The document discusses weathering, soil formation, and erosion. It defines weathering as the breaking down of rocks on Earth's surface through mechanical or chemical processes. Mechanical weathering breaks rocks into smaller pieces without changing their chemical makeup, while chemical weathering changes the chemical makeup of rocks. The main agents of erosion that move weathered materials include gravity, wind, running water, glaciers, and waves. Erosion transports weathered materials from one location to another, while deposition is the laying down of sediments in new locations. Mass movements involve the downslope movement of loose materials due to gravity.

1. Weathering, Soil Formation,Weathering, Soil Formation,
and Erosionand Erosion
Chapters 7-8Chapters 7-8

2. 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

3. 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, whichWater 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 inPlant roots can loosen rock, make cracks larger (grass in
sidewalk)sidewalk)called root-prycalled root-pry
 Abrasion: wearing away of rocks by particles carried byAbrasion: wearing away of rocks by particles carried by
wind, water, etc.wind, water, etc.
 Rough edges of particles ‘scrape’ off parts of rocks. Rocks in aRough edges of particles ‘scrape’ off parts of rocks. Rocks in a
riverbed are scraped by moving objects in the waterriverbed are scraped by moving objects in the watertheythey
become smoothbecome smooth

4. Chemical WeatheringChemical Weathering
 What causes Chemical Weathering?What causes Chemical Weathering?
 WaterWater
 Dissolves minerals that hold rocks togetherDissolves minerals that hold rocks together (hydrolysis)(hydrolysis)
 Forms acids when mixed with gases in atmosphereForms acids when mixed with gases in atmosphere (Acid(Acid
precipitation)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 w/Combines with mineral to make new mineral (combine w/
feldspar to make clay)feldspar to make clay)
 OxidationOxidation
 Oxygen chemically reacts with something else. (Iron + OxygenOxygen chemically reacts with something else. (Iron + Oxygen
= rust) Inner rock will be diff. color than outer rock.= rust) Inner rock will be diff. color than outer rock.

5. Chemical WeatheringChemical Weathering

6. Acid Precipitation and FishAcid Precipitation and Fish

7. Chemical Weathering, cont.Chemical Weathering, cont.
 CarbonationCarbonation
 Carbon dioxide and water form a weak acid. It dissolves certainCarbon dioxide and water form a weak acid. It dissolves certain
rocks (limestone) but not strong enough to harm plants/animalsrocks (limestone) but not strong enough to harm plants/animals
 Sulfuric AcidSulfuric Acid
 caused by pollutants-they dissolve in rain to form acid rain. Itcaused by pollutants-they dissolve in rain to form acid rain. It
corrodes (wears away) rocks, metals, etc. quickly.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 mineralsPlants produce weak acids that dissolve certain minerals
(mosses) and break rocks into smaller pieces.(mosses) and break rocks into smaller pieces.

8. What affects the rate ofWhat affects the rate of
Weathering?Weathering?
 Rock composition (different rocks weatherRock composition (different rocks weather
differently)differently)
 Stable rock resists chemical weatheringStable rock resists chemical weathering
 ClimateClimate
 Ex: limestone OK in warm/dry climate; when wet-Ex: limestone OK in warm/dry climate; when wet-
weak acids weatherweak 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

9. Climate and Chemical WeatheringClimate and Chemical Weathering

10. What affects the rate ofWhat affects the rate of
Weathering?Weathering?
 Surface areaSurface area
 When rock is in small pieces, more surfaceWhen rock is in small pieces, more surface
area is available for weatheringarea is available for weathering
 Topography, other variablesTopography, other variables
 Materials on slopes are more likely to moveMaterials on slopes are more likely to move
due to gravity.due to gravity.
 This exposes underlying rock, providing moreThis exposes underlying rock, providing more
opportunities for weathering.opportunities for weathering.

