Weathering, Erosion, and Mass-Wasting Processes Designed to meet South Carolina Department of...

Weathering, Erosion, Weathering, Erosion, and Mass-Wastingand Mass-Wasting

ProcessesProcessesDesigned to meet South Carolina Designed to meet South Carolina

Department of Education Department of Education

2005 Science Academic Standards2005 Science Academic Standards

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Table of Contents (1 of 2)Table of Contents (1 of 2) Definitions: Weathering, Erosion, and Mass-Wasting Definitions: Weathering, Erosion, and Mass-Wasting (slide 4) ((Standards: Standards: 3-3.8 ; ; 5-3.1)) Types of Weathering Types of Weathering (slide 5) ( (Standards: Standards: 3-3.8 ; ; 5-3.1))

Mechanical Weathering Mechanical Weathering (slide 6) ( (Standards: Standards: 3-3.8 ; ; 5-3.1)) Exfoliation Exfoliation (slide 7) ( (Standards: Standards: 3-3.8 ; ; 5-3.1)) Frost Wedging Frost Wedging (slide 8) ( (Standards: Standards: 3-3.8 ; ; 5-3.1)) Temperature Change Temperature Change (slide 9) ( (Standards: Standards: 3-3.8 ; ; 5-3.1)) Salt Wedging Salt Wedging (slide 10) ( (Standards: Standards: 3-3.8 ; ; 5-3.1)) Abrasion Abrasion (slide 11) ( (Standards: Standards: 3-3.8 ; ; 5-3.1))

Chemical Weathering Chemical Weathering (slide 12) ( (Standards: Standards: 3-3.8 ; ; 5-3.1)) Carbonation Carbonation (slide 13) ( (Standards: Standards: 3-3.8 ; ; 5-3.1)) Hydrolysis Hydrolysis (slide 14) ( (Standards: Standards: 3-3.8 ; ; 5-3.1)) Hydration Hydration (slide 15) ( (Standards: Standards: 3-3.8 ; ; 5-3.1)) Oxidation Oxidation (slide 16) ( (Standards: Standards: 3-3.8 ; ; 5-3.1)) Solution Solution (slide 17) ( (Standards: Standards: 3-3.8 ; ; 5-3.1))

Biological Weathering Biological Weathering (slide 18) ( (Standards: Standards: 3-3.8 ; ; 5-3.1)) Lichen, Algae, and Decaying Plants Lichen, Algae, and Decaying Plants (slide 19) ( (Standards: Standards: 3-3.8 ; ; 5-3.1)) Plant Roots Plant Roots (slide 20) ( (Standards: Standards: 3-3.8 ; ; 5-3.1)) Organism Activity: Burrowing, Tunneling, and Acid Secreting Organisms Organism Activity: Burrowing, Tunneling, and Acid Secreting Organisms

(slide 21) ((Standards: Standards: 3-3.8 ; ; 5-3.1)) Differential Weathering Differential Weathering (slide 22) ( (Standards: Standards: 3-3.8 ; ; 5-3.1))

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Table of Contents, cont. (2 of 2)Table of Contents, cont. (2 of 2) Types of Erosion Types of Erosion (slide 23) ( (Standards: Standards: 3-3.8 ; ; 5-3.1))

Fluvial Fluvial (slide 24) ( (Standards: Standards: 3-3.8 ; ; 5-3.1)) Aeolian Aeolian (slide 25) ( (Standards: Standards: 3-3.8 ; ; 5-3.1) ) Ice: Glacial and Periglacial Ice: Glacial and Periglacial (slide 26) ( (Standards: Standards: 3-3.8 ; ; 5-3.1)) Gravity Gravity (slide 27) ( (Standards: Standards: 3-3.8 ; ; 5-3.1))

Types of Mass Wasting Types of Mass Wasting (slide 28) ( (Standards: Standards: 3-3.8 ; ; 5-3.1)) Rocks Falls Rocks Falls (slide 29) ( (Standards: Standards: 3-3.8 ; ; 5-3.1)) Landslides Landslides (slide 30) ( (Standards: Standards: 3-3.8; ; 5-3.1 ) ) Debris and Mudflows Debris and Mudflows (slide 31) ( (Standards: Standards: 3-3.8 ; ; 5-3.1 ) ) Slump Slump (slide 32) ( (Standards: Standards: 3-3.8; ; 5-3.1)) Creep Creep (slide 33) ( (Standards: Standards: 3-3.8; ; 5-3.1))

Deposition Deposition (slide 34) ( (Standards: Standards: 3-3.8; ; 5-3.1)) Weathering, Erosion, and Mass Wasting in the Landscape (Weathering, Erosion, and Mass Wasting in the Landscape (slide 35)) South Carolina Science Academic Standards Grade 3 (South Carolina Science Academic Standards Grade 3 (slide 35 ; ; slide 36) Resources and References Resources and References (slide 37)

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DefinitionsDefinitions Weathering, erosion, mass-wasting, and depositional processes occur at or near Weathering, erosion, mass-wasting, and depositional processes occur at or near

the Earth’s surface and produce changes to the landscape that influence surface the Earth’s surface and produce changes to the landscape that influence surface and subsurface topography and landform development.and subsurface topography and landform development.

WeatheringWeathering is the physical disintegration or chemical alteration of rocks at is the physical disintegration or chemical alteration of rocks at or near the Earth’s surface.or near the Earth’s surface.

ErosionErosion is the physical removal and transportation of weathered material is the physical removal and transportation of weathered material by water, wind, ice, or gravity. by water, wind, ice, or gravity.

