Weathering

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Transcript Weathering

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Weathering of Rocks
Hoodoos
Weathering in the Rock Cycle
And
Sedimentary
Rocks
Metamorphic
Rocks
Weathering/Erosion
Heat and Pressure
Magma
Sediment
Igneous
Rocks
Three Dynamic Processes of
Breaking and Removing rock
1. Weathering - the disintegration
and decomposition of rock at or
near the surface
2. Erosion
3. Mass Wasting
Types of Weathering
Mechanical – physical breakdown of
rocks.
Chemical – decomposition of rocks
by chemical reactions.
Mechanical Weathering makes smaller pieces
Mechanical Weathering
1. Frost Wedging
2. Salt Wedging
3. Biological Wedging
4. Unloading
5. Thermal Expansion
Frost Wedging
Types of Mechanical
Weathering
Frost wedging – water penetrates into
cracks, expands when it freezes.
Must have:
• Adequate moisture
• Cracks in rocks
• Freeze/thaw cycles
Salt Wedging
Types of Mechanical
Weathering
Salt wedging – growth of minerals in
cracks
• Desert environments
• Water evaporates, ions in solution
combine to form minerals
Biological
Wedging
Types of Mechanical
Weathering
Biological wedging – plant roots
penetrate into cracks causing cracks
to widen.
Must have:
• Climate hospitable for plants
• Adequate moisture and
temperature
Unloading
removal of pressure of deep burial
Unloading
Sheeting
Thermal expansion
•repeated daily heating and cooling of
rock;
•heat causes expansion; cooling causes
contraction.
Chemical Weathering
Chemical alteration of minerals.
Results in new minerals and ions in
solution.
Water and acid are essential.
Types of Chemical Weathering
Hydrolysis - any reaction in which
water participates.
1. Ion Exchange – H+ replaces other
cations.
2. Dissolution - mineral completely
dissolves, leaving only ions in solution.
3. Oxidation - reaction in which elements
gain or lose electrons (example: rust).
Carbon dioxide reacts with water to form carbonic acid (Equation 1).
Carbonic acid then dissociates to give the hydrogen ion (H+) and the
hydrogen carbonate ion (HCO3-) (Equation 2). The ability of
H2CO3 to deliver H+ is what classifies this molecule as an acid, thus
lowering the pH of a solution.
Ion Exchange
Carbon Dioxide + Rain
Becomes Acid
Dissolves Minerals
Leaves ----Clay
Carries away---
Ions
Silica
Dissolution
Certain minerals
dissolve in water
Oxidation
Iron Silicate dissolves
Iron Oxidizes
Oxidized Iron
combines with Water
Leaves Iron Oxide
Relative susceptibility
To weathering
Mineral
Residual Products
Material in Solution
Quartz
quartz grains
silica
Feldspar
clay minerals
silica, K +, Na+, Ca2+
Amphibole (hornblende)
clay minerals, limonite,
hematite
silica, Mg2+, Ca2+
Olivine
limonite, hematite
silica, Mg2+
Factors influencing Weathering Rates
1. Rock Structures – chemical/mineral
composition, Physical features
2. Topography
3. Climate
Spheroidal Weathering
Elephant Rock
State Park, MO
Results of
Weathering
Result of Weathering
Regolith – a loose layer of broken
rock and mineral fragments.
Dissolved ions
Benefits of Weathering
• Creates soil
• Produces clay, sand, and gravel
• Produces minerals
Erosion and
Transport
Erosion – transport of unconsolidated
Earth material from one place to another
Modes of Transport
1. Water
2. Wind
3. Ice
4. Gravity
Erosion by Water
Removal of regolith
Loose material is easily picked up by
flowing water.
Downcutting of stream channel
Sediments abrade stream bottom,
dislodging pieces of bedrock
Headward
Erosion
Headward
Erosion
Transport by Water
Saltation – particles move downstream in
short jumps.
Bed load – material transported by saltation
Suspended load – material carried
in water for long distances.
Transport by Water
Erosion by Wind
Deflation - Loose material can be picked
up by wind
Abrasion - Windblown sediments
can "sandblast" rocks.
Erosion by Wind
Abrasion – airborne particles chip off small
fragments of other rocks.
Transport by Wind
Same processes as water – saltation, bed
load and suspended load.
Transport by Wind
Deflation – removal of small, loose
particles. Can form desert pavement.
Erosion by Ice
Plowing – loose material is "bulldozed"
Plucking – pieces of bedrock are pried
loose.
Abrasion – pieces of rock in the ice
grind against bedrock below.
Abrasion
and
Plucking
Transport by Ice
Particle size and method of
Transport
Water – smallest particles to small
boulders.
Wind – smallest particles to sand size.
Ice – smallest particles to boulders as
big as a house.
Mass Wasting
Transport by gravity
The downslope movement of
unconsolidated Earth material due to
gravity.
•What is mass wasting?
•What causes mass wasting?
•Why is it important to know about
mass wasting?
•What can be done to control
mass wasting?
Watch for
fallen Rocks
Slope Failures - Slump
Creep
Creep
Stability reduced by:
1. Adding water to the material of a slope
2. Increasing the steepness of the slope
3. Removing material from the lower
part of the slope
4. Earthquakes
5. Removal of vegetation
•What is mass wasting?
•What causes mass wasting?
•Why is it important to know about
mass wasting?
•What can be done to control
mass wasting?
Engineering Solutions
Rock Nets
Soil Nailing
Avalanche Barriers
Switzerland