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

12. ErosionErosion
 ErosionErosion
 Process by which weathered rock and soil particlesProcess by which weathered rock and soil particles
are moved form one place to anotherare moved form one place to another
 Carries away products of weatheringCarries away products of weathering
 DepositionDeposition
 Process by which sediments are laid down in newProcess by which sediments are laid down in new
locationslocations
 Final stage in the erosion processFinal stage in the erosion process
 Erosion moves materials; deposition builds newErosion moves materials; deposition builds new
landformslandforms

13. Agents of ErosionAgents of Erosion
 GravityGravity
 WindWind
 Running waterRunning water
 GlaciersGlaciers
 WavesWaves
 These are all forces that move materialsThese are all forces that move materials
from place to placefrom place to place

14. GravityGravity
 Pulls rocks and soil down slopesPulls rocks and soil down slopes
 Agent of mass movementsAgent of mass movements
 LandslidesLandslides
 MudflowsMudflows
 AvalanchesAvalanches

15. WindWind
 Major agent of erosion in hot, dry climate orMajor agent of erosion in hot, dry climate or
places with little vegetationplaces with little vegetation
 When wind erodes soil to depth that water is present,When wind erodes soil to depth that water is present,
shrubs/grasses can growshrubs/grasses can growcalled oasis (happens incalled oasis (happens in
desert)desert)
 Wind barriers (windbreaks) are used to reduceWind barriers (windbreaks) are used to reduce
effects of wind erosioneffects of wind erosion
 Trees, plants planted perpendicular to wind’s directionTrees, plants planted perpendicular to wind’s direction
 Reduces soil erosion, can trap blowing snow, protect crops,Reduces soil erosion, can trap blowing snow, protect crops,
etc.etc.

16. Running WaterRunning Water
 Water has more power than wind to moveWater has more power than wind to move
particles (exceptions are hurricane and tornadoparticles (exceptions are hurricane and tornado
winds)winds)
 When water moves faster, erosion is greaterWhen water moves faster, erosion is greater
 Erosion by running water in small channels onErosion by running water in small channels on
side of slope isside of slope is rill erosionrill erosion
 When channels become deep it evolves intoWhen channels become deep it evolves into
gully erosiongully erosion

17. Gully Erosion vs. Rill ErosionGully Erosion vs. Rill Erosion

18. GlaciersGlaciers
 Produce large-scale, dramatic effectsProduce large-scale, dramatic effects
 Have capacity to carry HUGE rocks, pilesHave capacity to carry HUGE rocks, piles
of debris over great distancesof debris over great distances
 Scratch/grind the surfaceScratch/grind the surface
 Can polish othersCan polish others
 Famous for theirFamous for their depositiondeposition

19. Plants, Animals, HumansPlants, Animals, Humans
 Materials get moved from place to placeMaterials get moved from place to place
 Digging tunnels underground (animals)Digging tunnels underground (animals)
 ExcavationExcavation
 Planting gardens, etc.Planting gardens, etc.
 Building roads, buildings, etc.Building roads, buildings, etc.

20. Mass MovementsMass Movements
 Downslope movement of loose sedimentsDownslope movement of loose sediments
and weathered rock caused by gravityand weathered rock caused 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

21. Factors that affect MassFactors that affect Mass
MovementsMovements
 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 slopeAmount of friction between material and slope
 Amount of erosion that has taken place at theAmount of erosion that has taken place at the
bottom of the slopebottom of the slope
 Mass movement occurs when the forces pullingMass movement occurs when the forces pulling
material down a slope are more than thematerial down a slope are more than the
resistance of the materialsresistance of the materials

22. Types of Mass MovementsTypes of Mass Movements
 CreepCreep
 Slow, steady downhill flow of loose, weatheredSlow, 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 areasTriggered by EQ, common in volcanic areas, sloped areas
with short periods of intense rain (CA)with short periods of intense rain (CA)

23. Types of Mass MovementsTypes of Mass Movements
 SlidesSlides
 Rapid, downslope movement that occursRapid, downslope movement that occurs
when a block of loose soil, rock, debriswhen 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 mph)Very fast movement, some up to 200km/hr (124 mph)
 RockslideRockslide
 When rock sheets move downhilWhen rock sheets move downhil
 Often caused by EQOften caused by EQ