Mass wasting Mass wasting is the transfer or movement of rock or soil down slope is the transfer or movement of rock or soil down slope primarily by gravity.primarily by gravity.

DepositionDeposition is the process by which weathered and eroded materials are is the process by which weathered and eroded materials are laid down or placed in a location that is different from their source. laid down or placed in a location that is different from their source.

These processes are all very important to the rock cycle because over geologic These processes are all very important to the rock cycle because over geologic

time weathering, erosion, and mass wasting transform solid rock into sediments time weathering, erosion, and mass wasting transform solid rock into sediments and soil that result in the redeposition of material forming new sedimentary and soil that result in the redeposition of material forming new sedimentary rocks. rocks.

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Standard: 3-3.8Standard: 5-3.1

Types of WeatheringTypes of Weathering I. Mechanical (physical) weatheringI. Mechanical (physical) weathering is the physical disintegration is the physical disintegration and reduction in the size of the rocks without changing their and reduction in the size of the rocks without changing their chemical composition.chemical composition.

Examples: exfoliation, frost wedging, salt wedging, temperature Examples: exfoliation, frost wedging, salt wedging, temperature changes, and abrasionchanges, and abrasion

II. Chemical weatheringII. Chemical weathering decomposes, dissolves, alters, or decomposes, dissolves, alters, or weakens the rock through chemical processes to form residual weakens the rock through chemical processes to form residual materials. materials.

Examples: carbonation, hydration, hydrolosis, oxidation, and Examples: carbonation, hydration, hydrolosis, oxidation, and solutionsolution

III. Biological weatheringIII. Biological weathering is the disintegration or decay of rocks is the disintegration or decay of rocks and minerals caused by chemical or physical agents of and minerals caused by chemical or physical agents of organisms.organisms.

Examples: Examples: organic activity from lichen and algae, rock disintegration by plant or root growth, burrowing and tunneling organisms, and acid secretion

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I. Mechanical WeatheringI. Mechanical Weathering

Mechanical weatheringMechanical weathering is the physical disintegration is the physical disintegration and reduction in the size of the rocks without and reduction in the size of the rocks without changing their chemical composition.changing their chemical composition.

ExfoliationExfoliation Frost WedgingFrost Wedging Salt WedgingSalt Wedging Temperature ChangesTemperature Changes AbrasionAbrasion

Photo courtesy of SCGSPhoto courtesy of SCGS

Mechanical weathering processes disintegrateMechanical weathering processes disintegratemetamorphic rocks in South Carolina’s metamorphic rocks in South Carolina’s

Piedmont Region. Piedmont Region.

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Mechanical Weathering: Mechanical Weathering: ExfoliationExfoliation

Exfoliation is a mechanical weathering process whereby pressure in a rock is Exfoliation is a mechanical weathering process whereby pressure in a rock is released along parallel alignments near the surface of the bedrock and layers released along parallel alignments near the surface of the bedrock and layers or slabs of the rock along these alignments break off from the bedrock and or slabs of the rock along these alignments break off from the bedrock and move downhill by gravity.move downhill by gravity.

Exfoliation primarily occurs on intrusive igneous or metamorphosed rocks Exfoliation primarily occurs on intrusive igneous or metamorphosed rocks that are exposed at the Earth’s surface.that are exposed at the Earth’s surface.

Exfoliation can occur both very slowly or very rapidly as a form of mass Exfoliation can occur both very slowly or very rapidly as a form of mass wasting.wasting.

Large rocks characterized by exfoliation are commonly referred to as Large rocks characterized by exfoliation are commonly referred to as exfoliation domes.exfoliation domes.

Table Rock mountain in South Carolina, and Enchanted Rock in Texas are Table Rock mountain in South Carolina, and Enchanted Rock in Texas are both examples of exfoliation domes with large slabs of rock exfoliating from both examples of exfoliation domes with large slabs of rock exfoliating from the bedrock.the bedrock.

Enchanted Rock in the Texas Hill Enchanted Rock in the Texas Hill Country is an example of an Country is an example of an

exfoliation dome. As pressure is exfoliation dome. As pressure is released from the surface layer, released from the surface layer,

slabs of rock exfoliate from the dome slabs of rock exfoliate from the dome and move down slope. As they are and move down slope. As they are

transported down slope, weathering transported down slope, weathering and erosion processes break the and erosion processes break the rocks into progressively smaller rocks into progressively smaller

fragments. Overtime, each new layer fragments. Overtime, each new layer that is exposed will eventually that is exposed will eventually

exfoliate, from the bedrock.exfoliate, from the bedrock.

77Table of ContentsPhoto: SCGS


Mechanical Weathering: Frost Mechanical Weathering: Frost

WedgingWedging Frost wedging is a mechanical weathering process caused by the freeze-Frost wedging is a mechanical weathering process caused by the freeze-

thaw action of water that is trapped between cracks in the rock.thaw action of water that is trapped between cracks in the rock. When water freezes, it expands and applies pressure to the surrounding When water freezes, it expands and applies pressure to the surrounding

rock forcing the rock to accommodate the expansion of the ice. rock forcing the rock to accommodate the expansion of the ice. This process gradually weakens, cracks, and breaks the rock through This process gradually weakens, cracks, and breaks the rock through

repetitive freeze-thaw weathering cycles.repetitive freeze-thaw weathering cycles. Frost wedging generally produces angular blocks and talus material. Talus Frost wedging generally produces angular blocks and talus material. Talus

is a term used to describe weathered rock fragments deposited at the base is a term used to describe weathered rock fragments deposited at the base of a hill slope or mountain. of a hill slope or mountain.

