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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
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
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
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
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
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
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
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
Creep
• Slow, downhill movement of soil
• Only noticeable over long period of time
• Slowest type of mass movement