Weathering and erosion shape Earth's surface through physical and chemical processes. Weathering breaks down rocks and minerals through mechanical and chemical processes. Mechanical weathering breaks rocks into smaller pieces without changing their composition, while chemical weathering alters the chemical makeup of rocks and minerals. Erosion transports weathered materials from their source, most commonly by water, wind, ice or gravity. Mass wasting specifically refers to the downslope movement of earth materials under the force of gravity by various processes such as rock falls, debris flows, slides and slumps. Factors like steep slopes, water saturation, earthquakes and removal of vegetation can make areas more prone to mass wasting.

1. WEATHERING
AND EROSION

2. WEATHERING AND EROSION
Weathering - processes at or near Earth’s
surface that cause rocks and minerals to
break down
Erosion - process of removing Earth materials
from their original sites through weathering
and transport

3. WEATHERING AND EROSION
Weathering produces regolith (“rock blanket”) which is
composed of small rock and mineral fragments. A loose layer
of fragments that covers much of Earth’s surface.
When organic matter is mixed into this material it is called
soil. The uppermost layer of regolith, which can support
rooted plants.

4.  Joints
 A fracture of rock , along
which no appreciable
movement has occurred
 Abrasion
 The gradual wearing down of
bed rock by the constant
battering of loose particles
transported by wind, water or
ice
The jointing in these rocks has
exposed new surface area which
has broken and smoothed due to
wind, water and ice.

5. WEATHERING-THE FIRST STEP IN THE
ROCK CYCLE
 How rocks disintegrate
 Weathering
 The chemical and physical
breakdown of rock exposed to air,
moisture and living organisms
The rock in the photo has weathered
in place with little erosion, forming
soil

6. WEATHERING
Mechanical Weathering - processes that break a
rock or mineral into smaller pieces without
altering its composition
Chemical Weathering - processes that change the
chemical composition of rocks and minerals

7. PROCESSES AND AGENTS OF MECHANICAL
WEATHERING
These are actions or things that break down Earth
materials
 frost wedging
 thermal expansion and contraction
 mechanical exfoliation
 abrasion by wind, water or gravity
 plant growth

8. PROCESSES AND AGENTS OF
MECHANICAL WEATHERING
Frost Wedging – cracking of rock
mass by the expansion of water
as it freezes in cracks
http://www.uwsp.edu/geo/faculty/ozsvath/images/frost%20wedging.jpg

9. FROST WEDGING (IN SOIL)
Ice crystals

10. PROCESSES AND AGENTS OF
MECHANICAL WEATHERING
Thermal expansion and
contraction –
repeated heating and cooling
of materials cause rigid
substances to crack and
separate
http://content.answers.com/main/content/wp/en-commons/thumb/d/dc/250px-Weathering_freeze_thaw_action_iceland.jpg

11. PROCESSES AND AGENTS OF
MECHANICAL WEATHERING
Exfoliation – As underlying rock
layers are exposed, there is less
pressure on them and they
expand. This causes the rigid
layers to crack and sections to
slide off. The expanding layers
often form a dome.

12. DOME EXFOLIATION

13. PROCESSES AND AGENTS OF
MECHANICAL WEATHERING
Abrasion – Moving sediments or
rock sections can break off
pieces from a rock surface they
strike. The sediments can be
moved by wind or water and the
large rock sections by gravity.

14. WIND ABRASION
http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/images/lithosphere/eolian/rock_wind_abrasion_p0772932441_NRCS.jpg

15. WIND AND WATER ABRASION
http://www.gsi.ie/Education/European+Landscapes/United+Kingdom.htm Photo Ref: P211442, "IPR/52-34CW BGS©NERC

16. PROCESSES AND AGENTS OF
MECHANICAL WEATHERING
Plant Growth – As plants such as
trees send out root systems, the
fine roots find their way into
cracks in the rocks. As the roots
increase in size, they force the
rock sections apart, increasing
the separation and weathering.

