Weathering, Erosion, and Weathering, Erosion, and SoilSoil

How does How does this cartoon this cartoon

relate to relate to weathering weathering

and and erosion?erosion?

BIG BIG Idea:Idea:

Weathering and erosion Weathering and erosion are agents of are agents of changechange on on Earth’s surface.Earth’s surface.

• Weathering:Weathering: the process by the process by which rocks are broken down which rocks are broken down chemicallychemically and and physicallyphysically by by the action of water, air, and the action of water, air, and organisms.organisms.

I. WEATHERING PROCESSESI. WEATHERING PROCESSES

A.A. Mechanical Mechanical WeatheringWeathering

Strictly a Strictly a physicalphysical process process Rocks and minerals break Rocks and minerals break

into smaller piecesinto smaller pieces NoNo change to change to

chemical chemical compositioncomposition

Agents of Agents of MECHANICALMECHANICAL Weathering:Weathering:

• iceice•plants and animalsplants and animals•gravitygravity•running waterrunning water•windwind

1. 1. Ice (Frost) WedgingIce (Frost) Wedging

• water seeps water seeps into rock into rock cracks and cracks and then freezesthen freezes

What causes this to What causes this to happen?happen?

2. Pressure2. Pressure• Exfoliation:Exfoliation: outer outer

rock layers are rock layers are stripped away (like stripped away (like an onion’s layers can an onion’s layers can be peeled)be peeled)

3. Organic Activity3. Organic Activity

•Root Action: Root Action: tree tree rootsroots grow within grow within cracks in rocks and cracks in rocks and cause the rocks to cause the rocks to splitsplit

4. Abrasion4. Abrasion• The The collisioncollision of rocks with of rocks with

one another, causing them to one another, causing them to break downbreak down

• Agents of abrasion:Agents of abrasion: gravitygravity running running waterwater

windwind

wearing wearing down or down or

smoothing smoothing of a of a

material due material due to to

constant constant collisionscollisions

Wind AbrasionWind Abrasion

Water AbrasionWater Abrasion

B. B. ChemicalChemical Weathering Weathering

• Process by which rocks and Process by which rocks and minerals undergo minerals undergo changes in changes in their compositiontheir composition– Can cause some substances to Can cause some substances to

dissolvedissolve– Some new minerals formSome new minerals form– New minerals have properties New minerals have properties

different than those of original different than those of original rockrock

• What items have you seen What items have you seen rusted?rusted?

• What could you do to such What could you do to such objects to prevent or reduce objects to prevent or reduce rusting?rusting?

Agents of Agents of CHEMICALCHEMICAL Weathering:Weathering:

•WaterWater•OxygenOxygen•Carbon dioxideCarbon dioxide•Acid precipitationAcid precipitation

1.1.Hydrolysis:Hydrolysis: reacting reacting with waterwith water

2.2.Carbonation:Carbonation: carbon carbon dioxide combines with dioxide combines with water to produce water to produce carbonic acid (dissolves carbonic acid (dissolves limestone)limestone)

3.3.Oxidation:Oxidation: reacting with reacting with oxygen (rust)oxygen (rust)

• Carbonic acid Carbonic acid creates cavescreates caves

Oxidation of the iron in the Oxidation of the iron in the rock causes a rock causes a redred hue hue

• Acid precipitation (rain):Acid precipitation (rain): sulfur sulfur dioxide, carbon dioxide and dioxide, carbon dioxide and nitrogen oxides released into nitrogen oxides released into atmosphere by human atmosphere by human activities; gases combine with activities; gases combine with oxygen and water to form oxygen and water to form strong acid rainsstrong acid rains

• Plant acids:Plant acids: from decaying from decaying plantsplants

II. RATES OF II. RATES OF WEATHERINGWEATHERING

• All rocks do not weather at All rocks do not weather at the same rate (speed)…the same rate (speed)…

• Some factors that affect the Some factors that affect the rate at which rocks weather rate at which rocks weather are:are:

A. Rock CompositionA. Rock Composition

• IgneousIgneous and and metamorphicmetamorphic rocks break down more rocks break down more SLOWLYSLOWLY

• Hardest minerals resist Hardest minerals resist weathering (i.e. quartz)weathering (i.e. quartz)

• Rocks containing Rocks containing calcitecalcite weather weather QUICKLYQUICKLY

Which layer is MORE Which layer is MORE resistant to weathering? resistant to weathering?

