Weathering, Soil Weathering, Soil Formation, and ErosionFormation, and Erosion

Chapters 7-8Chapters 7-8

WeatheringWeathering Breaking down of rocks and other materials onBreaking down of rocks and other materials on the Earth’s surfacethe Earth’s surface

it is a slow, continuous processit is a slow, continuous process effects aren’t easily observedeffects aren’t easily observed

Two Types:Two Types: MechanicalMechanical: rocks are broken into smaller pieces but : rocks are broken into smaller pieces but

their chemical makeup does not changetheir chemical makeup does not change ChemicalChemical: chemical makeup of rocks is changed as : chemical makeup of rocks is changed as

rocks are broken downrocks are broken down

Mechanical WeatheringMechanical Weathering What causes Mechanical Weathering?What causes Mechanical Weathering? Temperature: Temperature:

Rocks expand/contract (cycle).Rocks expand/contract (cycle). Causes exfoliation (flaking) Causes exfoliation (flaking)

Frost wedging: Frost wedging: Water seeps into small cracks, freezes and expands, which Water seeps into small cracks, freezes and expands, which

enlarges cracks. (cracks in sidewalk, potholes in road)enlarges cracks. (cracks in sidewalk, potholes in road) Organic Activity: (caused by living things) Organic Activity: (caused by living things)

Plant roots can loosen rock, make cracks larger (grass in Plant roots can loosen rock, make cracks larger (grass in sidewalk)sidewalk)called root-prycalled root-pry

Abrasion: wearing away of rocks by particles Abrasion: wearing away of rocks by particles carried by wind, water, etc. carried by wind, water, etc. Rough edges of particles ‘scrape’ off parts of rocks. Rocks Rough edges of particles ‘scrape’ off parts of rocks. Rocks

in a riverbed are scraped by moving objects in the in a riverbed are scraped by moving objects in the waterwaterthey become smooththey become smooth

Chemical WeatheringChemical Weathering What causes Chemical Weathering?What causes Chemical Weathering? WaterWater

Dissolves minerals that hold rocks together Dissolves minerals that hold rocks together (hydrolysis)(hydrolysis)

Forms acids when mixed with gases in atmosphere Forms acids when mixed with gases in atmosphere (Acid precipitation)(Acid precipitation)

Acid precipitation has a ph of less than 5.6Acid precipitation has a ph of less than 5.6 Combines with mineral to make new mineral (combine Combines with mineral to make new mineral (combine

w/ feldspar to make clay)w/ feldspar to make clay) OxidationOxidation

Oxygen chemically reacts with something else. (Iron + Oxygen chemically reacts with something else. (Iron + Oxygen = rust) Inner rock will be diff. color than outer Oxygen = rust) Inner rock will be diff. color than outer rock.rock.

Chemical WeatheringChemical Weathering

Acid Precipitation and FishAcid Precipitation and Fish

Chemical Weathering, cont.Chemical Weathering, cont. CarbonationCarbonation

Carbon dioxide and water form a weak acid. It dissolves Carbon dioxide and water form a weak acid. It dissolves certain rocks (limestone) but not strong enough to harm certain rocks (limestone) but not strong enough to harm plants/animalsplants/animals

Sulfuric AcidSulfuric Acid caused by pollutants-they dissolve in rain to form acid caused by pollutants-they dissolve in rain to form acid

rain. It corrodes (wears away) rocks, metals, etc. quickly. rain. It corrodes (wears away) rocks, metals, etc. quickly.

What do you think it does to monuments and buildings?What do you think it does to monuments and buildings? Plant AcidsPlant Acids

Plants produce weak acids that dissolve certain minerals Plants produce weak acids that dissolve certain minerals (mosses) and break rocks into smaller pieces.(mosses) and break rocks into smaller pieces.

What affects the rate of What affects the rate of Weathering?Weathering?