24. Landslide: El Salvador 2000
(Earthquake)
Rockslide on Westbound I-90

25. Types of Mass MovementsTypes of Mass Movements
 SlumpsSlumps
 Happens when material in a landslide rotates while itHappens when material in a landslide rotates while it
slides downhillslides downhill
 Common after rain, leave a crescent scar on the landCommon after rain, leave a crescent scar on the land
 Happen in areas with thick soil and medium-steepHappen in areas with thick soil and medium-steep
slopeslope
 AvalancheAvalanche
 Landslide with snowLandslide with snow
 Early in winter, warm ground melts snow (it refreezes, turnsEarly in winter, warm ground melts snow (it refreezes, turns
to ice). Vibrations from EQ, etc can trigger snow on top ofto ice). Vibrations from EQ, etc can trigger snow on top of
this ice sliding down the mountainthis ice sliding down the mountain

26. SlumpsSlumps

28. Types of Mass MovementsTypes of Mass Movements
 Rock FallsRock Falls
 Occur at high elevations, steep road cuts, andOccur at high elevations, steep road cuts, and
rocky shorelinesrocky shorelines
 Cliffs become weathered, eroded, and rocksCliffs become weathered, eroded, and rocks
fall into a cone-shaped pilefall into a cone-shaped pile
 Not likely in humid areas (water promotesNot likely in humid areas (water promotes
plant growth, which lessens likelihood of rockplant growth, which lessens likelihood of rock
falls)falls)

29. 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 surfaceLowering of land surface due to removing surface
particlesparticles
 AbrasionAbrasion
 Rocks shaped by abrasion are called ventifactsRocks shaped by abrasion are called ventifacts

30. Wind DepositionWind Deposition
 Wind carries particles like sand through the airWind carries particles like sand through the air
 When something blocks their movement, theWhen 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 disruptedHuman activity in coastal regions has disrupted
dune formation/damaged sand dunesdune formation/damaged sand dunes

31. LoessLoess
 Fine, lightweight particles that have beenFine, lightweight particles that have been
carried and deposited by the windcarried and deposited by the wind

32. GlaciersGlaciers
 A moving mass of iceA moving mass of ice
 Form at Earth’s poles and in high elevationsForm 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 likeOccurs when ice is too heavy, flows down the mountain like
liquidliquid
 Continental GlaciersContinental Glaciers
 Cover a continent-sized areaCover a continent-sized area
 Thickest at centerThickest at center
 Callled Ice SheetsCallled Ice Sheets

33. Glacial ErosionGlacial Erosion
 Most powerful agent of erosion because ofMost powerful agent of erosion because of
size, weight, densitysize, weight, density
 Glaciers carve U-shaped valleys, putGlaciers carve U-shaped valleys, put
scratches/grooves on rocksscratches/grooves on rocks

34. 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 valleyGlaciers can melt and the ice recedes/water flows into the valley
 The location where the sediments get deposited is the Outwash plainThe location where the sediments get deposited is the Outwash plain
 DrumlinDrumlin
 Elongated landform caused by glacial movementElongated landform caused by glacial movement
 EskerEsker
 Winding ridges of layered sediment deposited by streams under aWinding 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 aOccurs when block of ice breaks away from a glacier, melts in a
depression. Precipitation, surface water combine with the water to formdepression. Precipitation, surface water combine with the water to form
a glacial lakea glacial lake

35. 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?

36. Soil FormationSoil Formation
 SoilSoil
 Loose covering of broken rock and humus onLoose covering of broken rock and humus on
the earth’s surfacethe earth’s surface
 Humus is decaying organic matter (leaves, etc)Humus is decaying organic matter (leaves, etc)
 Soil formation takes a very long timeSoil formation takes a very long time

37. Soil CompositionSoil Composition
 SoilSoil forms in layersforms in layers during the process of itsduring the process of its
development.development.
 TheThe parent rockparent rock is the solid bedrock from whichis the solid bedrock from which
weathered pieces of rock first break off.weathered pieces of rock first break off.
 The smallest pieces of weathered rock, along withThe smallest pieces of weathered rock, along with
living and dead organisms, remain in the very topliving and dead organisms, remain in the very top
layer.layer.
 Rainwater seeps through this top layer ofRainwater seeps through this top layer of
materials, dissolves soluble minerals, and carriesmaterials, dissolves soluble minerals, and carries
them into the lower layers of the soil.them into the lower layers of the soil.