17. PLANT WEDGING

18. PROCESSES OF CHEMICAL WEATHERING
dissolving (dissolution)
oxidation
hydrolysis

19. PROCESSES OF CHEMICAL WEATHERING
Dissolving (dissolution)
Water, often containing acid from
dissolved carbon dioxide, will
dissolve minerals from a rock body
leaving cavities in the rock. These
cavities may generate sinkholes or
cave features such as stalactites
and stalagmites.

20. CHEMICAL WEATHERING
 Dissolution
 The separation of
materials into ions in a
solution by a solvent,
such as water or acid
 Rainwater acts as
weak solution of
carbonic acid
 Anthropogenic actions
influence acidity of
rainwater
The marble grave marker has been attacked
by acidic rain because of the calcite
composition. The grave marker on the right,
while old, has not been dissolved because of
its granite composition

21. CARBON DIOXIDE
 Carbon dioxide dissolves in
rain water and produces
Carbonic acid.
This Carbonic
acid easily
weathers
marble and
Limestone.

22. PROCESSES OF CHEMICAL WEATHERING
Oxidation
Minerals may combine with
oxygen to form new minerals
that are not as hard. For
example, the iron-containing
mineral pyrite forms a rusty-
colored mineral called limonite.

23. PYRITE OXIDATION
http://www.windows.ucar.edu/earth/geology/images/pyrite_sm.jpg
http://www.dkimages.com/discover/previews/965/75014124.JPG
Pyrite
Limonite

24. OXYGEN
Water + Oxygen
+Iron = RUST
When water and
oxygen mix with
Iron it creates
rust. This is
called oxidation.

25. PROCESSES OF CHEMICAL WEATHERING
Hydrolysis
Minerals may chemically
combine with water to form new
minerals. Again these are
generally not as hard as the
original material.

26. FELDSPAR HYDROLYSIS
http://www.mii.org/Minerals/Minpics1/Plagioclase%20feldspar.jpg
http://www.uwm.edu/Course/422-100/Mineral_Rocks/kaolinite1.jpg
Feldspar Kaolinite (clay)

27. FACTORS IN CHEMICAL WEATHERING
Climate – wet and warm maximizes
chemical reactions
Plants and animals – living
organisms secrete substances that
react with rock
Time – longer contact means
greater change
Mineral composition – some
minerals are more susceptible to
change than others

28. EROSION TRANSPORT AGENTS OR
FORCES
 Water
rain
streams and rivers
ocean dynamics
ice in glaciers
 Wind
 Gravity

29. STREAMS
Flowing water will lift and carry small
sediments such as silt and sand.

30. STREAM EROSION AND DEPOSITION
Where water moves more swiftly there will be more
erosion.
Where the water slows down, sediments will be
deposited.

31. OCEAN DYNAMICS
 Tidal action and waves carry away
weathered materials.
http://www.dkimages.com/discover/previews/1000/50195183.JPG
http://edge.tamu.edu/waves2001/PC_tour/erosion_files/image002.jpg

32. GLACIERS
Glaciers are large ice fields that slowly
flow downhill over time.
http://images.encarta.msn.com/xrefmedia/sharemed/targets/images/pho/t628/T628797A.jpg

33. GLACIERS
Glacial ice drags rocky material that
scours the surface it flows over . The
glacier deposits debris as it melts.
http://www.geology.um.maine.edu/user/Leigh_Stearns/teaching/kelley_island.jpg

34. WIND TRANSPORT OF SEDIMENTS
Wind will carry fine, dry sediments over
long distances.

35. WIND TRANSPORT OF DUST
Photo shows Sahara Desert sand being transported over
the Atlantic Ocean.

36. TRANSPORT BY GRAVITY
When sediments are weathered they may be
transported downward by gravity. The
general term for this is mass wasting.
http://en.wikipedia.org/wiki/Mass_wasting

37. TRANSPORT BY GRAVITY
When sediments are weathered they may be
transported downward by gravity as a slump.
Slump
http://new.filter.ac.uk/database/image.php?id=594

38. TRANSPORT BY GRAVITY
Loose sediments transported by gravity are called
scree.
Scree field
http://www.dave-stephens.com/scrambles/banff/aylmer/aylmer013.jpg

39. DEPOSITION FORMATION
Transported sediments are deposited in
layers and generate strata like those found
in the Grand Canyon.