Copyright Copyright © Bruce Molnia, USGS© Bruce Molnia, USGS

This example of frost This example of frost wedging is from Pikes Peak wedging is from Pikes Peak in Colorado. The weathered in Colorado. The weathered

fragments of rock break fragments of rock break apart from the exposed apart from the exposed rock from freeze-thaw rock from freeze-thaw action and collect as action and collect as

angular blocks of talus angular blocks of talus material. material.

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Temperature ChangesTemperature Changes Daily (diurnal) and seasonal temperature changes affect certain minerals Daily (diurnal) and seasonal temperature changes affect certain minerals

and facilitates the mechanical weathering of bedrock.and facilitates the mechanical weathering of bedrock. Warmer temperatures may cause some minerals to expand, and cooler Warmer temperatures may cause some minerals to expand, and cooler

temperatures cause them to contract.temperatures cause them to contract. This gradual expansion and contraction of mineral grains weakens the rock This gradual expansion and contraction of mineral grains weakens the rock

causing it to break apart into smaller fragments or to fracture. causing it to break apart into smaller fragments or to fracture. This process is more common in desert climates because they experience This process is more common in desert climates because they experience

extreme fluctuations in daily temperature changes.extreme fluctuations in daily temperature changes. Temperature changes are often not the dominant form of weathering, but Temperature changes are often not the dominant form of weathering, but

instead temperature changes tend to accelerate other forms of weathering instead temperature changes tend to accelerate other forms of weathering already occurring.already occurring.

© Copyright 2008 Imperial College London

The rock fragments in the lower The rock fragments in the lower right side of this image have right side of this image have

weathered as a result of extreme weathered as a result of extreme fluctuations in day and night fluctuations in day and night

temperature changes. temperature changes.

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Mechanical Weathering: Salt Mechanical Weathering: Salt

WedgingWedging Salt wedging occurs when salts crystallize out of solution as water Salt wedging occurs when salts crystallize out of solution as water

evaporates. As the salt crystals grow, they apply pressure to the evaporates. As the salt crystals grow, they apply pressure to the surrounding rock weakening it, until it eventually cracks and breaks down, surrounding rock weakening it, until it eventually cracks and breaks down, enabling the salt crystal to continue growing.enabling the salt crystal to continue growing.

Salt wedging is most common in drier climates, such as deserts. Salt wedging is most common in drier climates, such as deserts.

Copyright Copyright © Michael Collier© Michael Collier

These salt crystals were foundThese salt crystals were found growing between rock fractures in growing between rock fractures in

California’s Death Valley. California’s Death Valley.

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Mechanical Weathering: AbrasionMechanical Weathering: Abrasion Abrasion occurs when rocks collide against each Abrasion occurs when rocks collide against each

other while they are transported by water, glacial other while they are transported by water, glacial ice, wind, or gravitational force.ice, wind, or gravitational force.

The constant collision or gravitational falling of the The constant collision or gravitational falling of the rocks causes them to slowly break apart into rocks causes them to slowly break apart into progressively smaller particles. progressively smaller particles.

Flowing water is the primary medium of abrasion Flowing water is the primary medium of abrasion and it produces the ‘rounded’ shape of fluvial and it produces the ‘rounded’ shape of fluvial sediments.sediments.

During abrasion, rocks may also weather the During abrasion, rocks may also weather the bedrock surface they are coming into contact with bedrock surface they are coming into contact with as well as breaking into smaller particles and as well as breaking into smaller particles and eventually individual grains.eventually individual grains.

In addition to the transported rocks being In addition to the transported rocks being weathered by abrasion, the bedrock surface is also weathered by abrasion, the bedrock surface is also experiencing the effects of collision and mechanical experiencing the effects of collision and mechanical weathering. This smoothes the surface of the weathering. This smoothes the surface of the bedrock and can also cause it to break apart.bedrock and can also cause it to break apart.

Photo Source: SCGSPhoto Source: SCGS

Abrasion processes in creek bedsAbrasion processes in creek bedsproduce rounded boulders and produce rounded boulders and

cobbles.cobbles.Over time, abrasion processes will Over time, abrasion processes will eventually break these rocks into eventually break these rocks into

progressively smaller particle sizes, progressively smaller particle sizes, such such

as gravel, sand, silt, and clay.as gravel, sand, silt, and clay.



Types of Chemical WeatheringTypes of Chemical Weathering

Chemical weatheringChemical weathering decomposes, dissolves, decomposes, dissolves, alters, or weakens the rock through chemical alters, or weakens the rock through chemical processes to form residual materials.processes to form residual materials.

CarbonationCarbonationHydrolysisHydrolysisHydrationHydrationOxidationOxidationSolutionSolution

Copyright © Oklahoma UniversityCopyright © Oklahoma University

Stalactite and stalagmite joining together in Stalactite and stalagmite joining together in Onondaga Cave State Park, Missouri. Onondaga Cave State Park, Missouri.



Chemical Weathering: CarbonationChemical Weathering: Carbonation Carbonation is a process by which carbon dioxide and rainwater or Carbonation is a process by which carbon dioxide and rainwater or

moisture in the surrounding environment chemically react to produce moisture in the surrounding environment chemically react to produce carbonic acid, a weak acid, that reacts with carbonate minerals in the rock. carbonic acid, a weak acid, that reacts with carbonate minerals in the rock.

This process simultaneously weakens the rock and removes the chemically This process simultaneously weakens the rock and removes the chemically weathered materials. weathered materials.

