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Volcanoes and Igneous Activity Earth - Chapter 4

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Chapter 5 Weathering, Soil, and Mass Movements * * * * Characteristics of Soil 5.2 Soil Soil Structure Soil particles clump together to give a soil its structure. – PowerPoint PPT presentation

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Title: Volcanoes and Igneous Activity Earth - Chapter 4


1
Chapter 5
Weathering, Soil, and Mass Movements
2
Weathering
  • Earth is continuously undergoing natural breaking
    down process Weathering

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4
  • Weathering
  • the breaking down of rocks and other materials on
    the Earths surface
  • A slow and continuous process
  • Affects all substances exposed to the atmosphere
  • The effects are not always easily observed due to
    how long weathering takes.

5
  • Two types of weathering
  • Mechanical
  • Chemical

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7
5.1 Weathering
? Mechanical weathering occurs when physical
forces break rock into smaller and smaller pieces
without changing the rocks mineral composition.
? In nature three physical process are especially
important causes of weathering frost wedging,
unloading, and biological activity.
8
NOTES
  • Mechanical Weathering
  • Forces of weathering break rocks into smaller
    pieces but do not change the chemical makeup of
    the rock.
  • Strictly a physical process
  • Common agents of Mechanical weathering are ice,
    plants, animals, gravity, running water and wind
  • Like hitting a rock with a hammer and smashing it
    to pieces.
  • At the beginning of weathering, rock fragments
    are usually angular and sharp. As weathering
    continues they become smooth and rounded.

9
Increase in Surface Area by Mechanical Weathering
10
NOTES
  • Causes of Mechanical Weathering
  • Temperature
  • Changes in temperature can cause rocks to break
    apart.
  • The outside of the rock is heated and expands
    while the inside of the rock remains cool and
    does not expand. When the temperature drops, the
    outside of the rock cools and contracts.
  • This cycle repeats every day and causes the
    particles to crack and flake off.
  • Exfoliation pieces break off in curved sheets
    or slabs parallel to rocks surface. Other
    agents also cause exfoliation.

11
5.1 Weathering
1. Frost wedging
  • The mechanical breakup of rock caused by the
    expansion of freezing water in cracks and crevices
  • Sections of rock that are wedged loose may tumble
    into large piles called talus, which typically
    form at the base of steep, rocky cliffs.

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13
Frost Wedging
14
NOTES
2. Frost Action or Ice Wedging
  • Water expands in volume by about 10 when it
    freezes Repeated freezing and melting of water
  • Water seeps into a small opening or crack in a
    rock, the temperature drops below freezing, the
    water freezes and expands.
  • The crack is made larger by the pressure of the
    water as it expands.
  • Over time the cycle causes the rock to break into
    pieces.
  • Talus large piles of broken rock.

15
NOTES
  • Cracks and potholes in roads and cement driveways
    are often caused by frost action.
  • Commonly occurs at high elevations and in
    climates where the temperature regularly varies
    above and below freezing Northern US.

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17
5.1 Weathering
2. Unloading
  • Reduced pressure on igneous rock causes it to
    expand and allows slabs of outer rock to break
    off in layers in a process called exfoliation.

3. Biological activity
  • The activity of organisms, including plants,
    burrowing animals, and humans, can also cause
    mechanical weathering.

18
Unloading and Exfoliation of Igneous Rocks
19
Weathering and Biological Activity
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4. Organic/Biological Activity
  • Root-pry - Roots of plants loosen rock material
    by growing in a crack in a rock and make the
    crack larger are the plants roots grow and
    spread out.
  • Digging of borrowing animals expose new rock
    surfaces to weathering.

22
5. Gravity
  • Landslides - Pull loosened rocks down mountain
    cliffs
  • Landslide large movement of loose rocks and
    soil As the rocks fall, they collide with one
    another and break into smaller pieces.
  • A type of abrasion

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Mine
NG Video
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26
Abrasion
  • The wearing away of rocks by solid particles
    carried by wind, water or other forces.
  • Sand Blasting - Sharp edges of sand particles
    scrape off small pieces of exposed rock.
  • Running water causes abrasion by carrying along
    loose rocks and other particles that scrape
    against each other and against the riverbed.
    Causes the riverbed rocks to be smooth and
    rounded.

