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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