Carbonation primarily occurs in wet, moist climates and effects rocks both Carbonation primarily occurs in wet, moist climates and effects rocks both on and beneath the surface.on and beneath the surface.

Carbonation occurs with limestone or dolomite rocks and usually produces Carbonation occurs with limestone or dolomite rocks and usually produces very fine, clayey particles.very fine, clayey particles.

Limestone weathered by Limestone weathered by carbonation processes carbonation processes

Photo source: Wikipedia GNU Free Documentation Photo source: Wikipedia GNU Free Documentation LicenseLicense



Chemical Weathering: HydrolysisChemical Weathering: Hydrolysis Hydrolysis is a chemical reaction between HHydrolysis is a chemical reaction between H++ and OH and OH-- ions in water and the ions in water and the

minerals in the rock. The Hminerals in the rock. The H++ ions in the water react with the minerals to ions in the water react with the minerals to produce weak acids. produce weak acids.

The reaction creates new compounds which tend to be softer and weaker than The reaction creates new compounds which tend to be softer and weaker than the original parent rock material.the original parent rock material.

Hydrolysis can also cause certain minerals to expand, which also facilitates Hydrolysis can also cause certain minerals to expand, which also facilitates mechanical weathering processes.mechanical weathering processes.

Hydrolysis commonly affects igneous rocks because they are composed of Hydrolysis commonly affects igneous rocks because they are composed of silicate minerals, such as quartz and feldspar, which readily combine with silicate minerals, such as quartz and feldspar, which readily combine with water.water.

Hydrolysis may also be accompanied by hydration and oxidation weathering Hydrolysis may also be accompanied by hydration and oxidation weathering processes.processes.

The hydrolysis of feldspars produces kaolinite, which is a clay.The hydrolysis of feldspars produces kaolinite, which is a clay.

Photo Source: Dr. Hugh Mills, Tennessee Technical UniversityPhoto Source: Dr. Hugh Mills, Tennessee Technical University

The weathering rinds shown on this sample The weathering rinds shown on this sample of amphibolite illustrate the effects of of amphibolite illustrate the effects of

hydrolysis weathering on deposited rock hydrolysis weathering on deposited rock fragments. Geologists measure the fragments. Geologists measure the

‘thickness’ of the weathering rinds on in-‘thickness’ of the weathering rinds on in-situ rock fragments to estimate the situ rock fragments to estimate the

relative age of depositional landforms such relative age of depositional landforms such as river terraces or alluvial fans. The as river terraces or alluvial fans. The

thicker the weathering rinds, the older the thicker the weathering rinds, the older the landform. landform.



Chemical Weathering: HydrationChemical Weathering: Hydration Hydration is a process where mineral structure in the rock forms a weak

bond with H20 which causes the mineral grains to expand, creating stress which causes the disintegration of the rock.

Hydration often produces a new mineral compound that is larger than the original compound. The increased size expanse the rock and can lead to decay.

Hydration can also lead to color changes in the weathered rock surface. Once hydration begins, it accelerates other weathering processes and may

also be accompanied by hydrolysis and oxidation. An example of hydrolosis: Anhydrite (CaSO4) can absorb two water

molecules to become gypsum (CaSO4·2H2O). Hydration in granite transforms feldspar minerals to clay and accelerates

the physical weathering of buried or exposed rocks.

Copyright ©Bruce Molnia, USGS

This boulder is surrounded by This boulder is surrounded by saprolitic soils formed by the saprolitic soils formed by the

weathered rock. Hydration processes weathered rock. Hydration processes cause the formation of clays and cause the formation of clays and

contribute to the reddish-tan color of contribute to the reddish-tan color of the saprolite. the saprolite.



Chemical Weathering: OxidationChemical Weathering: Oxidation

Oxidation occurs when oxygen and water react with iron-rich minerals and weaken the structure of the mineral.

During oxidation the minerals in the rock will change colors, taking on a ‘rusty’, reddish-orange appearance.

Similar to other chemical weathering processes, oxidation accelerates rock decay, rendering it more vulnerable to other forms of weathering.

Photo: SCGS

The reddish-orange color of this The reddish-orange color of this sandstone is a result of oxidation sandstone is a result of oxidation processes weathering the rock. processes weathering the rock.



Chemical Weathering: SolutionChemical Weathering: Solution Solution occurs when minerals in rock dissolve directly into water. Solution occurs when minerals in rock dissolve directly into water. Solution most commonly occurs on rocks containing carbonates such as Solution most commonly occurs on rocks containing carbonates such as

limestone, but may also affect rocks with large amount of halite, or rock limestone, but may also affect rocks with large amount of halite, or rock salt.salt.

Solution of large areas of bedrock may cause sinkholes to form, where Solution of large areas of bedrock may cause sinkholes to form, where large areas of the ground subside or collapse forming a depression.large areas of the ground subside or collapse forming a depression.

Copyright Copyright © Larry Fellows, Arizona Geological Survey© Larry Fellows, Arizona Geological Survey

Subsurface dissolution of halite has Subsurface dissolution of halite has caused overlying rocks to collapse caused overlying rocks to collapse

and form crater-like features.and form crater-like features.

Copyright Copyright © Bruce Molina, USGS© Bruce Molina, USGS

This is an example of a This is an example of a limestone solution karst limestone solution karst feature found in Florida's feature found in Florida's Everglades National Park. Everglades National Park.



Biological WeatheringBiological Weathering

Biological weatheringBiological weathering is the disintegration or decay is the disintegration or decay of rocks and minerals caused by chemical or of rocks and minerals caused by chemical or physical agents of organisms.physical agents of organisms.