LEAST resistant? LEAST resistant?

A

BC

D

B. Amount of ExposureB. Amount of Exposure

•time exposedtime exposed•surface areasurface area

Surface AreaSurface Area

• Which will weather faster, Which will weather faster, solid rock or crushed rock?solid rock or crushed rock?

• The The crushedcrushed rock of course! rock of course!– the large rock is tightly the large rock is tightly packed and has less surface packed and has less surface area exposedarea exposed

– the crushed rock is loosely the crushed rock is loosely packed and has packed and has moremore surface area exposedsurface area exposed

Increased surface area = Increased surface area = increased weatheringincreased weathering

C. ClimateC. Climate

• Rocks in tropical regions weather faster than rocks in dry desert areas

• More rain, humidity, wind, and temperature range = faster weathering

• Physical Physical Weathering:Weathering:

works better in works better in a cool and dry a cool and dry climateclimate

• Chemical Chemical Weathering:Weathering:

works better in works better in a hot and a hot and moist moist environmentenvironment

(more water = (more water = more more weathering)weathering)

Cleopatra’s Needle stood in Cleopatra’s Needle stood in Egypt (hot/dry) for 3,000 Egypt (hot/dry) for 3,000 years…years…

• It was only in New It was only in New York City for 100 York City for 100 years years

• Rain, ice, and Rain, ice, and pollution destroyedpollution destroyed

itit

Compare the two Compare the two tombstones in the next tombstones in the next picture… picture…

How do they compare in How do they compare in appearance? appearance?

Which appears more Which appears more weathered?weathered?

marblemarble slateslate

marblemarble slateslate

Which tombstone is Which tombstone is older?older?

marblemarble slateslate

This means that rocks can weather at This means that rocks can weather at different rates! different rates!

D. TopographyD. Topography

•Higher elevation = faster weathering (colder, more ice wedging)

•Steep slopes - gravity pulls rocks down hill

III. Weathering and SoilIII. Weathering and Soil

Soil:Soil: loose rock loose rock fragments and fragments and clay from clay from weathered weathered rock mixed rock mixed with organic with organic material.material.

A. Soil CompositionA. Soil Composition

A = Humus - dark organic material

B & C = Soil – mixture of minerals, gases, and dead organisms

D = Regolith – layer of weathered rock fragments

E = Bedrock – solid unweathered rock

B. Soil ProfileB. Soil ProfileSoil Profile:Soil Profile: cross section of the soil cross section of the soil

layerslayers

Horizons:Horizons: layers in layers in the soil the soil

Two Types of Soil:Two Types of Soil:

1.1. Residual:Residual: parent material is parent material is the local bedrockthe local bedrock

2.2. Transported:Transported: develops from develops from parent material that has parent material that has been moved far from been moved far from original locationoriginal location

Residual SoilsResidual Soils

• forms from the weathering of the forms from the weathering of the underlying bedrockunderlying bedrock

Transported Soils Due to…Transported Soils Due to…

IV. EROSIONIV. EROSION

• Process by which the Process by which the products of weathering are products of weathering are TRANSPORTEDTRANSPORTED (moved) (moved)

• AgentsAgents of erosion: of erosion:•running WATERrunning WATER•windwind•glaciers (ice)glaciers (ice)

A. Gravity and ErosionA. Gravity and Erosion

• Talus:Talus: rockrock

fragments fragments at theat the

base of a base of a slopeslope

Mass MovementsMass Movements

Rock fall:Rock fall: fall of rocks from fall of rocks from a steep cliffa steep cliff

Landslide: Landslide: loose soil and rocks loose soil and rocks that move down the slope of a that move down the slope of a

hillhill

Mudflow:Mudflow: rapid movement of rapid movement of a large mass of muda large mass of mud

Avalanche: Avalanche: a mass of snow, a mass of snow, ice, and rocks falling rapidly ice, and rocks falling rapidly

down a mountainside.down a mountainside.

Creep:Creep: slowslow downhill downhill movement of rocks and soilmovement of rocks and soil

B. Landforms and B. Landforms and ErosionErosion

• 3 major landforms:3 major landforms:– MountainsMountains: steep, high : steep, high elevationselevations

– PlainsPlains: flat or gently sloped, : flat or gently sloped, not high above sea levelnot high above sea level

– PlateausPlateaus: high elevations, : high elevations, flat surfacesflat surfaces