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CHAPTER 14:Weathering & Erosion
SECTION 1:Weathering Process
Weathering: breaking down of rock @ Earth’s surface
Dania Beach, FL
Mechanical Weathering
■ Physically broken into pieces, composition NOT changed
■ Agents of M.W. – ice, plants & animals, gravity, running water, & wind
■ Includes exfoliation – layers peel away, result of decompression
Ice Wedging
• Water seeps into cracks &
freezes, splitting rock
further apart
• Areas – Northern US
w/winters
• Makes potholes in roads
Abrasionprocesses of
scraping away material
•Gravity, ice,
running water,
& wind
Plant & Animal Activity
• Roots of plants-grows into rock and
creates wedges
• Burrowing Animals dig, create
holes, Move soil &
expose rock
Chemical Weathering
■Break down as a result
of chemical reactions
■Changes into new
substances
■Composition &
appearance change Blue Hole – Florida – dissolved
limestone
Oxidation
• Combines with O2
• Common w/iron
minerals, red soil,
4Fe + 3O2
2Fe3O3Surface of Mars
Hydrolysis
• Many minerals react
w/water
• Leaching
• Water moves
dissolved minerals
down away from
surface Leaching
Carbonation• CO2 dissolved in air
forms carbonic acid,
H2CO3
• Minerals form
carbonates
• Limestone’s calcite
weathers easily Florida limestone caverns &
sinkholes
Organic Acids
• Formed by lichens &
mosses
• Weak acids breakdown
surfaces, seep into
cracks
Acid Precipitation
• Use of fossil fuels
makes it more acidic
• Weathers rock faster
• Clean Air Act of 1970
reduced emissions
End of Section 1 Review 1. Identify 3 agents of mechanical weathering
2. Describe how ice wedging weathers rock
3. Explain how 2 activities of plants or animals help weather rocks or soil
4. Compare mechanical and chemical weathering processes
5. Identify and describe 3 chemical processes
6. Compare hydrolysis, carbonation, and oxidation
7. Summarize how acid precipitation forms
8. Which 2 agents of weathering would be rare in a desert? Why?
9. An automobile exhaust contains nitrogen oxides. How might these pollutants affect chemical weather processes?
1. wind, water, and temperature change
2. Water seeps into crack, freezes and expands the wedge this
happens every time the freeze/thaw occurs
3. Plant root grow & expand causing wedging of rock; animal
dig burrows/holes exposing new rock to the effect of
weathering
4. Mech. Weathr. Is a physical process only – no composition
change; Chem. Weathr. Involves chemical reaction forming new
substance
5. Oxidation=iron+Oxy forms iron oxide; Hydrolysis=water + other
substance to form new subs.; Carbonation- carbonic acid forms
carbonates
6. All chemical processes involving oxygen, water & carbon
(note which combos in question 5) Hydrolysis and Carbonation
cand speed up Oxidation
7. Precipitation mixes with pollutants forming acid precip.
Occurs in greater amounts in city & manufacturing areas
8. Anything involving running water & vegetation (plants)
because both are rare in a desert
9. Nitrogen oxide is a pollutant that can mix w rain and
cause acid precipitation which can dissolve rock
structures
SECTION 2:Rates of Weathering
Differential Weathering
• Softer rocks weather
faster, based on
chemical composition
• Hard rock – ie,
Quartz resistant
Devil’s Tower – weathering & erosion of cone
Shows joints – areas of weakness
Rock Composition
• Chemical composition &
how they are cemented
together
• Limestone weathers
faster than
conglomerates &
sandstone
Amount of Exposure
• Surface area –
smaller rocks weather
faster
• Fractures & joints –
natural points of
weakness, allows easy
breaking
Climate
• Hot & cold weather
fast
• Warm & humid
weather fast
• Slowest rate – hot,
dry
Topography& Elevation
• Ice wedging & gravity more
common in high elevation
– its colder
• Water carries rock,
exposing more rock
• Gravity pulls rock down
from steep slopesAlps with mountain glacier
Human Activities andPlant & Animal Activities
■ Mining,
Construction &
Recreation
■ Plants break apart rock
■ Burrowing
■ Bats
– Guano – chemical
– Insects - mechanical
End of Section 2 Review1. Explain how rock composition affect the rate or
weathering
2. How does the surface area of a rock affect the
rate of weathering
3. Identify two ways that climate can affect the rate
of weathering
4. Describe two ways that the topography of a region
can affect the rate of weathering
5. Summarize 3 ways that human actions can affect t
he rate of weathering
6. Explain two ways that animas can affect the rate
of weathering
7. Imagine that there is an area of land where
mechanical weathering has cause damage.