Organic activity from lichen and algaeOrganic activity from lichen and algaeRock disintegration by plant growthRock disintegration by plant growthBurrowing and tunneling organismsBurrowing and tunneling organismsSecretion of acidsSecretion of acids



Lichen, Algae, and Decaying Lichen, Algae, and Decaying PlantsPlants Organisms such as lichen and algae often live on bare rock and extract Organisms such as lichen and algae often live on bare rock and extract

minerals from the rock by ion-exchange mechanisms.minerals from the rock by ion-exchange mechanisms. This bio-chemical weathering process leaches minerals from the rock This bio-chemical weathering process leaches minerals from the rock

causing it to weaken and breakdown.causing it to weaken and breakdown. The decaying of plant materials can also produce acidic compounds which The decaying of plant materials can also produce acidic compounds which

dissolve the exposed rock.dissolve the exposed rock. The presence of organisms growing, expanding, or moving across the The presence of organisms growing, expanding, or moving across the

surface of the rock also exerts a small amount of abrasion and pressure surface of the rock also exerts a small amount of abrasion and pressure that gradually cause the mechanical weathering of the rock as the that gradually cause the mechanical weathering of the rock as the organisms extract various minerals.organisms extract various minerals.

Photo: SCGSPhoto: SCGS

This is an example of This is an example of biological weathering that is biological weathering that is caused by mosses and lichen caused by mosses and lichen

growing on growing on the face of a rock.the face of a rock.



Plant Roots Plant Roots The most common form of biological weathering is when plant roots The most common form of biological weathering is when plant roots

penetrate into cracks and crevices of rocks and cause the rock to split or penetrate into cracks and crevices of rocks and cause the rock to split or break into smaller particles through mechanical weathering.break into smaller particles through mechanical weathering.

Although, this process is gradual, it can be fairly effective at breaking apart Although, this process is gradual, it can be fairly effective at breaking apart rocks that may already have a pre-existing weaknesses such as fractures, rocks that may already have a pre-existing weaknesses such as fractures, faults, or joints.faults, or joints.

Copyright © Bruce Molnia, Terra PhotographicsCopyright © Bruce Molnia, Terra Photographics

This is an example of a tree This is an example of a tree that is growing between a that is growing between a

crevasse in a rock. The tree crevasse in a rock. The tree is splitting the rock along is splitting the rock along

parallel planes of parallel planes of alignment that are already alignment that are already

weakened by foliation weakened by foliation processes, a form of processes, a form of

mechanical weathering.mechanical weathering.



Organism ActivityOrganism Activity Burrowing, tunneling, and acid-secreting organisms are another form of Burrowing, tunneling, and acid-secreting organisms are another form of

biological weathering that chemically or mechanically contribute to biological weathering that chemically or mechanically contribute to weathering. weathering.

Some animals may burrow or tunnel into rocks or cracks in rocks and cause Some animals may burrow or tunnel into rocks or cracks in rocks and cause the rock to break down and disintegrate. Small animals, worms, termites, the rock to break down and disintegrate. Small animals, worms, termites, and other insects, often contribute to this form of biological weathering.and other insects, often contribute to this form of biological weathering.

Some organisms, such as snails, barnacles, or limpets, attach themselves Some organisms, such as snails, barnacles, or limpets, attach themselves to rocks and secrete acid acids that chemically dissolve the rock surface. to rocks and secrete acid acids that chemically dissolve the rock surface.

Photo: D. KroessigPhoto: D. Kroessig

The periwinkle snails on The periwinkle snails on this rock are secreting this rock are secreting acids that dissolve the acids that dissolve the

rock. This picture is taken rock. This picture is taken from a volcanic shoreline in from a volcanic shoreline in

Hawaii.Hawaii.



Differential WeatheringDifferential Weathering Weathering rates will not only vary depending on the type of weathering Weathering rates will not only vary depending on the type of weathering

process, whether it is mechanical, chemical, or biological, but they will also process, whether it is mechanical, chemical, or biological, but they will also vary depending on the rock material that is being weathered. vary depending on the rock material that is being weathered.

Some rocks are harder than other rocks, and will weather slower than Some rocks are harder than other rocks, and will weather slower than softer rocks. softer rocks.

The differences in rates of weathering due to different types of rocks, The differences in rates of weathering due to different types of rocks, textures, or other characteristics is referred to as differential weathering.textures, or other characteristics is referred to as differential weathering.

Differential weathering processes contribute to the unique formation of Differential weathering processes contribute to the unique formation of many landforms, including pedestals, waterfalls, and monadnocks.many landforms, including pedestals, waterfalls, and monadnocks.

Climate can also produce differential weathering responses for the same Climate can also produce differential weathering responses for the same rock type. For example, limestone weathers more quickly in wet climates rock type. For example, limestone weathers more quickly in wet climates than dry climates. than dry climates. Peachtree Rock’s unique pyramidal

shape is a result of differential weathering associated with the

different sedimentary sandstone rock components. The top portion of the

outcrop consists of hard, coarse-grained sandstone, while the lower

part of the rock consist of a less cohesive, sandstone layer. The lower

portion of the rock has weathered more quickly than the upper portion

ultimately producing its unique pyramidal shape.

2222Image source: SCDNR, Heritage Preserves Table of Contents


ErosionErosion Water erodes rocks and the landscapes by transporting weathered erodes rocks and the landscapes by transporting weathered

materials from their source to another location where they are materials from their source to another location where they are deposited. deposited.