40. DEPOSITION FORMATION

41. FACTORS AFFECTING WEATHERING
 Tectonic setting
 Young, rising mountains
weather relatively rapidly
 Mechanical weathering
most common

42. FACTORS AFFECTING WEATHERING
 Rock composition
 Minerals weather at
different rates
 Calcite weathers
quickly through
dissolution
 Quartz is very
resistant to chemical
and mechanical
weathering
 Mafic rocks with
ferromagnesian
minerals weather more
easily

43. FACTORS AFFECTING WEATHERING
 Rock structure
 Distribution of
joints influence rate
of weathering
 Relatively close joints
weather faster

44. FACTORS AFFECTING WEATHERING
 Topography
 Weathering occurs
faster on steeper
slopes
 Rockslides

45. FACTORS AFFECTING WEATHERING
 Vegetation
 Contribute to
mechanical and
chemical weathering
 Promotes weathering
due to increased water
retention
 Vegetation removal
increases soil loss
Vegetation can both hold water
And increase weathering. If removed
Rocks may also be vulnerable to abrasion

46. FACTORS AFFECTING WEATHERING
 Biologic activity
 Presence of bacteria
can increase
breakdown of rock

47. FACTORS AFFECTING WEATHERING
 Climate
 Chemical weathering is
more prevalent in warm,
wet tropical climates
 Mechanical weathering less
important here
 Mechanical weathering is
more prevalent in cold,
relatively dry regions
 Chemical weathering occurs
slowly here
Note: temperate regions such as at the
center of the chart undergo both
chemical and mechanical
weathering, i.e. New York area

48. FACTORS AFFECTING WEATHERING:
COLOR DOTS ON MAP MATCH COLORS ON CHART

49. PRODUCTS OF WEATHERING
 Clay
 Tiny mineral particles of any kind that have physical
properties like those of the clay minerals
 Clays are hydrous alumino-silicate minerals

50. PRODUCTS OF WEATHERING
 Sand
 A sediment made of relatively
coarse mineral grains
 Soil
 Mixture of minerals with
different grain sizes, along with
some materials of biologic
origin
 Humus
 Partially decayed organic
matter in soil

51. Landslides & Mass Wasting

52. Earth’s Surface is shaped by external processes…

53. Earth’s Surface is shaped by external processes…
In sculpting the Earth’s surface,
the two most important agents
of erosion are :
1) Mass wasting
2) Running water

54. PP.490-491
original artwork by Gary Hincks
There are a wide variety of manifestations
of the downslope movement of materials
by gravity, some faster and some slower.
All of these processes have destructive effects…

55. Mass Wasting: Downslope,
mass movement of Earth materials
Driven by: The pervasive background force of
…GRAVITY…
Contributing factors:
 Saturation of sediments by water
 Over-steepened slopes
 Removal of vegetation
 Earthquakes
Water fills pore spaces between sediment grains,
reduces internal resistance, adds weight.
Plants add slope stability by
protection against erosion.
Strong ground vibrations.
Slopes become unstable once they reach the angle of repose =
The steepest angle a slope can attain without slumping.

56. Stability against
gravity depends
on the strength
of a material,
which can be
represented
by its angle of
repose…
In sediments, this
angle depends on
grain and sorting.

