Weathering

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Mass Wasting
Erosion
Soils
Weathering
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Weathering the physical and chemical breakdown
of rock exposed to wind, water, ice, and living
organisms
Regolith loose or broken rock layers resulting
from weathering Regolith covers most of the
earth.
Soil the upper-most layer of regolith that
supports life
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Do things last for ever ? Consider
new concrete
a 1955 Chevrolet
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Rocks can be broken down or chemically altered on
the earths surface. Mechanical Weathering
Rocks are physically broken down by
various surface processes into smaller parts
without changing physical properties.
Chemical Weathering Rocks are
altered from one form to a
completely new form with a different
set of physical properties.
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I
weathering
Discuss with a friend

• Describe the difference between
• mechanical and chemical weathering.
• 2. Give two examples of MW and CW you
• have observed.

I will get an A on my exams and quizzes
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Mechanical Weathering the breaking down of rocks
How do we expose more surface area for chemical
weathering to do its job ? Lets show some
surface
Rock
More surface area
Less surface area
Increased mechanical weathering accelerates
chemical weathering.
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Frost Wedging

• Repeated cycles of freezing
• and thawing.
• Ice expands 9 of its volume.
• Rock is continually broken
• down over geologic time
• Part of the Yosemite
• weathering cycle.

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Frost Wedging rocks are broken into plates and
split apart.
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Exfoliation

• unloading of overlying rock
• material releases pressure
• expansion of granitic bodies
• causing sheeting or slabbing
• granite
• granite sheets break along
• planes of weakness or joints
• exacerbated by frost wedging
• dominant weathering force
• in Yosemite

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Exfoliation Dome granite is sheeting from
loss of pressure due to unloading processes.
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Types of Mechanical Weathering Processes

• Biological Activity breaking down rocks
  through
• animal burrowing
• humans
• plant roots

Human intervention
Animal burrowing
Plant root weathering
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I
mechanical weathering
Discuss with a friend
3. Why is MW important? 4. Briefly describe
how frost wedging, unloading and biological
activity contributes to mechanical
weathering
I will get an A on my exams and quizzes
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Chemical Weathering Rocks are chemically
altered producing a new compound

• Why would a perfectly good rock want to change
• its appearance?
• STABILITY! Rocks require stability and achieve
• equilibrium with its surroundings
• Most rocks are not chemically stable at the
• earths surface
• Minerals (compositions) change to become stable
• at surface conditions

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• What common agent can begin the process of
  chemical alteration?????
• The Universal Solvent WATER (H2O)

How would we speed up the action of water? Rain
????? What in the atmosphere is added to
water to create a weak acid? H2O (rain)
CO2 (atmosphere) H2CO3 (carbonic Acid)

Lets weather some granite with the natural acid
H2CO3
Granite the most abundant continental rock
weathering the potassium feldspar
(orthoclase)
bicarbonate
potassium
silica
orthoclase
carbonic acid
water
kaolinite clay
2KAlSi2O8 2(H HCO3) H2O
Al2Si2O5(OH)4 2K 2HCO3 4SiO2
Granite has been chemically weathered and broken
down into individual grains.
in solution
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Reduced to Clay
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Chemical weathering
Discuss with a friend
5. What is the universal solvent? 6. How is
carbonic acid naturally Produced? 7. How
would you describe the last or most
reduced material ----- the end product of
chemical weathering?
I will get an A on my exams and quizzes.
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Soil product of weathering containing solids,
liquids, and gas.
CLAY
Whats in your soil?
Loam dominant soil fraction
Humus partially decayed organic
material
CO2/Air fills the soil voids
Water wets the soil and carries high
levels of dissolved substances
SAND
SILT
50 sand, 20 silt, 30 clay Sandy Clay Loam
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• Soil Profiles
• horizons a layer of soil with
• distinctive physical and chemical
• properties.
• sequence of soil horizons from
• the surface to the underlying
• bedrock

O
A
E
O- Organic matter (humus)
A- Dark layer mixed with mineral and organic
matter
B
E- light colored layer produced from removal
of soluble material leaching
C
B- accumulation of clay
C- unweathered parent rock
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Factors that influence soil formation

• Parent Material
• residual regolith soil forms emplace or
  insitu

Soil forms and weathers emplace from parent
material.

• transported regolith regolith that is moved by
  rivers,
• wind, and ice

transported river deposits
transported regolith on Mars
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Factors that influence soil formation

• Climate soil profiles differ around the world
• which is directly influenced by
  climate
• arid soils vs. tropical soils

• Living organisms a HUGE influence on soils
• Plants make organic
  matter.
• (humus) animals mix the
  soil
• and recycle air and water.

