Weathering and Erosion. Day 1 Objective: – I can explain how weathering occurs on Earth.

Weathering and Erosion

Day 1•Objective:–I can explain how weathering occurs on Earth

What is Weathering?

• Is the breaking down and changing of rocks near Earth’s surface

• Two Types–Mechanical

–Chemical

What is Mechanical Weathering?

• When physical forces break rock into smaller pieces

• Does not change the rock’s composition

• Three Ways– Frost Wedging

– Unloading

– Biological Activity

Mechanical Weathering: Frost Wedging

• Water enters cracks and crevices in rocks

• Water freezes expanding the cracks

• Eventually breaking rock into pieces

Mechanical Weathering: Unloading

• The uplift and weathering of rocks overlying igneous rocks

• Why?– Pressure on igneous

rocks is reduced causing uplift

• Exfoliation: slabs of outer rock separate and break loose

Mechanical Weathering: Biological Activity

• Activities of living organisms

• Example:–Plant roots

wedge into rocks, breaking them apart

What is Chemical Weathering?

• Is the transfer of rock into one or more new compounds

Agents of Chemical Weathering• Water– Most important agent– Picks up gases from the

atmosphere

• Oxygen– Causes oxidation of metal

minerals– Ex: rusting

• Emissions – Carbon dioxide from respiration,

sulfur dioxide and nitrogen oxides from burning fossil fuels

– Combines with water in the atmosphere to form acids like in acid rain

Chemical Weathering in Action

• Granite–Minerals turn into clay

–Washed away with water

• Spheroidal Weathering– Causes the corners and

edges of rock to be rounded

Rate of WeatheringWhat affects it?

• Rock Characteristics–Mineral composition

–Mineral solubility

• Climate– Temperature and

moisture

– Favors high temperatures and abundant moisture

• Surface areaSurface area

• Topography (slope/gravity)Topography (slope/gravity)

Day 2• ObjectiveObjective–I can explain the composition,

structure and formation of soil

What is Soil?

• Part of the regolith that supports the growth of plants

• Regolith– Layer of rock and

mineral fragments that cover most of Earth’s land surface

How is Soil Formed?

• Weathering of rocks that is carried away

• Factors– Parent Material

– Time

– Climate

– Organisms

– Slope

Soil Formation Factors

• Parent Material– Source of the mineral

matter in the soil

• Time– Important in all

geologic processes

– The longer a soil has been forming, the thicker it becomes

• Climate– Greatest effect on

soil formation

– Influences of temperature and precipitation affect rate, depth and type of weathering

• Organisms– Furnish organic

matter in soil

• Slope– Steep slopes often

have poorly developed soils

Characteristic of Soil: Soil Composition

• 45% mineral matter

• 25% air

• 25% water

• 5% humus– Decayed remains of

organisms

Characteristic of Soil:Soil Texture

• Refers to the proportions of different particle sizes– Sand (large size)

– Silt (feels like flour)

– Clay (small size)

– Loam (mix of all three; best for plants)

Soil Texture Triangle

Percent Clay

Percent Silt

Percent Sand

Texture Type

60 20 20

20 40 40

10 20 70

Characteristic of Soil: Soil Structure

• Clumping together of the particles

Day 3• Objective:Objective:–I can explain what erosion is

–I can explain how erosion works

What is Erosion?

• Removal and transport of weathered material from one location to another

Agents of Erosion

• Running Water

• Wind

• Glaciers

• Ocean currents and Waves

• Biological Organisms

What happens to the Material?

• Deposition–Materials are

dropped in another location

–Final stage of erosion

How does Water Erode Soil?

• Rain uses gravity as a force to move soil down a slope

Process of Water Erosion

1. Sheet Erosion– Thin surface of water

moving soil particles

2. Rills– Tiny streams

3. Gullies– Trenches

• Each move the soil a small distance

What is a Glacier?

• Large, moving mass of ice that forms near Earth’s poles and in mountainous regions at high elevations

How do Glaciers Erode Soil?

• Scrape and gouge out large sections of landscape

• Can carry huge rocks and piles of debris over great distance

Landforms Created by Glaciers

• Glaciated Valley– U-shaped valley

• Cirques– Bowl-shaped depression

at the head of a glaciated valley, that is surrounded on three sided by steep rock walls

• Arêtes– Snaking ridge

• Horns– Pyramid-like peaks

How does Wind Erode Soil?

• Strong in areas of little vegetation cover

• Pick up and carry sediment

• These particles batter other structures

Landscapes Shaped by Wind

• Sand Dunes–Mounds or ridges of

sand

–Wind also can cause them to move

• Loess–Windblown silt that

blankets the landscape

How can humans control erosion?

• Planting rows of trees called windbreakers

• Terracing hillsides

• Plowing along the contours of hills

• Rotating crops

Day 4• Objective:Objective:–I can explain the types of mass

movements and what causes them

–I can explain the hazard to humans they have and how to prevent them

What is Mass Movement?

• The transfer of rock and soil down-slope due to gravity

Triggers of Mass Movement

• Water– Heavy rain and rapid

snow melting saturate the surface

– Particles slide past one another easier

• Over-steepened Slopes– The steeper the slope,

the greater the chance for movement

• Removal of Vegetation–Roots keep soil intact

–Removing plants increase chances of movement and erosion

• Earthquakes–Dislodge rocks and

minerals

How to Classify Mass Movement?

• Classified by–Kind of material

moved

–How it moves

–Speed of movement

Types of Mass Movement

• Rock falls

• Slides– Rockslides

– Landslides

• Slumps

• Flows– Mudflow

– Earthflow

• Avalanches

• Creep

Rock falls

• When rock or rock fragments fall freely through the air

Slides• A block of material

moves suddenly along a flat, inclined surface

• Rockslides– Include segments of

bedrock

• Landslides–Movement of relatively

thin block of loose soil, rock and debris

Slumps

• Downward movement of block of material along a curved surface

Flows• Containing a large amount

of water which moves downslope as a thick fluid

• Mudflow– Swiftly moving mixture of

mud and water

• Earthflow–Moves relatively slow

– Carry clay-rich sediment

Avalanches

• Extremely rapid movement of Earth material or snow

Creep

• Slow, downhill movement of soil

• Only noticeable over long period of time

• Slowest type of mass movement

Preventative Actions

• Dig series of trenches to divert running water

• Constructing protective fences on highways

• Retaining walls for weak slopes

• Don’t build on steep slopes