57. In sediments, the angle of repose depends on
grain size and sorting of materials…

58. Mass Wasting
 Types of materials:
Types of movement:
 Rates of movement:
Soil/regolith -or- Rock/bedrock
Rock Falls - Free-fall of material
Rock/Debris Slides - Coherent slabs
slide along fracture surfaces
Mudflows - Soil and rock mixes with water
and becomes fluidized.
Earth or Debris Flows - Materials
move as a viscous mass.
Fastest - Rock falls & avalanches.
Avalanches “float” on
entrapped air.
Slowest - Creep (cm/year).
Talus slopes

59. FIG. 16.12
W. W. Norton
Types of mass wasting processes arrayed
by typical velocity of movement….

60. FIG. 16.12
W. W. Norton
Rock Fall/Debris Fall

61. Rock/Debris FallsMASS
WASTING
Blocks of bedrock break free, and fall from a
steep cliff face.
Contributing factors:
- Steep slopes.
- Rocks loosened along joint fractures…
…by expansion of water on freezing,
…by thermal expansion/contraction,
…by biological activity (e.g. root growth)
- Ground shaking during earthquakes.

62. FIG. 16.14
Stephen Marshak

63. FIG. 16.15
W. W. Norton

64. FIG. 16.22
W. W. Norton

65. FIG. 16.27 HI
W. W. Norton
Steps to mediate…

66. W. W. Norton
Mediation…

67. FIG. 16.08
Stephen Marshak

68. Mediation by terracing

69. FIG. 16.12
W. W. Norton
Avalanches

70. Peruvian Valley Rock Avalanche, May 1970
Before After

71. FIG. 16.12
W. W. Norton
Rock/debris slides

72. Rock Slides…
Beds dip downslope.

73. Rock SlideMASS
WASTING
Blocks of bedrock break free, and slide down
slope along a fracture surface.
Often occurs where strata are inclined, with slip
occurring along bedding planes of weak units,
like shales.
Other important contributing factors:
- Slopes become undercut by stream
or wave erosion.
- Rain or melting snow seeps into deposits and
lubricates a slip surface.
Often deadly!
If materials are unconsolidated called a
“debris slide”.

74. FIG. 16.18
W. W. Norton

75. Common
triggering
mechanism:
Saturation
(water)
of a weak,
expansive,
clay-rich
shale unit.

76. FIG. 16.20 A
W. W. Norton
Common triggering mechanism…undercutting
of slopes by streams or waves…

77. Rock slides can
develop in any type of rock
where there is are preferred
planes of weakness
dipping downslope…
Sedimentary Metamorphic Igneous
Jointing may facilitate process.

78. Mediation…

79. FIG. 16.12
W. W. Norton
Mudflow/Debris Flow

80. Mudflow / Debris Flow:
Common in high rainfall areas
where fine materials mobilized
by abundant water…

81. FIG. 16.12
W. W. Norton
Slumps

82. Slumps: Rotational TypeMASS WASTING
 Mass of material slides downward along
a curved surface (slump surface)
 Speed is usually intermediate
and material doesn’t travel very far.
 Slumping often involves several masses
that move separately (along diferent
slump planes).
 Common in weak, water saturated sediments
that are over-steepened.
 Common in coastal areas where sea cliffs
are constantly removed by wave erosion.

83. FIG. 16.04 B
Morphology of a Rotational Slump

84. Rotational Slump: Headwall shows evidence of
backward rotation.

85. FIG. 16.27 F
W. W. Norton
Approaches to mediation…

86. Earthquake-triggered slumps, Alaska EQ 1964

87. Earth/Debris Flow

88. Slumps: Earth/Debris Flow TypeMASS
WASTING
 Common in
high rainfall
areas.
 Occur on hillsides.
Develop in rock units
rich in clay/silt.
 Slow rate of movement.
 Stabilized by “toe” and
by “dewatering”.
Destructive!

89. Robert L. Schuster/U.S. Geological Survey

90. W. W. Norton
Stabilization of slumps
with plant cover…

91. FIG. 16.27 D
W. W. Norton
Stabilization by terracing…

92. FIG. 16.27 C
W. W. Norton
Stabilization by lowering
water table…

93. FIG. 16.27 B
W. W. Norton
Reduce slope angle…

94. FIG. 16.12
W. W. Norton
Creep

95. Soil/Regolith CreepMASS
WASTING
 Creep
- Slow (cm/year) downhill movement of material.
- Driven by alternate expansion/contraction of
material during freeze/thaw or cycles of wetting/drying.

