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Unit 5
Chapter 14
Weathering and Erosion
Section 1 Weathering Processes
Weathering is a slow and natural process
Weathering - ________________________________________________
_____________________________________________________
Types of Weathering
I.
II.
________________ - disintegration - smaller pieces made without
chemical change
Boulders -> pebbles
_________________ - decomposition - rock materials change in
different substances
Rocks -> Clay
MECHANICAL WEATHERING
Physically breaking down the rocks
Sheet Jointing
Granite is intrusive, formed under tremendous pressure. When exposed at
the surface the pressure is much less. The granite expands and
cracks.
Exfoliation ___________________________________________
______________________________
1. Water expands when it freezes by 10%
2. Water can enter cracks in rocks and freezes, it then expands, the cracks
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get wider (ice wedging)
3. Very important where there is a lot of freezes and thaws
4. Occurs in porous rocks
5. Makes pot holes in highways
_______________________
Abrasion occurs when rocks collide together, breakdown and wear away
each other. It is caused by gravity, ice, running water and wind.
Wind can act as a sandblaster by picking up the particles and smashing
them against something.
Water carries the particles and smashes them together.
Gravity pulls rocks down and hits them together.
Ice will wedge it, and forest fires can damage rocks too.
___________________________
Small plants (lichens & mosses) wedge rocks apart with small roots larger
plants enter these cracks, anchor themselves there and eventually
make the cracks bigger.
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Animals
Ants, earthworms and burrowing animals dig into the ground and as a result,
air and water into the ground to start weathering.
Chemical Weathering
Chemical weathering __________________________________________
__________________________________________________________.
Oxidation
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___________________________________________________________
ex. magnetite, pyrite, hornblende, mica
iron - unites with oxygen to form iron oxide (rust)
Fe + O2 -> red rust
Fe + O2 + H2 O -> brown rust
Hydrolysis
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Feldspar crumbles to make kaolin.
Carbonation
Carbon Dioxide from the air dissolves in water producing a weak acid called
carbonic acid. This reacts with calcite by dissolving it easily.
Forms underground caves because caves form in limestone, and limestone
is formed from calcite
Organic Acids
Acids from plants
Decaying plants and animals releases acids which penetrate down into the
water table to the bedrock.
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Acid Precipitation
__________________________________________________________
____________________________________________________________.
Section 2 Rates of Weathering
Different materials have different rates of weathering.
process.
Both are a slow
Differential Weathering
a.
b.
c.
___________________________________________________
________________________________________________
___________________________________________________
________________________________________________.
__________________________________________________
___________________________________________________l.
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d.
__________________________________________________
_________________________________________________
Composition of Rock
Weathering depends on what the rocks are made of
What type of rock effects the type of weathering.
Clastic Sedimentary rocks resist chemical weathering as long as the
“cement” is silica; iron and lime break down easier
Shales breakdown the easiest; they split and then crumble to form clay.
Limestone chemically breaks down easily.
Biologic Sedimentary rocks are easily weathered both chemically and
mechanically
Igneous and Metamorphic weathers in warm, moist climates
Marble resists mechanical but can be broken down by chemical action.
Amount of Exposure
The more rock surface area exposed, the more erosion there will be. A rock
broken up will weather more quickly.
Surface Area
Both chemical and physical weathering can break rocks up into smaller
pieces. ___________________________________________________
Fracture and Joints
Most rocks have natural areas of weakness which will increase the surface
area. This allows for faster weathering.
Climate
Cold, dry climate – mostly mechanical
Wet, warm climate – mostly chemical
spheroidal weathering removes the corners of rocks therefore over
time the rocks become round spheres. It takes place in humid areas,
more moisture, more chemical weathering. Very uncommon.
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Topography and Elevation
The higher the elevation the more the physical breakdown occurs. Ice
wedging will occur in higher elevations and on steep slopes you will have
loose weathered material sliding down causing abrasion.
Human Activities
Mining and construction can expose rocks to weathering. Hiking and riding
all terrain vehicles can remove the upper layers of soil exposing the
underlying rock to weather. Broken rocks will weather more quickly.
Plant and Animal Activity
Roots can break apart rocks and burrowing animals can expose surfaces
can expose rocks to weathering. Some biological wastes of animals can
chemically breakdown rocks or even attract other animals to break down
rocks.
Section 3 Soil
Regolith – _______________________________________________.
Bedrock – _______________________________________________.
Soil – loose weathered bedrock material in which plants can grow. It always
contains some organic matter combined with sand, silt or clay and
contains minerals, water and gases.