Wind erodes materials by picking them up and temporarily erodes materials by picking them up and temporarily transporting them from their source to another location where transporting them from their source to another location where they are deposited, and either stored or re-mobilized and they are deposited, and either stored or re-mobilized and transported to another location.transported to another location.

Ice erosion occurs when particles are plucked up or incorporated erosion occurs when particles are plucked up or incorporated by moving ice, such as a glaciers, and are transported downhill, or by moving ice, such as a glaciers, and are transported downhill, or when friction between the ice and bedrock erodes materials and when friction between the ice and bedrock erodes materials and then transports them downhill.then transports them downhill.

Gravity facilitates the down slope transportation of loosened, facilitates the down slope transportation of loosened, weathered materials and enables them to move without the aid of weathered materials and enables them to move without the aid of water, wind, or ice. Gravity related erosion is a major component water, wind, or ice. Gravity related erosion is a major component of mass-wasting events.of mass-wasting events.

Copyright ©Marli Miller, University of Oregon

This basin and range landscape is This basin and range landscape is influenced by several erosional influenced by several erosional

processes. The mountains in the processes. The mountains in the background are dissected by fluvial background are dissected by fluvial erosion (water) and the sandstorm erosion (water) and the sandstorm

in the valley is a form of aeolian in the valley is a form of aeolian (wind) erosion. The mountains may (wind) erosion. The mountains may

contain numerous rocks falls or contain numerous rocks falls or landslides a form of gravity related landslides a form of gravity related

mass-wasting erosion. mass-wasting erosion. 2323

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Erosion: Water (Fluvial)Erosion: Water (Fluvial) Water erodes rocks and shapes the landscapes by removing and Water erodes rocks and shapes the landscapes by removing and

transporting weathered materials from their source to another location transporting weathered materials from their source to another location where they are deposited and either stored or transported to another where they are deposited and either stored or transported to another location.location.

Fluvial erosion is often broken into 3 distinct categories: Fluvial erosion is often broken into 3 distinct categories: rain-splash erosion, sheet erosion, and and rill/gully erosion.

Rain splash erosion occurs when the impact of a rain drop loosens and occurs when the impact of a rain drop loosens and mobilizes particles.mobilizes particles.

Sheet erosion is a process where particles loosened buy rain-splash erosion are is a process where particles loosened buy rain-splash erosion are transported by runoff water down the slope of a surface. transported by runoff water down the slope of a surface.

Rill erosion occurs when water concentrates during sheet erosion and erodes occurs when water concentrates during sheet erosion and erodes small rills or gullys into the surface that channel flow down slope. small rills or gullys into the surface that channel flow down slope.

Fluvial erosion can occur during rainfall events, from melt-water runoff, or Fluvial erosion can occur during rainfall events, from melt-water runoff, or ground water percolation. Materials being eroded and transported are ground water percolation. Materials being eroded and transported are either suspended in the water, bounced by saltation, or rolled along the either suspended in the water, bounced by saltation, or rolled along the ground by traction depending on a variety of conditions. ground by traction depending on a variety of conditions.

The accumulation of fluvial erosion and associated processes over a large The accumulation of fluvial erosion and associated processes over a large area forms pathways for surface and groundwater flow and carves v-shaped area forms pathways for surface and groundwater flow and carves v-shaped river valleys that continue to erode, transport, and deposit weathered river valleys that continue to erode, transport, and deposit weathered sediments across the landscape. sediments across the landscape.

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This drawing on the left This drawing on the left illustrates rain-splash illustrates rain-splash impact on the soil and impact on the soil and

the erosion of individual the erosion of individual grains of sediment. The grains of sediment. The

image on the right shows image on the right shows the landscape scale the landscape scale

effects of fluvial erosion. effects of fluvial erosion. www.montcalm.org Copyright ©Marli

Miller


http://www.montcalm.org/planningeduc0042.asp

Erosion: Wind (Aeolian)Erosion: Wind (Aeolian) Wind erodes weathered rocks by picking them up and temporarily Wind erodes weathered rocks by picking them up and temporarily

transporting them from their source to another location where they are transporting them from their source to another location where they are deposited, and either stored or re-mobilized and transported to another deposited, and either stored or re-mobilized and transported to another locationlocation

Erosion by wind is divided into two different categories: Erosion by wind is divided into two different categories: Deflation and and Abrasion

Deflation is the movement or transport of particles through the air or along the is the movement or transport of particles through the air or along the groundground

Abrasion is theis the process that occurs when wind-transported particles sculpt process that occurs when wind-transported particles sculpt features in the landscape through a “sand-blasting” like process features in the landscape through a “sand-blasting” like process

Aeolian erosion and deposition processes create a diversity of landforms Aeolian erosion and deposition processes create a diversity of landforms including sand dunes, loess deposits, and yardangs.including sand dunes, loess deposits, and yardangs.


Courtesy Modis, Nasa

This satellite image captured a This satellite image captured a regional dust storm transporting regional dust storm transporting

aeolian sediments from Sudan and aeolian sediments from Sudan and Africa over the Red Sea. In arid, Africa over the Red Sea. In arid,

desert climates wind erosion is very desert climates wind erosion is very common and can transport common and can transport

sediments 100’s of miles before sediments 100’s of miles before they are deposited. they are deposited.


Erosion: Ice (Periglacial and Erosion: Ice (Periglacial and Glacial)Glacial)

Ice erosion occurs in combination with periglacial and glacial processes Ice erosion occurs in combination with periglacial and glacial processes Glacial erosion occurs when particles are incorporated into the glacial ice Glacial erosion occurs when particles are incorporated into the glacial ice

through a process referred to as plucking, and they are transported through a process referred to as plucking, and they are transported downslope within the glacier.downslope within the glacier.

