows and
  sediments are deposited in the area around the
  river
• Flood plains are very fertile
• The ridgelike deposits along the sides of the
  river are called levees

40
Section Review Questions

• Section 15-4
• What is the major cause of erosion?
• What factors affect the amount of runoff?
• What is a drainage system? A drainage basin?
• Compare an immature river to a mature river.
• How are deltas and flood plains formed?

41
Glaciers

• Read pages 466-470

42
Glaciers

• A large mass of moving ice and snow
• Review chapter 7

43
Glacial Ice and Erosion

• Glacial ice erodes by abrasion and by plucking
  away at the rock beneath it
• Rock materials carried by a glacier are called
  glacial debris
• Particles in the glacier scrapes along rocks and
  leaves scratches

44
Deposits by Glaciers

• As a glacier comes to warmer climates, it begins
  to melt and leave behind rocks and debris
• This debris is called till

45
Moraines

• When a glacier melts and retreats, it leaves
  behind till
• Till forms a ridge called a moraine
• Till at the front side of the glacier is called
  terminal moraine
• Till at the sides of the glacier is called a
  lateral moraine
• Scientists study tills to find where the glacier
  formed

46
Drumlins

• An oval-shaped mound of till
• Formed as deposits of till are rounded by glacial
  ice

47
Meltwater Deposits

• Meltwater forms when the glacier stops moving and
  begins to melt
• These rivers of melted water carry sediments and
  deposit them along a stream beds called valley
  trains
• These deposits form areas called outwash plains
• These plains are very fertile
• Many farms today can be found in these areas

48
Iceberg Deposits

• Icebergs may contain rocks and debris picked up
  from land
• As the iceberg melts, the rocks and debris are
  deposited on the ocean floor

49
Glacial Lakes

• Glaciers form many lakes including the Finger
  Lakes in New York, the Great Lakes and other
  smaller lakes

50
Glacial Lakes

• Glaciers can form lakes in two ways
• Glacial till piles up in low-lying river channels
  and other areas
• These deposits keep water from flowing away from
  land
• Ice blocks are surrounded or covered with
  sediments deposited by the glaciers
• When the ice melts, it leaves a depression, or
  hole, in the ground
• These lakes are known as kettle lakes

51
Section Review Questions

• Section 15-5
• How does a glacier erode the Earths surface?
• Compare a valley glacier and a continental
  glacier.
• What is till? A moraine? A drumlin?
• What are two meltwater deposits?
• How are glacial lakes formed?

52
Waves

• Read pages 470-474

53
Waves

• The powerful force of waves constantly erodes and
  shapes the shoreline

54
Waves and Erosion

• Waves cause erosion in several ways
• The force of waves hitting the rocks
• The particles in the waves rubbing against the
  rocks
• Forcing water up into cracks and making the
  cracks bigger
• Salt water dissolving some minerals

55
Waves and Erosion

• Erosion at a shoreline can occur at different
  rates
• The size and the force of the waves hitting the
  shoreline have an effect on the rate of erosion
• Certain rocks erode more quickly than others

56
Sea Cliffs and Terraces

• Steep faces of rock that are formed by wave
  erosion are called sea cliffs
• The flat place at the bottom of a sea cliff is
  called the terrace
• This area is made up of the ground up particles
  of the sea cliff

57
Sea Stacks and Caves

• The columns of resistant rock left behind from
  sea cliffs are called sea stacks
• A sea cave is a hollowed out portion of a sea
  cliff

58
Deposits by Waves

• Waves carry large amounts of sand, rock particles
  and pieces of shells
• Beaches
• Are made up of eroded rock particles deposited on
  the shoreline
• The color of beach sand depends on the source
  rock from which it came

59
Sand Bars and Spits

• When water currents turn and flow parallel to the
  shoreline it is called a longshore current
• If the shoreline bends or curves, materials
  carried by waves in a longshore current is
  deposited in open water and forms a sand bar
• If the sandbar is connected to the curving
  shoreline, it is called a spit

60
The Shape of the Shoreline

• The shape of the shoreline often results from
  changes in the level of the sea
• A drop in the ocean forms more sea cliffs
• A rise in the ocean forms more harbors and bays

61
Section Review Questions

• Section 15-6
• How do waves affect a shoreline?
• What is a sea cliff? A sea stack?
• Why do different beaches have different colored
  sand?
• How does a longshore current form sand bars and
  spits?

62
Chapter Review

• Pages 478-479
• Multiple Choice
• 1-10
• True or False
• 1-7
• Concept Mapping
• Extra Credit
• Concept Mastery
• Answer 5 of the 9 questions