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32
Chemical Weathering
  • The chemical makeup or mineral composition of the
    rocks is changed
  • Chemical reactions take place between the
    minerals in the rock and water, carbon dioxide,
    oxygen and acids.
  • Chemical reactions alter the internal structure
    of the original mineral and lead to the formation
    of new minerals.
  • Both chemical composition and the physical
    appearance of the rock undergo changes.
  • Minerals can be added or removed.
  • Minerals can be broken down decomposition

33
5.1 Weathering
? Chemical weathering is the transformation of
rock into one or more new compounds.
? Chemical Weathering of Granite
Weathering of potassium feldspar produces clay
minerals, soluble salt (potassium bicarbonate),
and silica in solution.
Quartz remains substantially unaltered.
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37
5.1 Weathering
? Weathering of Silicate Minerals
Produces insoluble iron oxides and clay minerals
? Spheroidal Weathering
Causes the corners and edges of rock to be more
rounded
38
Causes of Chemical Weathering
  • Water Hydrolysis
  • Change in composition when they react with water
    is called hydrolysis
  • Causes most of chemical weathering with carbon
    dioxide
  • Water can dissolve most minerals that hold rocks
    together
  • Soluble able to be dissolved in water
  • Water forms acids with certain gases in the
    atmosphere
  • Water can combine with a mineral to form a
    completely different mineral
  • Example Water Feldspar Clay (called kaolin)
  • Hydrogen ions from the water displace the
    elements potassium or calcium in feldspar.
  • Leaching water carries dissolved minerals to
    lower layers of rock.
  • Bauxite (aluminum ore) form when leaching causes
    a mineral to concentrate in a thin layer beneath
    the Earths surface.

39
Oxidation
  • Metallic elements combine with oxygen
  • Often occurs in rocks with iron-bearing minerals
  • 4Fe 3O2 ? 2Fe2O3 (rust)
  • Occurs when oxygen chemically combines with
    another substance
  • Causes the red color in a lot of the soil of the
    southwestern US.

40
Weathering of Silicates
41
Spheroidal Weathering
42
Carbonation
  • Carbonic acid forms when carbon dioxide dissolves
    in water occurs when carbon dioxide in the air
    combines with falling rain water.
  • H2O CO2 ? H2CO3
  • Carbonation carbonic acid reacts chemically
    with other substances.
  • Carbonic acid is able to dissolve certain rocks
    on or beneath the surface of the Earth
  • Carbonic acid is too weak to be harmful to humans
  • Slowly decomposes feldspars and limestone
  • Carbonic Acid Calcite (limestone) ? Calcium
    Carbonate
  • This dissolving action sometimes produces
    underground caverns

43
Reflecting lake in the Luray caverns in the
northern Shenendoah valley.
David Jones
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45
Spheroidal Weathering
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47
Sulfuric Acid Acid precipitation
  • Sulfur oxides are in the air of polluted areas
  • A byproduct of burning coal as a source of energy
  • Sulfur dioxide dissolves in rainwater to form
    sulfuric acid
  • Much stronger than carbonic acid.
  • Sulfuric acid corrodes rocks, metals and other
    materials very quickly

48
  • http//www.natgeoeducationvideo.com/film/1233/acid
    -rain

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54
  • Clingmans Dome Video

55
Plant Acids
  • Plants produce weak acids that dissolve certain
    minerals in rocks
  • Lichens and mosses produce acids

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http//www.lostateminor.com/2013/07/18/karcher-cle
ans-mt-rushmore-for-free/
58
5.1 Weathering
? Two other factors affecting the rate of
weathering are rock characteristics and climate.
1. Rock characteristics
  • Mineral composition and solubility
  • Physical features such as joints

