Chapter: Weathering and Erosion - PowerPoint PPT Presentation

About This Presentation
Title:

Chapter: Weathering and Erosion

Description:

Title: Slide 1 Author: Cherie Hatton Last modified by: cindah Created Date: 1/14/2004 3:26:19 PM Document presentation format: On-screen Show Company – PowerPoint PPT presentation

Number of Views:110
Avg rating:3.0/5.0
Slides: 67
Provided by: Cheri195
Category:

less

Transcript and Presenter's Notes

Title: Chapter: Weathering and Erosion


1
(No Transcript)
2
Table of Contents
Chapter Weathering and Erosion
Section 1 Weathering and Soil
Formation
Section 2 Erosion of Earths Surface
3
Weathering and Soil Formation
1
Weathering
  • Weathering is a mechanical or chemical surface
    process that breaks rocks into smaller pieces.
  • Freezing and thawing, oxygen in the air, and even
    plants and animals can affect the stability of
    rock.

4
Weathering and Soil Formation
1
Mechanical Weathering
  • Mechanical weathering breaks rocks into smaller
    pieces without changing them chemically.
  • The small pieces are identical in composition to
    the original rock.
  • Two of the many causes of mechanical weathering
    are ice wedging and living organisms.

5
Weathering and Soil Formation
1
Ice Wedging
  • Water seeps into cracks.
  • The deeper the cracks are, the deeper water can
    seep in.

6
Weathering and Soil Formation
1
Ice Wedging
  • The water freezes and expands, forcing the cracks
    to open further.

7
Weathering and Soil Formation
1
Ice Wedging
  • The ice melts.
  • If the temperature falls below freezing again,
    the process will repeat itself.

8
Weathering and Soil Formation
1
Plants and Animals
  • Plant roots grow deep into cracks in rock where
    water collects.
  • As they grow, roots become thicker and longer,
    slowly exerting pressure and wedging rock apart.

9
Weathering and Soil Formation
1
Plants and Animals
  • Gophers and prairie dogs also weather rockas do
    other animals that burrow in the ground.
  • As they burrow through sediment or soft
    sedimentary rock, animals break rock apart.

10
Weathering and Soil Formation
1
Chemical Weathering
  • Chemical weathering occurs when the chemical
    composition of rock changes.
  • This kind of weathering is rapid in tropical
    regions where it's moist and warm most of the
    time.

11
Weathering and Soil Formation
1
Chemical Weathering
  • The table summarizes the rates of chemical
    weathering for different climates.

12
Weathering and Soil Formation
1
Natural Acids
  • Some rocks react chemically with natural acids in
    the environment.
  • When water mixes with carbon dioxide in air or
    soil, for example, carbonic acids forms.

13
Weathering and Soil Formation
1
Natural Acids
  • Although carbonic acid is weak, it reacts
    chemically with many rocks.
  • When carbonic acid comes in contact with rocks
    like limestone, dolomite, and marble, they
    dissolve.

14
Weathering and Soil Formation
1
Plant Acids
  • Many plants produce a substance called tannin.
  • In solution, tannin forms tannic acid.
  • This acid dissolves some minerals in rocks.
  • Moss growing on rocks can cause chemical
    weathering.

15
Weathering and Soil Formation
1
Effect of Oxygen
  • Oxidation is the effect of chemical changes
    caused by oxygen.
  • When iron-containing materials such as steel are
    oxidized, a chemical reaction causes the material
    to rust.

16
Weathering and Soil Formation
1
Effect of Oxygen
  • When some iron-containing minerals are exposed to
    oxygen, they can weather to minerals that are
    like rust.
  • This leaves the rock weakened, and it can break
    apart.

17
Weathering and Soil Formation
1
Soil
  • Soil is a mixture of weathered rock, organic
    matter, water, and air that supports the growth
    plant life.
  • Organic matter includes decomposed leaves, twigs,
    roots, and other material.

18
Weathering and Soil Formation
1
Parent Rock
  • One factor affecting soil formation is the kind
    of parent rock that is being weather.
  • For example, in areas where sandstone is
    weathered, sandy soil forms.

Click image to view movie.
19
Weathering and Soil Formation
1
The Slope of the Land
  • The topography, or surface features, of an area
    also influence the types of soil that develop.
  • On steep hillsides, soil has little chance of
    developing.
  • This is because rock fragments move downhill
    constantly.

20
Weathering and Soil Formation
1
Climate
  • Climate affects the amount of organic material in
    soil.
  • Soils in desert climates contain little organic
    material.
  • However, in warm, humid climates, vegetation is
    lush and much organic material is present.

21
Weathering and Soil Formation
1
Climate
  • The result is the formation of a dark-colored
    material called humus.
  • Most of the organic matter in soil is humus.
  • Humus helps soil hold water and provides
    nutrients that plants need to grow.