Soil Characteristics
Parent Material – ___________________________________________
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____________________________________________.
______________ – soil made from weathered bedrock.
The soils composition depends on the bedrock’s
composition.
________________ – soil comes from another place and
covers bedrock. The soils are carried by wind, glaciers and
water in rivers.
1.
2.
Soil Composition
Depend on the parent material, the more organic the darker the color.
Soil Texture
Depends on the parent material (Sizes are clays, sands and silts).
Soil Profiles
Soil Profiles
Soils differ in color, mineral composition, organic matter and texture. A
profile is made when you take a cross section from bedrock to top.
The layering of the soil is called horizons
Mature sample:
A–
topsoil
_____________________________________________________
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B-
Subsoil
_____________________________________________________
C-
________________________________________________________
Soil and Climate
Climate determines the method of weathering.
determines the composition.
The process in turn
Tropical Soil
Tropical soils contain humas on top. Mostly chemical weathering because
of the temperature. Thick horizon B.
Tropical Grassland – Deep soil profiles because of the alternating hot wet
and dry climates
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Tropical Forest – Very deep profiles because of the constant wet and hot
climate. Weathering is quick
Temperate Soils
Both Chemical and Mechanical weathering. Thickest horizon A.
Temperate Grassland – fertile for farming, not good tree growth
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Temperate Forest – fertile for farming, good tree growth
Desert and Artic Soils
Slow chemical, faster mechanical due to the lack of moisture.
Arctic – weathers rocks slow, so shallow profile
Desert – Sandy soil. A lot of erosion due to mechanical weathering.
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Soil and Topography
Thick on the top and bottom of a slope, thin on the sloped side.
Section 4 Erosion
__________________________________________________. _________
is the driving force for this movement and all movement for materials
downward. The steeper the slope, the faster the movements and the
more erosion.
Erosion –___________________________________________________
____________________________________________________________
___________________________________________________.
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Soil Erosion
Some say it is the greatest environmental problem today.
________________________________
Improper farming techniques hasten erosion. When farmers plow furrows in
the land they actually open it up to be affected by the elements.
Sheet erosion is the process when water flows over a layer of soil and
removes the topsoil.
_________________________________
Reduces soil fertility and its ability for soil to grow plants.
Soil depletion is when nutrients are removed from the soil. The soil is not
able to be used to grow a crop. To make sure that this doesn’t
happen farmers rotate crops, let the land rest for a period or use
fertilizers (which can cause eutrophication).
Salinization is when we irrigate areas that are usually dry the added minerals
in the water actually dries up the land. The left behind minerals choke out
the good nutrients making the land un-usable. Very difficult to reverse.
Soil Conservation
Leaving vegetation instead of clearing the land helps keep the topsoil.
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____________________________
Plowing in curves and not straight lines helps keep erosion down.
____________________________
Alternating lines of crops at the same time reduces depletion of nutrients.
____________________________
Using step like ridges to help reduce runoff of water which in turn removes
soil.
_______________________________
Alternating crops each season and year will help reduce over use of
nutrients and will promote replenishing them.
Gravity and Erosion
Mass movement of large areas of soil.
____________________________
Landslide is a sudden movement of rocks down the slope of a hill.
Happens on steep erosional surfaces. Mostly occurs after heavy rains
or when the snows melt in the spring.
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Lahars – (remember) when a volcano melts the snow on the mountain, it
brings with it all the ash, loose material and melted snow.
Mudflow and Slump
Slump – ___________________________________________________
_____________________________________________________.
Mudflow –___________________________________________________
_______________________________________________________
.
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Talus - accumulation of rock fragments a the base of a cliff
Soilifluction
Earth flow – A mass of weathered material that has been saturated, that
flows downhill. It is slower and less fluid than a wetter slide because it
flows over frozen or solid land.
Creep
Creep – is the slow, almost invisible movement of soil down a slope.
Causes fence posts, poles and other objects fixed in the soil to move.
Erosion and Landforms
Landforms are physical features of Earth’s surface
3 major landforms
Mountains
Plains
Plateau
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All landforms are subjected to the processes that shape the Earth. One set
lifts and creates the other breaks down the landforms.
Erosion of mountains
If the mountains are not continuously being lifted up, they will become
rounded, less sharp and lower.
Erosion of plains and plateaus
Depending on the age of the area, the plateau cans be deep stream valleys
or become rugged hill and valleys.
Plains are subjected to less erosion than plateaus because they are
relatively flat and close to sea level.