Describe 2 ways to reduce the rate of mechanical
weathering
1. Rocks that contain soft material weather quickly,
rock with hard material weather slowly
2. Greater surface area can lead to more weathering
because more rock is exposed
3. Hot and cold mixed climates weather more
because of ice wedging/thawing & Warm humid
climate weather faster because of moisture
4. Higher elevations = more ice wedging & Steep
slopes = rock pulled down more by gravity
5. Mining = rock exposed to surface & chemical;
Construction = removes surface soil & exposes rock;
Biking, Hiking etc = removes surface soil & exposes rock
6. Burrowing can expose rock to weathering & animal
waste can accelerate chemical weathering
7. Plant ground cover crops (alfalfa); keep animals
from getting into the area; keep water from running
through the area.
SECTION 3:Soil
Soil Characteristics
■ Regolith – weathered rock fragments @ surface
■ Bedrock – solid unweathered rock below surface
■ Soil – mixture of minerals, water, gases, & organic material
■ Parent rock – source that forms soil
■ Residual soil – located over parent rock
■ Transported soil - eroded away from P.R.
Soil Composition
■ Mineral content
– Quartz – sandy soil
– Feldspar – clay soil
– Iron – red soils
■ Organic rich – black soils
Soil Texture
■ Types
– Clay, silt, & sand (size, sm
lg)
■ O HORIZON- This is the top layer of soil that is made up of living and decomposed materials like leaves, plants, and bugs. This layer is very thin and is usually pretty dark.
■ A HORIZON- This is the layer that we call "topsoil" and it is located just below the O Horizon. This layer is made up of minerals and decomposed organic matter and it is also very dark in color. This is the layer that many plants roots grow in.
■ B HORIZON- This is the layer that we call "subsoil" and it is located just below the A Horizon. This layer has clay and mineral deposits and less organic materials than the layers above it. This layer is also lighter in color than the layers above it.
■ C HORIZON- This is the layer that we call "regolith" and it is located just below the B Horizon. This layer is made up of slightly unbroken rock and only a little bit of organic material is found here. Plant roots are not found in this layer.
Soil HorizonsSoil is made up of distinct layers, called horizons. Each layer has its own characteristics that make it different from all of the other layers. These characteristics play a very important role in what the soil is used for and why it is important.
Soil Profiles
Soil & Climate■ Tropical Soils
– C.W. causes thick soils (laterites), leaching
occurs, little topsoil
■ Temperate Soils
– Thickest topsoil
■ Desert & Arctic Soils
– Weathering slow, thin topsoil mostly
regolith, little humus (the organic
component of soil, formed by the
decomposition of leaves and other plant
material by soil microorganisms.)
Soil & Topography
■ Soil washed downhill, soils thicker downhill & in valleys
End of Section 3 Review
1. Summarize how soil forms
2. Explain how the composition of the parent rock
affects soil composition
3. Describe three horizons of a residual soil
4. Predict the type of soil that will form in arctic and
tropical climates
5. What combination of soil and climate would be
ideal for growing deep-rooted crops? Why?
6. Would you expect crop growth to be more
successful on a farm that has uneven topography or
on a farm that has level land? Why?
7. Why would tropical soil not be good for sustained
farming?
8. Although desert and arctic climates are
extremely different, their soils may be somewhat
similar. Why?
1. Thru M & C weathering to form regolith, then into finer regolith mix with
water, and organic matter
2. Soil composition, color & texture are determined by parent rock
3. A = (topsoil) small rock & organic matter; B = (subsoil) clay &
minerals that leach from T.S; C = part. Weathered bedrock
4. Arctic = Thin soil, will little organic matter, mostly regolith; Tropical = thick soil w thin A
horizon
5. Temperate climate because it has well developed
soil and thick A horizon where plant roots grow
6. On level ground because soil is thicker on level
ground and thin on sloping ground
7. Tropical soil has thin A horizon, plant root will
use up all the nutrients in the topsoil so
harvests will become worse each time the field
is planted
8. They are similar because of low rainfall in each
climate as such reduces the rate of weathering & both
have fewer living material so the humus is lacking in
both regions.