Rock composition (different rocks Rock composition (different rocks weather differently)weather differently)

Stable rock resists chemical weatheringStable rock resists chemical weathering ClimateClimate

Ex: limestone OK in warm/dry climate; when Ex: limestone OK in warm/dry climate; when wet-weak acids weatherwet-weak acids weather

Time exposed on surfaceTime exposed on surface Old unexposed rocks-no big changesOld unexposed rocks-no big changes New exposed rocks-weather quicklyNew exposed rocks-weather quickly

Climate and Chemical Climate and Chemical WeatheringWeathering

What affects the rate of What affects the rate of Weathering?Weathering?

Surface areaSurface area When rock is in small pieces, more When rock is in small pieces, more

surface area is available for weatheringsurface area is available for weathering Topography, other variablesTopography, other variables

Materials on slopes are more likely to Materials on slopes are more likely to move due to gravity.move due to gravity.

This exposes underlying rock, providing This exposes underlying rock, providing more opportunities for weathering.more opportunities for weathering.

There is a higher rate of mechanical and There is a higher rate of mechanical and chemical weathering in Asheville than in chemical weathering in Asheville than in Phoenix. Phoenix.

ErosionErosion ErosionErosion

Process by which weathered rock and soil Process by which weathered rock and soil particles are moved form one place to anotherparticles are moved form one place to another

Carries away products of weatheringCarries away products of weathering DepositionDeposition

Process by which sediments are laid down in Process by which sediments are laid down in new locationsnew locations

Final stage in the erosion processFinal stage in the erosion process Erosion moves materials; deposition builds Erosion moves materials; deposition builds

new landforms new landforms

Agents of ErosionAgents of Erosion GravityGravity WindWind Running waterRunning water GlaciersGlaciers WavesWaves These are all forces that move These are all forces that move

materials from place to placematerials from place to place

GravityGravity Pulls rocks and soil down slopesPulls rocks and soil down slopes Agent of mass movementsAgent of mass movements

LandslidesLandslides MudflowsMudflows AvalanchesAvalanches

WindWind Major agent of erosion in hot, dry climate Major agent of erosion in hot, dry climate

or places with little vegetationor places with little vegetation When wind erodes soil to depth that water is When wind erodes soil to depth that water is

present, shrubs/grasses can growpresent, shrubs/grasses can growcalled oasis called oasis (happens in desert)(happens in desert)

Wind barriers (windbreaks) are used to Wind barriers (windbreaks) are used to reduce effects of wind erosionreduce effects of wind erosion Trees, plants planted perpendicular to wind’s Trees, plants planted perpendicular to wind’s

directiondirection Reduces soil erosion, can trap blowing snow, protect Reduces soil erosion, can trap blowing snow, protect

crops, etc.crops, etc.

Running WaterRunning Water Water has more power than wind to move Water has more power than wind to move

particles (exceptions are hurricane and particles (exceptions are hurricane and tornado winds)tornado winds)

When water moves faster, erosion is When water moves faster, erosion is greatergreater

Erosion by running water in small channels Erosion by running water in small channels on side of slope is on side of slope is rill erosionrill erosion

When channels become deep it evolves into When channels become deep it evolves into gully erosiongully erosion

Gully Erosion vs. Rill ErosionGully Erosion vs. Rill Erosion

GlaciersGlaciers Produce large-scale, dramatic effectsProduce large-scale, dramatic effects Have capacity to carry HUGE rocks, Have capacity to carry HUGE rocks,

piles of debris over great distancespiles of debris over great distances Scratch/grind the surfaceScratch/grind the surface Can polish othersCan polish others Famous for their Famous for their depositiondeposition

Plants, Animals, HumansPlants, Animals, Humans Materials get moved from place to Materials get moved from place to

placeplace Digging tunnels underground Digging tunnels underground

(animals)(animals) ExcavationExcavation Planting gardens, etc.Planting gardens, etc. Building roads, buildings, etc.Building roads, buildings, etc.