59
5.1 Weathering
2. Climate
Temperature and moisture are the most crucial
factors.
Chemical weathering is most effective in areas
with high temperatures and abundant moisture.
60
5.1 Weathering
? Differential Weathering
Caused by variations in composition
Creates unusual and spectacular rock
formations and landforms
61
5.2 Soil
? Soil is part of the regolith that supports the
growth of plants.
Regolith is the layer of rock and mineral
fragments that covers most of Earths land
surface.
62
5.2 Soil
? Soil Composition
Soil has four major components mineral
matter, or broken-down rock humus, which is the
decayed remains of organisms water and air.
63
Composition by Volume of Good-Quality Soil
64
5.2 Soil
? Soil Texture
Texture refers to the proportions of different
particle sizes.
- Sand (large size)
- Silt
- Clay (small size)
Loam (a mixture of all three sizes) is best
suited for plant life.
65
Soil Texture
66
5.2 Soil
? Soil Structure
Soil particles clump together to give a soil
its structure.
67
5.2 Soil
? The most important factors in soil formation
are parent material, time, climate, organisms,
and slope.
1. Parent material
Residual soilparent material is the bedrock
Transported soilparent material has been
carried from elsewhere and deposited
68
Parent Material and Soils
69
5.2 Soil
2. Time
Important in all geologic processes
The longer a soil has been forming, the
thicker it becomes.
3. Climate
Greatest effect on soil formation
70
5.2 Soil
4. Organisms
Organisms influence the soil's physical and
chemical properties.
Furnish organic matter to soil
5. Slope
Angle
- Steep slopes often have poorly developed soils.
- Optimum slope is a flat-to-undulating upland
surface.
71
5.2 Soil
5. Slope
Orientation, or direction the slope is facing,
influences soil formation.
- Soil temperature
- Moisture
72
5.2 Soil
? Soil varies in composition, texture, structure,
and color at different depths. Soil horizons are
zones or layers of soil. A soil profile is a
vertical section through all the soil horizons.
The A horizon is commonly know as topsoil.
The B horizon is subsoil and contains clay
particles washed out from the A horizon.
The C horizon is between B horizon and
unaltered parent material.
73
Soil Profile
74
A Soil Profile Showing Different Horizons
75
5.2 Soil
? Three common types of soil are pedalfer,
pedocal, and laterite.
1. Pedalfer
Best developed under forest vegetation
Accumulation of iron oxides and aluminum-rich
clays in the B horizon
76
5.2 Soil
2. Pedocal
Accumulates calcium carbonate
Associated with drier grasslands
3. Laterite
Hot, wet, tropical climates
Intense chemical weathering
77
5.2 Soil
? Water erodes soil.
? Rates of Erosion
Human activities that remove natural
vegetation, such as farming, logging, and
construction, have greatly accelerated erosion.
? Sediment Deposition
Reservoirs fill with sediment.
Sediments are contaminated by pesticides and
fertilizers.
78
5.2 Soil
? Controlling Erosion
Planting rows of trees called windbreaks
  • Terracing hillsides
  • Plowing along the contours of hills
  • Rotating crops

79
5.3 Mass Movements
? The transfer of rock and soil downslope due to
gravity is called mass movement.
? Among the factors that commonly trigger mass
movements are saturation of surface materials
with water, oversteepening of slopes, removal of
vegetation, and earthquakes.
80
5.3 Mass Movements
? Geologists classify mass movements based on the
kind of material that moves, how it moves, and
the speed of movement.
? Rockfalls
A rockfall occurs when rocks or rocks
fragments fall freely through the air.
81
5.3 Mass Movements
? Slides
In a slide, a block of material moves suddenly
along a flat, inclined surface.
Slides that include segments of bedrock are
called rockslides.
? Slumps
A slump is the downward movement of a block of
material along a curved surface.
82
Heavy Rains Can Trigger Slumps
83
5.3 Mass Movements
? Flows
Flows are mass movements of material
containing a large amount of water.
Mudflows move quickly and carry a mixture of
soil, rock, and water that has a consistency of
wet concrete.
Earthflows move relatively slowly and
carry clay-rich sediment.
84
5.3 Mass Movements
? Creep
Creep is the slow, downhill movement of soil
and regolith.
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86
Creep
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