Definitions and Classification
Mechanical Weathering
Chemical weathering
Soil Development, Degradation, and Conservation
Weathering-related Mineral Resources
Erosion - Definition/ Agents of Erosion
Erosion and Landform Development
A. The
Connection between Magmatism, Weathering/Erosion and Plate
Tectonics in the Rock Cycle
-- The Endless Crustal Cycle of
Building It Up and Tearing It Down.
B. The
Great Importance of Weathering and Erosion in Shaping the Earth’s
Surface and Soils, and Its Influence upon the Climate and
Biosphere.
A. What is a Weathering? --
The physical breakdown and chemical
alteration
(decomposition) of rocks and minerals at or near Earth’s
surface.
v Two Types of Weathering
Processes
·
Mechanical
·
Chemical
B. What is Erosion? – The Removal and Transport of
Weathered Material
from the Site of Origin
v Several Types of Erosional
Agents
·
Simple
Gravity – Mass Wasting
·
Running
Water
·
Glaciers
·
Wind
·
Marine Waves
and Currents
III. Mechanical Weathering
A.What is Mechanical Weathering?
– The physical breakdown of Earth
material into
ever-smaller pieces that retain the chemical composition of
the parent material.
B. Types of Mechanical Weathering
·
Frost Action (wedging)
·
Pressure Release (jointing, exfoliation)
·
Heating/Cooling (expansion/contraction)
·
Salt
·
Organisms (wedging and grinding)
C.
Conditions Favoring Mechanical
Weathering
·
Rugged Terrain
·
Inherently Weak Rock
·
Very Cold and/or Hot Climates
·
Shorelines
· Wet
Climates
· Heavy
Forestation
D.
Good Example Localities of
Mechanical Weathering
·
Yosemite
·
Find some others
IV. Chemical
Weathering
A.
What is Chemical Weathering? – Those processes by
which rock materials are decomposed by chemical alteration of
the parent material.
B.
Agents of Chemical Weathering
·
Water
·
Atmospheric gases (mainly oxygen)
·
Acids
·
Organisms
C. Types of Chemical Weathering
·
Solution (simple dissolving of mineral ions)
·
Oxidation (mineral “rusting”)
·
Hydrolysis (water-ion/mineral-ion exchange)
·
Acid Solution (dissolving minerals with an acid)
Also called “Carbonation”
D. Factors that Affect the Rate of Chemical
Weathering
·
Particle Size
·
Mineral/Rock Structure (cleavage, joints, fractures)
·
Parent Rock Mineralogy
Ø The
Variability of Silicate Mineral Chemical Stability at
or near the Earth’s Surface
ü Olivine
- Very Unstable at surface conditions
ü Pyroxene
ü Amphibole
ü Ca-Plagioclase
ü Biotite
ü Na-Plagioclase
ü K-Feldspar
ü Muscovite
ü Quartz
ü Clay
-- Very Stable at Surface Conditions
Ø Carbonate
Minerals – Very Susceptible to Acid
· Climate – A Biggie!
Ø Hot/Wet
= Highest Rate
Ø Cold/Wet
Ø Hot/Dry
Ø Cold/Dry
= Slowest Rate
·
Biological Activity
E. Chemical Weathering Products
·
Clays – (from weathered silicates)
·
Dissolved Ions – (from all rock types)
·
Acids – (from all rock types)
F.
Good Example Localities of Chemical Weathering
·
Amazon and
·
Find some other places
V. Soil Development
A. What is a Soil? The
uppermost portion of the surface
regolith that consists of weathered rock,
air, water, and
organic material, and is supportive of vegetation.
A soil typically consists of:
·
Several layers called horizons (O, A, B, and C)
·
45% Weathered rock (sand, silt, clay)
·
55% Humus, Air and/or Water
·
Humus is decayed organic mater
·
Horizon O = Very thin top layer (mainly organic
debris)
·
Horizon A = “Topsoil”, “Zone of Leaching” – the
organic-
rich,
productive layer of the soil profile.
·
Horizon B = “Zone of Accumulation” – Organic-poor,
and
not very
productive.
·
Horizon C = Partially altered bedrock/regolith
C.
Classification of Major Soil
Types
·
Pedalfers =
Al-rich Clays +Organic-rich – Develops in
temperate wet climates (ex:
·
Pedocals = Ca/Alkali-rich + Mod/low Organics -
Develops
In warm arid/semiarid regions (ex:
·
Laterites = Extremely leached - Al/Fe-rich,
Silica-poor; All
soluble ions leached out; red color; very deep soil profiles;
Forms in the tropics (ex: Amazon)
D. Factors
That Affect Soil Development
1.