38. Soil CompositionSoil Composition
 Residual soilResidual soil is soil located above itsis soil located above its
parent bedrock.parent bedrock.
 Transported soilTransported soil is soil that has been moved tois soil that has been moved to
a location away from its parent bedrock by agentsa location away from its parent bedrock by agents
of erosion, such as running water, wind, andof erosion, such as running water, wind, and
glaciers.glaciers.
 The parent bedrock determines what kinds ofThe parent bedrock determines what kinds of
minerals a soil contains.minerals a soil contains.
 The parent rock and climatic conditions of an areaThe parent rock and climatic conditions of an area
determine the length of time it takes fordetermine the length of time it takes for
soil to form.soil to form.

39. Soil ProfilesSoil Profiles
 What is a soil profile?What is a soil profile?
 A vertical sequence of soil layersA vertical sequence of soil layers
 AA soil horizonsoil horizon is a distinct layer, or zone,is a distinct layer, or zone,
within a soil profile.within a soil profile.
 There are three major soil horizons: A, B,There are three major soil horizons: A, B,
A, B, and C.A, B, and C.
 Horizon A contains high concentrations of organic matter andHorizon A contains high concentrations of organic matter and
humus.humus.
 Horizon B contains subsoils that are enriched withHorizon B contains subsoils that are enriched with
clay minerals.clay minerals.
 Horizon C, below horizon B and directly above solid bedrock,Horizon C, below horizon B and directly above solid bedrock,
contains weathered parent material.contains weathered parent material.
 The O horizon is organic material, that may or may not be present.The O horizon is organic material, that may or may not be present.

40. TopographyTopography
 The topography of a region affects theThe topography of a region affects the
thickness of developing soil.thickness of developing soil.
 Soils on slopes tend to be thin, coarse,Soils on slopes tend to be thin, coarse,
and infertile.and infertile.
 Soils formed in lower areas, such as inSoils formed in lower areas, such as in
valleys, are thick and fertile.valleys, are thick and fertile.

41. Soil TypesSoil Types
 Polar SoilsPolar Soils
 Form at high latitudes andForm at high latitudes and
high elevationshigh elevations
 Located in Greenland,Located in Greenland,
Canada, AntarcticaCanada, Antarctica
 No distinct horizons, veryNo distinct horizons, very
shallow soilshallow soil
 Just below the soil theJust below the soil the
ground is permanentlyground is permanently
frozen-known as permafrostfrozen-known as permafrost
Permafrost in DenaliPermafrost in Denali

42. Soil TypesSoil Types
 Temperate SoilsTemperate Soils
 Lots of variationLots of variation
 Support forests, grasslands, prairiesSupport forests, grasslands, prairies
 Amount of rainfall determines what grows inAmount of rainfall determines what grows in
this type of soilthis 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, containingForests-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

43. Soil TypesSoil Types
 Desert SoilsDesert Soils
 Very little precipitationVery 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 soilLight colored and coarse soil

44. 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 forSource of ores (iron), but not great for
growing plantsgrowing plants

45. Soil TexturesSoil Textures
 Particles of soil are classified accordingParticles of soil are classified according
to size as being clay, silt, or sand, withto size as being clay, silt, or sand, with
clay being the smallest and sand beingclay being the smallest and sand being
the largest.the largest.
 The relative proportions of theseThe relative proportions of these
particle sizes determine a soil’s texture.particle sizes determine a soil’s texture.
 The texture of a soil affects its capacityThe texture of a soil affects its capacity
to retain moisture and therefore itsto retain moisture and therefore its
ability to support plant growth.ability to support plant growth.

46. Soil TexturesSoil Textures
 To determine theTo determine the
texture of a soiltexture of a soil
sample, find itssample, find its
percent for sand,percent for sand,
silt, and clay.silt, and clay.
 The texture of theThe texture of the
soil will be where allsoil will be where all
three lines intersect.three lines intersect.

47. Soil FertilitySoil Fertility
 A measure of how well a soil can supportA measure of how well a soil can support
plant growthplant growth
 Factors involved include:Factors involved include:
 Availability of nutrients/mineralsAvailability of nutrients/minerals
 PrecipitationPrecipitation
 TopographyTopography
 AcidityAcidity
 Number of microorganisms presentNumber of microorganisms present

48. 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, associatedYellow 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