Mass MovementsMass Movements Downslope movement of loose Downslope movement of loose

sediments and weathered rock sediments and weathered rock caused by gravitycaused by gravity

A form of erosionA form of erosion Only occur on slopesOnly occur on slopes Also Known As Mass WastingAlso Known As Mass Wasting

Factors that affect MassFactors that affect MassMovementsMovements

Weight of materialWeight of material Resistance to sliding/flowingResistance to sliding/flowing Triggers such as earthquakesTriggers such as earthquakes Amount of friction between material and Amount of friction between material and

slopeslope Amount of erosion that has taken place at the Amount of erosion that has taken place at the

bottom of the slopebottom of the slope

Mass movement occurs when the forces Mass movement occurs when the forces pulling material down a slope are more than pulling material down a slope are more than the resistance of the materialsthe resistance of the materials

Types of Mass MovementsTypes of Mass Movements CreepCreep

Slow, steady downhill flow of loose, weathered Slow, steady downhill flow of loose, weathered materials such as soilmaterials such as soil

Can be just a few centimeters per yearCan be just a few centimeters per year FlowFlow

Weathered materials can “flow” like a liquidWeathered materials can “flow” like a liquid MudflowsMudflows

Swift moving mixture of mud and waterSwift moving mixture of mud and water Triggered by EQ, common in volcanic areas, sloped Triggered by EQ, common in volcanic areas, sloped

areas with short periods of intense rain (CA)areas with short periods of intense rain (CA)

Types of Mass MovementsTypes of Mass Movements SlidesSlides

Rapid, downslope movement that occurs Rapid, downslope movement that occurs when a block of loose soil, rock, debris when a block of loose soil, rock, debris separates from the bedrock underneathseparates from the bedrock underneath

LandslideLandslide Little internal mixing of materialsLittle internal mixing of materials Very fast movement, some up to 200km/hr (124 Very fast movement, some up to 200km/hr (124

mph)mph) RockslideRockslide

When rock sheets move downhilWhen rock sheets move downhil Often caused by EQOften caused by EQ

Landslide: El Salvador 2000 (Earthquake)

Rockslide on Westbound I-90

Types of Mass MovementsTypes of Mass Movements SlumpsSlumps

Happens when material in a landslide rotates while Happens when material in a landslide rotates while it slides downhillit slides downhill

Common after rain, leave a crescent scar on the Common after rain, leave a crescent scar on the landland

Happen in areas with thick soil and medium-steep Happen in areas with thick soil and medium-steep slopeslope

AvalancheAvalanche Landslide with snowLandslide with snow

Early in winter, warm ground melts snow (it refreezes, Early in winter, warm ground melts snow (it refreezes, turns to ice). Vibrations from EQ, etc can trigger snow on turns to ice). Vibrations from EQ, etc can trigger snow on top of this ice sliding down the mountaintop of this ice sliding down the mountain

SlumpsSlumps

Types of Mass MovementsTypes of Mass Movements Rock FallsRock Falls

Occur at high elevations, steep road Occur at high elevations, steep road cuts, and rocky shorelinescuts, and rocky shorelines

Cliffs become weathered, eroded, and Cliffs become weathered, eroded, and rocks fall into a cone-shaped pilerocks fall into a cone-shaped pile

Not likely in humid areas (water Not likely in humid areas (water promotes plant growth, which lessens promotes plant growth, which lessens likelihood of rock falls)likelihood of rock falls)

Wind ErosionWind Erosion Occurs in places with little precipitationOccurs in places with little precipitation SuspensionSuspension

Particles are in the air for a long period of timeParticles are in the air for a long period of time SaltationSaltation

Particles bounce aroundParticles bounce around DeflationDeflation

Lowering of land surface due to removing Lowering of land surface due to removing surface particlessurface particles

AbrasionAbrasion Rocks shaped by abrasion are called ventifactsRocks shaped by abrasion are called ventifacts

Wind DepositionWind Deposition Wind carries particles like sand through the airWind carries particles like sand through the air When something blocks their movement, the When something blocks their movement, the

sand gets depositedsand gets deposited Over time, the pile of sand becomes a duneOver time, the pile of sand becomes a dune There are different types of dunesThere are different types of dunes

Dunes are classified by shapeDunes are classified by shape Human activity in coastal regions has Human activity in coastal regions has

disrupted dune formation/damaged sand disrupted dune formation/damaged sand dunesdunes

LoessLoess Fine, lightweight particles that have Fine, lightweight particles that have

been carried and deposited by the been carried and deposited by the windwind

GlaciersGlaciers A moving mass of iceA moving mass of ice Form at Earth’s poles and in high elevations Form at Earth’s poles and in high elevations