SECTION 4:Erosion
■ Erosion – transporting weathered material, agents –gravity, wind, glacier, & water
■ Soil erosion major concern
■ Soil erodes faster than its made
■ Land use & climate affect S.E.
■ Affects crops
■ Gullying – soil washed away forms gullies, rapid erosion
■ Sheet erosion – topsoil washed away, leaves subsoil
Soil Conservation
■ Human Effects
– Farming, grazing, construction increase E. rates
■ Solutions?
– Contour farming – plowed according to shape of land
– Strip-cropping – alternating pattern of crops
– Terracing – planted in curves on slopes
– Crop rotation – alternate crops grown
– Wind Breaks – blocks the wind
Terracing Contour farming
Strip cropping
Gravity & Erosion
■ Mass movement – lg. amts. of soil flows downhill
■ Rockfalls & landslides –
– Rockfalls – from steep cliff
– Landslides – lg. mass of rock & soil quickly moves downhill
■ Mudflows – mountainous regions w/heavy rainfall or
w/ volcanic eruptions
■ Slumps – lg. mass of soil & rock that moves downhill in
1 piece
Gravity & Erosion Slump
Gravity & Erosion
■ Solifluction – arctic & mountainous areas, saturated
soil moves over frozen soil
■ Creep – slow downhill movement
– Rock fragments pile up @ base of slope - Talus
Erosion & Landforms
■ Mountains
– Mts. being uplifted have sharp peaks & narrow valleys
– Over time they wear down forming PENEPLAINS – slow rolling
hills
■ Plateaus
– lg. flat raised landform
– Dry conditions
■ Plateaus mesas buttes
Plateau, vs Mesa vs Butte: If they all have flat
tops and steep sides, why aren't they all
referred to as buttes, or mesas, or plateaus? In
laymen's terms, a butte is a small flat-topped or
pointed hill or mountain. A mesa is a medium
size flat-topped hill or mountain. And
a plateau is a really big flat-topped hill or
mountain.
Glaciers & Rivers
U-shaped V-shaped
End of Section 4 review1. What are 4 agents of erosion?
2. Summarize two processes of soil
erosion.
3. Identify 4 farming methods that result
in soil conservation
4. What are 2 ways gravity contributes to
erosion?
5. Compare rapid mass movements with
slow mass movements
6. Describe the erosion of 3 major land
forms
■ CONTINUED ON NEXT SLIDE
1. wind, water, glaciers, & gravity
2. Gullying = plowed furrows up & down a slope, rain rushes though
widening the furrow; Sheet erosion – water or wind goes over soil &
removes the top layer of soil in entire sheets
3. Contour farming, strip cropping, terracing & crop
rotation
4. Moves water down slopes & causes mass
movement of rocks and soil
5. Rapid = rockfalls, landslides, mudflows & slumping can be
catastrophic; Slow = creep & solifluction – not as catastrophic
but moves greater amount of material over time
6. Mountains are eroded from rugged peaks into
rounded slopes; plateaus are eroded into buttes and
mesas
Section 4 review continued7. Describe an experiment that could help
you determine whether a nearby hill is
undergoing creep.
8. Suppose that you wanted to grow
grapevines on a hillside in Italy. What
farming methods would you use? Why?
9. Describe 2 ways that a small butte would
change if it was in a wet climate rather than
dry climate.
10. A hillside community has asked you to
help brain storm ways to prevent future
mudflows. What are 3 methods you might
use?
7. Place a stick in the ground on a slope and monitor
its position over time (see if it changed/moved)
8. Contour planting with strip cropping between the
rows of vines or terracing to reduce hillside erosion
9. He butte would probably have shallower slopes and
more rounded tops
10. Increase ground cover to hold soil in place with the
roots of the plants; build retaining walls to hold soil
back during rain storms, do not allow building and
deforestation
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