The friction and abrasion of the ice and rock moving across the bedrock, The friction and abrasion of the ice and rock moving across the bedrock, erodes the surface of the bedrock and often leaves scrapes, grooves, striae, erodes the surface of the bedrock and often leaves scrapes, grooves, striae, or polished rock surfaces. or polished rock surfaces.

The cumulative effects of glacial erosion on a mountainous landscape can The cumulative effects of glacial erosion on a mountainous landscape can produce distinct u-shaped valleys which are a common glacial landform. produce distinct u-shaped valleys which are a common glacial landform.

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Glacial erosion of this Glacial erosion of this landscape has carved several landscape has carved several distinct landforms, such as distinct landforms, such as the glacial u-shaped valleys the glacial u-shaped valleys and the arêtes, which form and the arêtes, which form the ridges between the u-the ridges between the u-

shape valleys. shape valleys.

Copyright ©Bruce Molnia USGSTable of Contents


Erosion: GravityErosion: Gravity Gravity facilitates the down slope transportation of loosened, weathered Gravity facilitates the down slope transportation of loosened, weathered

materials and enables them to move without the aid of water, wind, or ice. materials and enables them to move without the aid of water, wind, or ice. However, these agents can act as catalysts for gravity related erosion.However, these agents can act as catalysts for gravity related erosion.

Movements by gravity may be very slow or very abrupt.Movements by gravity may be very slow or very abrupt. Gravity related erosion can be coherent or incoherent. Coherent refers to the Gravity related erosion can be coherent or incoherent. Coherent refers to the

erosion of a consolidated mass of materials that erode or move as a single erosion of a consolidated mass of materials that erode or move as a single unit, incoherent refers to the erosion or movement of a mass of unit, incoherent refers to the erosion or movement of a mass of unconsolidated individual fragments of materials.unconsolidated individual fragments of materials.

Unconsolidated materials tend to stabilize near an angle of 35Unconsolidated materials tend to stabilize near an angle of 35° (referred to ° (referred to as the angle of repose) however this balance is easily disrupted by changes as the angle of repose) however this balance is easily disrupted by changes in environmental conditions, addition of weathered materials, and or other in environmental conditions, addition of weathered materials, and or other adjustments that may cause mass wasting. adjustments that may cause mass wasting.


The rock fragments and The rock fragments and sediments accumulated below sediments accumulated below this cliff were eroded by the this cliff were eroded by the

force of gravity and were force of gravity and were deposited as talus scree at the deposited as talus scree at the

base of the cliff. When the base of the cliff. When the slope at the base of the cliff slope at the base of the cliff

becomes too steep, and becomes too steep, and exceeds the angle of repose, exceeds the angle of repose,

the unconsoldated particles will the unconsoldated particles will again be eroded and again be eroded and

transported down slope by transported down slope by gravity. gravity.

Photo: wikimedia commons


Mass WastingMass Wasting

Rock FallsRock Falls LandslidesLandslides Debris / Mud FlowsDebris / Mud Flows SlumpsSlumps CreepCreep

Photo source: SCGSPhoto source: SCGS

LandslideLandslide

Copyright ©John BallardCopyright ©John Ballard

Rock FallRock Fall


Mass wasting is a rapid form of erosion that works primarily under the influence of gravity in combination with other erosional agents. Mass wasting occurs very quickly and can result in either small or large scale changes to the landscape depending on the type of event.


Rock FallsRock Falls Rock falls occur when rocks become dislodged, because their change in Rock falls occur when rocks become dislodged, because their change in

potential energy becomes to great to maintain, and the potential energy potential energy becomes to great to maintain, and the potential energy becomes kinetic energy which causes the rock fragment to fall, restoring becomes kinetic energy which causes the rock fragment to fall, restoring equilibrium. As a result the rocks fall, roll, or bounce downhill. equilibrium. As a result the rocks fall, roll, or bounce downhill.

The rocks may be loosened by a recent rainfall or snow melt-water event that The rocks may be loosened by a recent rainfall or snow melt-water event that facilitates the movement of the rock before they fall from the force of gravity.facilitates the movement of the rock before they fall from the force of gravity.

Rock falls often form piles of loose rock below their source and are Rock falls often form piles of loose rock below their source and are sometimes referred to as talus or scree.sometimes referred to as talus or scree.

Large volumes of talus may form a talus slope, talus apron, or talus cone Large volumes of talus may form a talus slope, talus apron, or talus cone depending on its shape. Talus tends to stabilize near an angle of 35° depending on its shape. Talus tends to stabilize near an angle of 35° (referred to as the angle of repose), or the steepest angle maintained before (referred to as the angle of repose), or the steepest angle maintained before changes in energy lead to gravitational erosion. This balance is easily changes in energy lead to gravitational erosion. This balance is easily disrupted by changes in environmental conditions, addition of weathered disrupted by changes in environmental conditions, addition of weathered materials, or other factors that lead to mass wasting. materials, or other factors that lead to mass wasting.

Photo courtesy of SCGSPhoto courtesy of SCGS

Fragments are breaking off from Fragments are breaking off from this rock exposure and collecting this rock exposure and collecting

down-slope from their source. The down-slope from their source. The fragments of fallen rock are fragments of fallen rock are

angular and include a variety of angular and include a variety of different sizes. The tree growing different sizes. The tree growing above this boulder may also be above this boulder may also be contributing through biological contributing through biological weathering where the roots are weathering where the roots are

penetrating into the cracks in the penetrating into the cracks in the rock.rock.