Climate – The most crucial factor, which includes the
consideration of mean temperature, precipitation, and organic
activity
Ø
Native (in place) versus Transported (exotic)
Ø
Granite versus Basalt versus Limestone
3. Terrain – Relief and Slope
Ø Steep/Rugged
versus Flat/Gentle
Ø North-facing versus South-Facing
E. Factors That Affect Soil Development
Ø
“Bioturbation” – (boring, burrowing, ingesting)
Ø
Acid-producing bio-processes
·
Time – Soil needs lots of time to development
A.
Loss and Deterioration of Soil
is a Serious Worldwide
Concern to Humans
·
Current studies estimate close to 20% of world’s
productive soils have been degradated.
·
Soil is considered a non-renewable resource
·
Most of recent soil degradation is attributed to
human
activities.
B.
Major Factors that Contribute to Soil Degradation
·
Primary Factors
Ø
Improper Farming Practices
Ø
Overgrazing
Ø
Deforestation
·
Secondary Factors
Ø
Wind
Ø Running Water
C.
Soil Conservation Practices
·
Contour Plowing
·
Terracing
·
Windbreaks
·
Strip-cropping
·
Crop-rotation
· Reduced grazing
· Open Space Preserves
VII.
Weathering-Related
·
Bauxite
(Primary aluminum ore) - Aluminum oxide/
hydroxide
deposits = Super Extreme leaching of soil
A.
What is Erosion? – The
Removal and Transport of
Weathered Material from the Site of Origin
v Several Types of Erosional
Agents
·
Simple
Gravity = Mass Wasting
·
Running
Water
·
Glaciers
·
Wind
·
Marine Waves
and Currents
B.What is Mass Wasting?
– The Downslope Removal of
Material from the
Site of Origin
v Several Types of Mass
Wasting –
v Classified According to Type
of Movement
v Rate of Movement Varies
Greatly
·
Rockfalls - Very fast
·
Landslides,
Rockslides and Slumps Fast to slow
·
Earthflows,
mudflows, Debris flows - Fast
·
Creep – Slow
to Very slow
C.Factors That Influence Mass Wasting Events
1) Slope (material) Shear
Strength
§
Geology (composition and structure)
§
Water Content
2) Slope Angle
3) Weathering and
Climate/Weather Conditions
4) Vegetation
5) Overloading
6) Temporary Disturbing Forces
– “The Last Straw”
D. Mass Wasting Triggering Mechanisms
1) Heavy
rainstorm
2) Earthquakes
3) Eruptions
4) Explosions
5) Strong
Vibrations from a loud sound
6) Slope
undercutting
E. Characteristics of the
Different Types of Mass Wasting
1) Rockfalls
·
Falling (freely) Loose Rock
·
Associated with Eroding Cliffs/Bluffs
2) Landslides, Rockslides
and Slumps
·
Solid (cohesive) Masses Move over a Glide
Surface
(planar or curved surface)
·
Characteristic “Scarps” “Hummocks & “Toes”
·
Can be Very Extensive
·
Rate of Movement can vary greatly
3) Earthflows, mudflows, Debris flows
·
Behaves like a Fluid
·
Rate of Movement Varies, but can be very fast.
·
Flows follow Low areas (drainage channels)
·
Flows can be Very Extensive
·
Closely Associated with Water saturation
4) Earth and Soil Creep
·
A Very Slow form of Flow
·
The Most Widespread form of Mass Wasting
· Difficult
to Recognize and Control
F. Mass Wasting Hazard Management
1) Importance of
Identifying Unstable Areas
·
Geology/Risk Assessment Studies
2) Create a
Slope-stability Map
3) Methods to
Reduce or Eliminate Slope Instability
·
“Cut and Fill”
·
“Benching” or “Terracing”
·
“Rock Bolting”
·
“Retaining Walls and Cribbing”
G.
Local Examples of Recent Mass
Wasting
1)
·
Black’s Beach
2)
3)
Name some other notable regions
IX. Erosion and Landforms
A. Mountains, plateaus, peneplains, plains, coastlines,
canyons, valleys, hills, mesas, buttes, rivers, lakes,
and caves.
B. The unique characteristics of each landform type.
D.Illustrations of Major Landforms.
X. Vocabulary Terms
1. Study the Vocabulary list at the end of
Chapters 5 and 14.