22
Weathering and Soil Formation
1
Time
  • It can take thousands of years for some soil to
    form.
  • As soils develop, they become less like the rock
    from which they formed.
  • Thicker, well-developed soils often are found in
    areas where weathering has gone on undisturbed
    for a long period of time.

23
Weathering and Soil Formation
1
Organisms
  • Organisms influence soil development.
  • Lichens can grow directly on rock.
  • As they grow, they take nutrients from the rock
    that they are starting to break down, forming a
    thin soil.

24
Weathering and Soil Formation
1
Organisms
  • After a soil has formed, many types of plants
    such as grasses and trees can grow.
  • The roots of these plants further break down the
    parent rock.

25
Weathering and Soil Formation
1
Organisms
  • Dead plant material such as leaves accumulates
    and adds organic matter to the soil.

26
Section Check
1
Question 1
Explain how a tree can break apart rock.
Answer
As the tree grows, its roots become thicker and
longer. The roots exert pressure on the rocks
eventually breaking them apart.
27
Section Check
1
Question 2
How is a rusty nail an example of chemical
weathering?
Answer
When iron-containing materials, such as a nail,
are exposed to oxygen, a chemical reaction occurs
and rust is produced. The rust has a different
chemical composition than the nail.
28
Section Check
1
Question 3
Which of the following does NOT affect soil
formation?
A. climate B. carbonic acid C. organisms D.
topography
29
Section Check
1
Answer
The answer is B. Many factors affect
soil formation. Carbonic acid is responsible
for changing the chemical composition of
minerals in rock.
30
Erosion of Earths Surface
2
Agents of Erosion
  • Erosion is the wearing away and removal of rock
    or sediment.
  • Erosion occurs because gravity, ice, wind, and
    water sculpt Earth's surface.

31
Erosion of Earths Surface
2
Gravity
  • Gravity pulls everything on Earth toward its
    center.
  • When gravity alone causes rock or sediment to
    move down a slope, the erosion is called mass
    movement.
  • Mass movements can occur anywhere there are hills
    or mountains.

32
Erosion of Earths Surface
2
Creep
  • The process in which sediments move slowly
    downhill, is called creep.
  • Creep is common where freezing and thawing occur.

33
Erosion of Earths Surface
2
Creep
  • When soil freezes, particles are lifted.
  • When it thaws, the particles are pulled downhill
    by gravity.
  • Eventually, large amounts of sediment are moved
    by this process.

34
Erosion of Earths Surface
2
Slump
  • A slump occurs when a mass of rock or sediment
    moves downhill, leaving a curved scar.
  • Slumps frequently occur on slopes that have been
    undercut by erosion, such as those above the
    bases of cliffs that have been eroded by waves.

35
Erosion of Earths Surface
2
Rock Slides
  • During a rock slide layers of rock break loose
    from slopes and slide to the bottom.
  • The rock layers often bounce and break apart
    during movement.
  • This produces a huge, jumbled pile of rocks at
    the bottom of the slope.

36
Erosion of Earths Surface
2
Mudflows
  • A mudflow is a mass of wet sediment that flows
    downhill over the ground surface.
  • Some mudflows can be thick and flow slowly
    downhill at rates of a few meters per day.

37
Erosion of Earths Surface
2
Mudflows
  • Other mudflows can be much more fluid and move
    down slope at speeds approaching 160km/h.

38
Erosion of Earths Surface
2
Ice
  • When the ice in a glacier becomes thick enough,
    its own weight causes it to flow downhill under
    the influence of gravity.
  • A glaciers move over Earth's surface, they erode
    materials from some areas and deposit sediment in
    other areas.

39
Erosion of Earths Surface
2
Ice
  • Continental glaciers in polar regions cover about
    ten percent of Earth.
  • These glaciers are so large and thick that they
    can bury mountain ranges.

40
Erosion of Earths Surface
2
Ice
  • Valley glaciers are much smaller and are located
    in high mountains where the average temperature
    isn't warm enough to melt the ice sheets.

41
Erosion of Earths Surface
2
Glacial Erosion
  • Glaciers can erode rock in two different ways.
  • Ice can pull out pieces of rock.
  • This causes the rock to erode slowly. Loose
    pieces of rock freeze into the bottom of the
    glacier and are dragged along as the glacier
    moves.

42
Erosion of Earths Surface
2
Glacial Erosion
  • This scratching is the second way that glaciers
    can erode rock.
  • Scratching produces large grooves or smaller
    striations in the rock underneath.

Click image to view movie.
43
Erosion of Earths Surface
2
Effects of Glacial Erosion
  • In mountains, valley glaciers can remove rock
    from the mountaintops to form large bowls, called
    cirques (SURKS), and steep peaks.
  • When a glacier moves into a stream valley, it
    erodes rock along the valley sides, producing a
    wider, U-shaped valley.