(mountainous areas)(mountainous areas) Valley GlaciersValley Glaciers

Form in valleys of mountainous areasForm in valleys of mountainous areas Occurs when ice is too heavy, flows down the mountain Occurs when ice is too heavy, flows down the mountain

like liquidlike liquid Continental GlaciersContinental Glaciers

Cover a continent-sized areaCover a continent-sized area Thickest at centerThickest at center Callled Ice SheetsCallled Ice Sheets

Glacial ErosionGlacial Erosion Most powerful agent of erosion Most powerful agent of erosion

because of size, weight, densitybecause of size, weight, density Glaciers carve U-shaped valleys, put Glaciers carve U-shaped valleys, put

scratches/grooves on rocksscratches/grooves on rocks

Glacial DepositionGlacial Deposition MorainesMoraines

Ridges of glacial tillRidges of glacial till Till is the mix of debris carried by the glacierTill is the mix of debris carried by the glacier

Glaciers can melt and the ice recedes/water flows into the Glaciers can melt and the ice recedes/water flows into the valleyvalley The location where the sediments get deposited is the Outwash The location where the sediments get deposited is the Outwash

plainplain DrumlinDrumlin

Elongated landform caused by glacial movementElongated landform caused by glacial movement EskerEsker

Winding ridges of layered sediment deposited by streams under a Winding ridges of layered sediment deposited by streams under a glacier-eskerglacier-esker

Glacial LakeGlacial Lake Occurs when block of ice breaks away from a glacier, melts in a Occurs when block of ice breaks away from a glacier, melts in a

depression. Precipitation, surface water combine with the water to depression. Precipitation, surface water combine with the water to form a glacial lakeform a glacial lake

Soil FormationSoil Formation Soil is an important natural resourceSoil is an important natural resource It is found almost everywhere on EarthIt is found almost everywhere on Earth Exactly what is it?Exactly what is it?

Soil FormationSoil Formation SoilSoil

Loose covering of broken rock and Loose covering of broken rock and humus on the earth’s surfacehumus on the earth’s surface

Humus is decaying organic matter (leaves, Humus is decaying organic matter (leaves, etc)etc)

Soil formation takes a very long timeSoil formation takes a very long time

Soil CompositionSoil Composition Soil Soil forms in layers forms in layers during the process of its during the process of its

development. development. The The parent rock parent rock is the solid bedrock from is the solid bedrock from

which weathered pieces of rock first break off. which weathered pieces of rock first break off. The smallest pieces of weathered rock, along The smallest pieces of weathered rock, along

with living and dead organisms, remain in the with living and dead organisms, remain in the very top layer. very top layer.

Rainwater seeps through this top layer of Rainwater seeps through this top layer of materials, dissolves soluble minerals, and materials, dissolves soluble minerals, and carries them into the lower layers of the soil.carries them into the lower layers of the soil.

Soil CompositionSoil Composition Residual soilResidual soil is soil located above its is soil located above its

parent bedrock. parent bedrock. Transported soilTransported soil is soil that has been is soil that has been

moved to a location away from its parent moved to a location away from its parent bedrock by agents of erosion, such as running bedrock by agents of erosion, such as running water, wind, and glaciers.water, wind, and glaciers.

The parent bedrock determines what kinds of The parent bedrock determines what kinds of minerals a soil contains.minerals a soil contains.

The parent rock and climatic conditions of an The parent rock and climatic conditions of an area determine the length of time it takes for area determine the length of time it takes for soil to form.soil to form.

Soil ProfilesSoil Profiles What is a soil profile?What is a soil profile?

A vertical sequence of soil layersA vertical sequence of soil layers A A soil horizonsoil horizon is a distinct layer, or is a distinct layer, or

zone, within a soil profile. zone, within a soil profile. There are three major soil horizons: A, There are three major soil horizons: A,

B, A, B, and C.B, A, B, and C. Horizon A contains high concentrations of organic Horizon A contains high concentrations of organic

matter and humus. matter and humus. Horizon B contains subsoils that are enriched with Horizon B contains subsoils that are enriched with

clay minerals. clay minerals. Horizon C, below horizon B and directly above solid Horizon C, below horizon B and directly above solid

bedrock, contains weathered parent material. bedrock, contains weathered parent material. The O horizon is organic material, that may or may not be The O horizon is organic material, that may or may not be

present.present.