96. Gravitational force acts on
rocks/soil to move them downslope…

97. FIG. 16.02 B
W. W. Norton

98. FIG. 16.02 A
W. W. Norton
Effect of cycles of freeze-thaw
on soil/regolith creep…

99. Soil/regolith creep…

100. Soil/Regolith
Creep
Slow!
Assisted by:
“Frost heaving”
(expansion of ice
upon freezing).
Soil
Regolith

101. Evidence of soil/regolith creep…

102. FIG. 16.02 C
W. W. Norton
Tell-tell signs of soil/regolith creep…

103. Signs of soil/regolith creep…

104. FIG. 16.02 D
(c) Martin Miller

105. Signs of soil/regolith creep…

106. FIG. 16.03 A
(c) Martin Miller
Solifluction: Soil creep in high latitude, cold
climate areas where freeze-thaw is active…

107. Reducing soil creep…

108. THE SOIL
PROFILE

109. THE 6 SOIL ROLES
A Soil’s role includes:
 Serving as a foundation
 Emitting and absorbing gases
 Providing habitat
 Interacting with water
 Recycling nutrients
 Supporting human settlements

110. THE 5 FACTORS OF FORMATION
Soil is formed by…
 Parent Material: the original “Mom & Pop” soil transported from
elsewhere, usually by wind or water, at different speeds
 Climate: the amount, intensity, timing, and kind of precipitation that
breaks down parts of ecosystem (i.e. rocks, trees) into soil
 Topography: Slope and Aspect affect the angle of the land and
position toward/away from the sun that soil will be exposed to
 Biological: Plants, animals, microscopic organisms, and humans
interact with soil in different ways
 Time: the amount of time it takes for the four factors (above) to interact
with each other

111. WHAT IS A SOIL PROFILE?
 A Soil Profile is a vertical cross-section of layers of soil
found in a given area. Below are two examples of soil
profiles.

112. WHAT IS A SOIL HORIZON?
 Soil horizons are the layers in a soil profile used to classify
soil types.
 Horizons based on color, texture, roots, structure, rock
fragments, and any unique characteristic worth noting.
 Master Soil Horizons are depicted by a capital letter in the
order (from top down): O, A, B, C, and R

113. O-HORIZON
The “Organic Matter”
Horizon
 Surface-layer, at depths of 0-2 feet
 Dark in color, soft in texture
 Humus - rich organic material of
plant and animal origin in a stage
of decomposition
 Leaf litter – leaves, needles,
twigs, moss, lichens that are not
decomposing
 Several O-layers can occur in
some soils, consisting only of O-
horizons

114. A-HORIZON
“Topsoil” or “Biomantle”
Horizon
 Topmost layer of mineral soil, at
depths of 2-10 feet
 Some humus present, darker in color
than layers below
 Biomantle - most biological
productive layer; earthworms, fungi,
and bacteria live this layer
 Smallest and finest soil particles

115. B-HORIZON
The “Subsoil” Horizon
 At depths of 10-30 feet
 Rich in clay and minerals like Fe
& Al
 Some organic material may reach
here through leaching
 Plant roots can extend into this
layer
 Red/brown in color due to oxides
of Fe & clay

116. C-HORIZON
The “Regolith” Horizon
 At depths of 30-48 feet
 Made up of large rocks or lumps
of partially broken bedrock
 Least affected by weathering and
have changed the least since
their origin
 Devoid of organic matter due to it
being so far down in the soil
profile

117. R-HORIZON
The “Bedrock” Horizon
 At depths of 48+ feet
 Deepest soil horizon in the soil
profile
 No rocks or boulders, only a
continuous mass of bedrock
 Colors are those of the original
rock of the area