44
Erosion of Earths Surface
2
Glacial Deposition
  • When stagnant glacier ice melts or when ice melts
    at the bottom of a flowing glacier or along its
    edges, the sediment the ice was carrying gets
    left behind on Earth's surface.
  • This sediment, deposited directly from glacier
    ice, is called till.

45
Erosion of Earths Surface
2
Glacial Deposition
  • A lot of melting occurs around glaciers.
  • So much water can be produced that streams often
    flow away from the glacier.
  • These steams carry and deposit sediment.
  • Sand and gravel deposits laid down by these
    streams are called outwash.

46
Erosion of Earths Surface
2
Wind
  • When wind blows across loose sediments like silt
    and sand, it lifts and carries it.
  • Wind often leaves behind particles too heavy to
    move.
  • This erosion of the land by wind is called
    deflation.

47
Erosion of Earths Surface
2
Wind
  • Abrasion is a form of erosion that can make pits
    in rocks and produce smooth, polished surfaces.
  • Abrasion is common in some deserts and in some
    cold regions with strong winds.

48
Erosion of Earths Surface
2
Wind
  • If sand deposit continues to grow, a sand dune
    might form.
  • Sand dunes move when wind carries sand up one
    side of the dune and it avalanches down the other.

49
Erosion of Earths Surface
2
Wind
  • Sometimes, wind carries only fine sediment called
    silt.
  • When this sediment is deposited, an accumulation
    of silt called loess (LOOS) can blanket Earth's
    surface.
  • Loess often is deposited downwind of large
    deserts and deflated glacial outwash deposits.

50
Erosion of Earths Surface
2
Water
  • Water that flows over Earth's surface is called
    runoff.
  • Runoff is an important agent of erosion.
  • The more speed water has, the more material it
    can carry with it.

51
Erosion of Earths Surface
2
Sheet Flow
  • When water flows downhill as a thin sheet, it is
    called sheet flow.
  • This thin sheet of water can carry loose sediment
    grains with it, causing erosion of the land.
  • This erosion is called sheet erosion.

52
Erosion of Earths Surface
2
Rills and Gullies
  • Where a sheet of water flows around obstacles and
    becomes deeper, rills can form.
  • Rills are small channels cut into the sediment at
    Earth's surface.
  • These channels carry more sediment than can be
    moved by sheet flow.

53
Erosion of Earths Surface
2
Rills and Gullies
  • As runoff continues to flow through the rills,
    more sediment erodes and the channel widens and
    deepens.
  • When the channels get to be about 0.5m across,
    they are called gullies.

54
Erosion of Earths Surface
2
Streams
  • Gullies often connect to stream channels.
  • Most streams have water flowing through them
    continually, but some have water only during part
    of the year.

55
Erosion of Earths Surface
2
Streams
  • In mountainous and hilly regions, streams flow
    down steep slopes.
  • This type of stream typically has white-water
    rapids and may have water falls.

56
Erosion of Earths Surface
2
Streams
  • As streams move out of the mountains and onto
    flatter land, they begin to flow more smoothly.
  • The streams might snake back and forth across
    their valley, eroding and depositing sediments
    along their sides.

Click image to view movie.
57
Erosion of Earths Surface
2
Shaping Earths Surface
  • Over long periods of time, water moving in a
    stream can have enough power to cut large canyons
    into solid rock.
  • Many streams together can sculpt the land over a
    wide region, forming valleys and leaving some
    rock as hills.

58
Erosion of Earths Surface
2
Shaping Earths Surface
  • When rivers enter oceans or lakes, the water
    slows and sediment is deposited.
  • This can form large accumulations of sediment
    called deltas.

59
Section Check
2
Question 1
Compare and contrast continental glaciers and
valley glaciers.
60
Section Check
2
Answer
Continental glaciers are located in Polar Regions
and are very large and thick. Valley glaciers are
much smaller and are found high up in the
mountains where the average temperature is not
warm enough to melt the ice. Glaciers can erode
rock by pulling out pieces of rock underneath
them and dragging them along the surface as the
glacier moves.
61
Section Check
2
Question 2
Which is NOT caused by water erosion?
A. abrasion B. canyons C. gullies D. sheet erosion
62
Section Check
2
Answer
The correct answer is A. Abrasion results when
wind carrying sediment wears down other rocks.
63
Section Check
2
Question 3
Identify and describe the process being
illustrated by this diagram?
64
Section Check
2
Answer
The process shown is called creep. Creep occurs
when sediments slowly move downhill. It is common
in areas where freezing and thawing occur. As the
ice expands in the soil, sediments move up. When
the soil thaws, the sediments move further
downslope by gravity.
65
Help
To advance to the next item or next page click on
any of the following keys mouse, space bar,
enter, down or forward arrow.
Click on this icon to return to the table of
contents
Click on this icon to return to the previous slide
Click on this icon to move to the next slide
Click on this icon to open the resources file.
Click on this icon to go to the end of the
presentation.
66
End of Chapter Summary File
Write a Comment
User Comments (0)
About PowerShow.com