TopographyTopography The topography of a region affects The topography of a region affects

the thickness of developing soil. the thickness of developing soil. Soils on slopes tend to be thin, Soils on slopes tend to be thin,

coarse, and infertile. coarse, and infertile. Soils formed in lower areas, such as Soils formed in lower areas, such as

in valleys, are thick and fertile. in valleys, are thick and fertile.

Soil TypesSoil Types Polar SoilsPolar Soils

Form at high latitudes Form at high latitudes and high elevationsand high elevations

Located in Greenland, Located in Greenland, Canada, AntarcticaCanada, Antarctica

No distinct horizons, very No distinct horizons, very shallow soilshallow soil

Just below the soil the Just below the soil the ground is permanently ground is permanently frozen-known as frozen-known as permafrostpermafrost

Permafrost in Permafrost in DenaliDenali

Soil TypesSoil Types Temperate SoilsTemperate Soils

Lots of variationLots of variation Support forests, grasslands, prairiesSupport forests, grasslands, prairies Amount of rainfall determines what grows Amount of rainfall determines what grows

in this type of soilin this type of soil Grasslands-lots of humus-soil is rich and fertileGrasslands-lots of humus-soil is rich and fertile Forests-soil is less deep/less fertile, containing Forests-soil is less deep/less fertile, containing

clays and iron oxides (Eastern US)clays and iron oxides (Eastern US) Prairies-dry soil-lots of grasses and bushesPrairies-dry soil-lots of grasses and bushes

Soil TypesSoil Types Desert SoilsDesert Soils

Very little precipitation Very little precipitation High levels of saltsHigh levels of salts Limited vegetationLimited vegetation Little or no organic matterLittle or no organic matter Very thin topsoil (A horizon)Very thin topsoil (A horizon) Light colored and coarse Light colored and coarse

soilsoil

Soil TypesSoil Types Tropical SoilsTropical Soils

High temperatures, heavy rainfallHigh temperatures, heavy rainfall Soil is intensely weathered, infertileSoil is intensely weathered, infertile Source of ores (iron), but not great for Source of ores (iron), but not great for

growing plantsgrowing plants

Soil TexturesSoil Textures Particles of soil are classified Particles of soil are classified

according to size as being clay, silt, according to size as being clay, silt, or sand, with clay being the smallest or sand, with clay being the smallest and sand being the largest. and sand being the largest.

The relative proportions of these The relative proportions of these particle sizes determine a soil’s particle sizes determine a soil’s texture.texture.

The texture of a soil affects its The texture of a soil affects its capacity to retain moisture and capacity to retain moisture and therefore its ability to support plant therefore its ability to support plant growth.growth.

Soil TexturesSoil Textures To determine the To determine the

texture of a soil texture of a soil sample, find its sample, find its percent for sand, percent for sand, silt, and clay.silt, and clay.

The texture of The texture of the soil will be the soil will be where all three where all three lines intersect. lines intersect.

Soil FertilitySoil Fertility A measure of how well a soil can A measure of how well a soil can

support plant growthsupport plant growth Factors involved include:Factors involved include:

Availability of nutrients/mineralsAvailability of nutrients/minerals PrecipitationPrecipitation TopographyTopography AcidityAcidity Number of microorganisms presentNumber of microorganisms present

Soil ColorSoil Color Factors that determine soil color include:Factors that determine soil color include:

ClimateClimate Soil’s compositionSoil’s composition

Topsoil-usually dark (rich in humus)Topsoil-usually dark (rich in humus) Red/yellow soils-caused by iron minerals oxidizingRed/yellow soils-caused by iron minerals oxidizing Yellow soils are often poorly drained, associated Yellow soils are often poorly drained, associated

with environmental problemswith environmental problems Gray/bluish soils-poorly drained, constantly wet, Gray/bluish soils-poorly drained, constantly wet,

lacking in oxygenlacking in oxygen