Weathering, Soil, and Mass Movement

What is What is Weathering?Weathering?

Is the breaking down and changing of rocks near Earth’s surface◦Two Types: Mechanical (physical) and Chemical

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.

Three Types Three Types of of

Mechanical Mechanical WeatheringWeathering

Frost Wedging

UnloadingBiological Activity

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

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

Biological Biological ActivityActivity

• The activity of organisms, including plants, burrowing animals, and humans

• Plant roots wedge into rocks breaking them apart

What is What is Chemical Chemical

Weathering?Weathering?Chemical weathering: the transformation of rock into one or more new compounds.

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.

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

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

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.

How is Soil How is Soil Formed?Formed?

Soil is formed by rock being eroded away.

Parent Parent materialmaterial

Residual soil◦ parent material is the

bedrock

Transported soil◦ parent material has

been carried from elsewhere and deposited

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

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.

Characteristics of SoilCharacteristics of Soil

CharacteristiCharacteristics of Soilcs of Soil

Soil StructureSoil particles clump together to give a soil its structure.

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.

Soil Soil ProfileProfile

O Horizon: HumusA Horizon: TopsoilE Horizon: Eluviation

layerB Horizon: SubsoilC Horizon: RegolithR Horizon: Bedrock

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

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

Processes Processes of Water of Water ErosionErosion

1. Sheet erosion - 2. Rills (tiny

streams)3. Gullies (trenches)4. Transports

sediments for deposits.

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

What is Mass What is Mass Movement?Movement?The transfer of

rock and soil down-slope due to gravity

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

Classification Classification of Mass of Mass MovementsMovements

Rockfalls occurs when rocks or rocks fragments fall freely through the air.

Classification of Classification of Mass Mass MovementsMovementsAvalanches

--extremely rapid movement of earth material or snow

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.

Classification Classification of Mass of Mass MovementsMovementsSlumps

A slump is the downward movement of a block of material along a curved surface.

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.

ClassificatioClassification of Mass n of Mass MovementsMovements

Creep is the slow, downhill movement of soil and regolith.

slowest type of mass movement