• Topography the contour or slope of the land

• Time the longer the time the more mature a
• a soil becomes --- 1000s of years

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Classification of soils Soil Taxonomy Soil
classification is based on physical/chemical
properties of a soil
profile, influenced by climate, living
organisms, topography, and time. --- How
many different soils are there? Six categories
of soil classification order
sub-order great groups sub
groups family
series
Broadest
12-basic soil orders Names of soils are derived
from Latin/Greek. Latin solum soil Alfisols
(High-Nutrient Soil) Andisols ((Volcanic
Soil) Aridisols (Desert Soils) Entisols (New
Soils) Gelisols (Permafrost Soils) Histosols
(Organic Soils) Inceptisols (Young
Soils) Mollisols (Prairie Soils) Oxisols
(Tropical Forest Soils) Spodosols (Conifer
Forest Soils) Ultisols (Low-Nutrient
Soil) Verisols (Swelling Clay Soil)
12-orders
Specific
19,000 -series
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Distribution of Earths soils
What soil type (order) characterizes the San
Joaquin Valley?
Alfisols
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Mass Wasting
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Mass Wasting
What do these pictures have common?
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• What is Mass Wasting ?
• down-slope movement of rock,
• regolith, and soil under the direct
• influence of GRAVITY

What force acts alone to create movements of
the earth?
GRAVITY
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The role of Mass wasting Whats it good for?
Responsible for the evolution of landforms
features of the earth

• Weathering weakens rock does
• not create significant landforms
• Need mass wasting to impact
• weathering and shape significant
• earth features

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mass wasting
Discuss with a friend
8. What is mass wasting ? 9. What single
force acts alone to produce mass wasting
processes? 10. What is the sole purpose of
mass wasting?
I will get an A on my exams and quizzes.
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• So, what triggers a mass
• wasting episode allowing gravity to
• move the mass downward?
• The role of water
• Slopes to steep
• Removal of vegetation
• Earthquakes

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The Role of Water
Saturated Sand
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• The Role of Water
• Water saturates surface materials.
• Particles loose their cohesion (cant
• stick together).
• Particles slide past one another and
• slip downward under gravity forces.

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• Slopes to Steep
• steeper slopes exceed the angle of
• repose and material moves downward to
• stabilize or reach equilibrium.

• Angle of repose
• the angle at which particles are overtaken by
• gravity and move downward
• angle depends on size, shape, and moisture
  content
• of accumulated particles

Wet Sand
Dry Sand
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Over steepening exceeding the angle of repose,
nature reacts by attempting equilibrium
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• Removal of Vegetation
• where plants are lacking mass wasting
• attacking
• root systems bind soil
• where soil is removed frequent
• down slope movements occur

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• The Role of Earthquakes
• Areas that have not moved in years,
• are activated by seismic waves.

Mass slide produced by an earthquake dammed a
river forming a lake.
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How would you describe the angle of repose?
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Mass Wasting
Discuss with a friend
11. Describe the 4 triggers that enable mass
wasting process. 12. What the angle of
repose? 13. What is the most dominant trigger
causing the onset of mass wasting?
I will get an A on my exams and quizzes
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• How do geologists classify various mass wasting
  processes?
• Classification is based on

Unconsolidated debris, mud, earth
Material
Bedrock rock
Fall freefall of material Slide material moves
cohesively along well defined
surface Flow material moves down-slope as
a viscous fluid
Motion
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Mass Wasting.
Discuss with a friend
14. What two criteria do geologist use to
classify mass wasting movements?
I will get an A on my exams and quizzes
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Classification of Mass Wasting Processes
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• SLUMP
• downward movement of a sliding
• mass, rock or unconsolidated material
• that moves as a single unit along a
• curved surface
• moves very slow
• over-steepened slopes (T)
• water saturated (T)

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• Rockslide
• blocks of bedrock break loose and slide
• down a slope

Over steepness (T)

• Debris slide
• unconsolidated material break loose and
• slide down a slope

Debris slide
Rockslide
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• Debris Flow
• rapid mass movement containing soil
• and regolith with large amounts of
• water

Water saturation (T)
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• Lahars
• debris flows composed largely of volcanic
• material from the flanks
• flows down existing stream valleys
• extremely destructive events
• water saturation (T)

Lahars buried a village
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• Earth Flow
• form on hillsides in humid areas with
• abundant precipitation
• water saturated hill may break away
• under gravity and weight of soil
• water saturated (T)
• rich in clays and silt
• slow moving flows

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• Soil Creep
• the gradual downhill movement of soil and
• regolith.
• soil moves extremely slow
• soil disturbed by rain, roots
• water saturation (T)

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