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Weathering, Soil, and Mass Movement
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What is What is Weathering?Weathering?
Is the breaking down and changing of rocks near Earth’s surface◦Two Types: Mechanical (physical) and Chemical
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What is What is Mechanical Mechanical Weathering?Weathering?Mechanical Weathering: Physical forces break rock into smaller and smaller pieces without changing the rock’s mineral composition.
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Three Types Three Types of of
Mechanical Mechanical WeatheringWeathering
Frost Wedging
UnloadingBiological Activity
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Frost Frost WedgingWedging
Expansion of freezing water in cracks and crevices
Eventually breaking rocks into pieces
• Sections of rock that are wedged loose are called talus
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UnloadinUnloadingg
• The uplift and erosion of rocks overlying igneous rocks because pressure on igneous rocks is reduce
• Exfoliation—slabs of outer rock separate and break loose
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Biological Biological ActivityActivity
• The activity of organisms, including plants, burrowing animals, and humans
• Plant roots wedge into rocks breaking them apart
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What is What is Chemical Chemical
Weathering?Weathering?Chemical weathering: the transformation of rock into one or more new compounds.
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Agents and Agents and Evidence of Evidence of
Chemical Chemical WeatheringWeatheringWater: most important
agent of chemical and mechanical weathering. It picks up CO2 and SO2 in the air which forms acid rain.
Granite: Weathering of potassium feldspar produces clay minerals, soluble salt (potassium bicarbonate), and silica in solution. Quartz remains unaltered.
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SilicateSilicate Materials and Materials and
Spheroidal Spheroidal WeatheringWeathering
Weathering of Silicate Minerals: Produces insoluble iron oxides and clay minerals
Spheroidal Weathering: Causes the corners and edges of rock to be more rounded
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Rate of Rate of WeatheringWeathering
How fast the rocks erode
Two factors• Rock characteristics
• Mineral composition and solubility
• Climate• Temperature and
moisture• Favors high
temperature and abundant moisture
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SoilSoilSoil: part of the
regolith that supports
the growth of plants.
Regolith: layer of rock and mineral fragments that covers most of Earth’s land surface.
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How is Soil How is Soil Formed?Formed?
Soil is formed by rock being eroded away.
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Parent Parent materialmaterial
Residual soil◦ parent material is the
bedrock
Transported soil◦ parent material has
been carried from elsewhere and deposited
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Characteristics of Characteristics of SoilSoil
Soil CompositionSoil has four major
componentsA. Mineral matter
(broken-down rock)
B. Humus (decayed remains of organisms)
C. Water
D. Air
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Characteristics Characteristics of Soilof Soil
Soil TextureTexture refers to the proportions of different particle sizes.
A. Sand (large size)
B. Silt – feels like flour
C. Clay (small size)
D. Loam (a mixture of all three sizes) is best suited for plant life.
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Characteristics of SoilCharacteristics of Soil
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CharacteristiCharacteristics of Soilcs of Soil
Soil StructureSoil particles clump together to give a soil its structure.
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Time, Climate, Time, Climate, Organisms and Organisms and
SlopeSlopeTime:
Important in all geologic processes.
The longer a soil has been forming, the thicker it becomes.
ClimateGreatest effect on soil formation
OrganismsFurnish organic matter to soil
SlopeSteep slopes often have poorly developed soils.
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Soil Soil ProfileProfile
O Horizon: HumusA Horizon: TopsoilE Horizon: Eluviation
layerB Horizon: SubsoilC Horizon: RegolithR Horizon: Bedrock
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Soil TypesSoil TypesSoil Types Location Contents
Pedalfer under forest vegetation
iron oxides and aluminum-rich clays
in the B horizon
Pedocal drier grasslands Calcium carbonate
Laterite Hot, wet, tropical climates
Intense chemical weathering to the top layers of soil
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How does How does water erode water erode
the soil?the soil?Rain uses gravity
as a force to move soil.
Flash flooding and runoff of water causes erosion
Strong winds move particles
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Processes Processes of Water of Water ErosionErosion
1. Sheet erosion - 2. Rills (tiny
streams)3. Gullies (trenches)4. Transports
sediments for deposits.
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How can How can humans humans control control erosion?erosion?Planting rows of trees called windbreaks
Terracing hillsides
Plowing along the contours of hills
Rotating crops
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What is Mass What is Mass Movement?Movement?The transfer of
rock and soil down-slope due to gravity
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Triggers of Mass Triggers of Mass MovementMovement
Water Heavy rains and rapid melting of snow
Oversteepened Slopes The steeper the slope the greater the chance for movement
Removal of vegetation Roots keep the soil intact. Removing plants causes erosion
Earthquakes Aftershocks dislodges rocks causing movements
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Classification Classification of Mass of Mass MovementsMovements
Rockfalls occurs when rocks or rocks fragments fall freely through the air.
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Classification of Classification of Mass Mass MovementsMovementsAvalanches
--extremely rapid movement of earth material or snow
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Classification Classification of Mass of Mass MovementsMovementsSlidesIn a slide, a block of
material moves suddenly along a flat, inclined surface.
Slides that include segments of bedrock are called rockslides.
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Classification Classification of Mass of Mass MovementsMovementsSlumps
A slump is the downward movement of a block of material along a curved surface.
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Classification Classification of Mass of Mass
MovementsMovementsFlowsFlows are mass movements of material containing a large amount of water.Mudflows move quickly and carry a mixture of soil, rock, and water that has a consistency of wet concrete.Earthflows move relatively slowly and carryclay-rich sediment.
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ClassificatioClassification of Mass n of Mass MovementsMovements
Creep is the slow, downhill movement of soil and regolith.
slowest type of mass movement