LandslidesLandslides Landslides are mass-wasting events where Landslides are mass-wasting events where

large amounts of weathered rock material slide large amounts of weathered rock material slide down a hillslope or mountain side primarily by down a hillslope or mountain side primarily by gravity related erosion.gravity related erosion.

Landslides occur very quickly and move with Landslides occur very quickly and move with incredible speed and destruction, often incredible speed and destruction, often removing or covering everything in their path. removing or covering everything in their path.

Nearly all landslides are triggered by an Nearly all landslides are triggered by an earthquake, or lubricant agent such as rainfall, earthquake, or lubricant agent such as rainfall, or a snow or ice melt-water event.or a snow or ice melt-water event.

During intensive rainfall, soil and weathered During intensive rainfall, soil and weathered rock material become unstable and loosened rock material become unstable and loosened from the saturated conditions that separate the from the saturated conditions that separate the individual grains and other material fragments. individual grains and other material fragments. The increased fluid pressures coupled with the The increased fluid pressures coupled with the loosened materials succumbs to gravity related loosened materials succumbs to gravity related erosion and the weathered materials plunge erosion and the weathered materials plunge downhill as a powerful landslide.downhill as a powerful landslide.

Landslides are a natural hazard that can cause Landslides are a natural hazard that can cause serious damage to people and other obstacles serious damage to people and other obstacles in their path. Many earth scientists study in their path. Many earth scientists study landslides in order to predict their occurrence landslides in order to predict their occurrence and prevent negative impacts to humans and and prevent negative impacts to humans and infrastructure. infrastructure.

This landslide event occurred in This landslide event occurred in Jones Gap State Park in the Jones Gap State Park in the Mountain Bridge Wilderness Mountain Bridge Wilderness

Area of South Carolina. Area of South Carolina. Boulders, trees, soil, and other Boulders, trees, soil, and other

weathered material tumbled weathered material tumbled down this hill-slope after 8’’ of down this hill-slope after 8’’ of

heavy rain fell over 2-days. heavy rain fell over 2-days.

Photo source: Photo source: SCGSSCGS 3030

Table of Contents


Debris and Mud FlowsDebris and Mud Flows Debris and mudflows are mass-wasting events that form when heavy Debris and mudflows are mass-wasting events that form when heavy

rainfalls produce large amounts of runoff that transport eroded soils, rainfalls produce large amounts of runoff that transport eroded soils, sediments, and plant debris down slope where the flows eventually sediments, and plant debris down slope where the flows eventually spreads out across valley bottoms.spreads out across valley bottoms.

Sometimes the debris and mudflows follow existing drainage paths and Sometimes the debris and mudflows follow existing drainage paths and other times they carve out new paths as they flow downhillother times they carve out new paths as they flow downhill

Debris and mudflows can carry particles of a range of sizes from clays Debris and mudflows can carry particles of a range of sizes from clays (mud) to large debris and boulders; however, debris flows consists (mud) to large debris and boulders; however, debris flows consists primarily of coarse-grained materials and mudflows consist primarily of primarily of coarse-grained materials and mudflows consist primarily of fine-grained materials. fine-grained materials.

The consistency of a debris or mudflow is representative of a thick, muddy The consistency of a debris or mudflow is representative of a thick, muddy sludge carrying rocks, twigs, branches, trees, and other available debrissludge carrying rocks, twigs, branches, trees, and other available debris

Debris flows are natural hazards that pose a threat to communities in their Debris flows are natural hazards that pose a threat to communities in their pathpath

This debris flow flooded and This debris flow flooded and destroyed several homes as it destroyed several homes as it

carried, mud, trees, and boulders carried, mud, trees, and boulders through a valley in Colorado’s through a valley in Colorado’s

Rocky Mountain Range. Rocky Mountain Range.

Copyright©Marli Miller, University of OregonCopyright©Marli Miller, University of Oregon 3131Table of Contents


SlumpSlump Slumps are a fairly common form of mass wasting where the rock or soil Slumps are a fairly common form of mass wasting where the rock or soil

collapses, breaks off from the hill slope, rotates slightly, and slumps collapses, breaks off from the hill slope, rotates slightly, and slumps downhill.downhill.

If the slump occurs as a large consolidated mass of materials it is If the slump occurs as a large consolidated mass of materials it is considered coherent, if it occurs as a mass of unconsolidated materials or considered coherent, if it occurs as a mass of unconsolidated materials or sediments it is referred to as incoherent.sediments it is referred to as incoherent.

Slumping can cause damage to houses, roads, and other infrastructure.Slumping can cause damage to houses, roads, and other infrastructure.

This slump failure in California This slump failure in California poses a threat to homes poses a threat to homes

developed along the edge of the developed along the edge of the cliff.cliff.

Copyright ©Bruce Molnia, Terra PhotographicsCopyright ©Bruce Molnia, Terra Photographics

The asphalt The asphalt from the road from the road surface makes surface makes it easy to see it easy to see

the soil the soil displacement displacement

from this from this slump.slump.



CreepCreep Creep is the slowest mass-wasting process and involves a very gradual Creep is the slowest mass-wasting process and involves a very gradual

downhill movement of soil, bedrock, and weathered rock fragments. downhill movement of soil, bedrock, and weathered rock fragments. Usually, the entire slope is slowly creeping downhill as a complete unit. Usually, the entire slope is slowly creeping downhill as a complete unit. Creep processes occur to some degree on nearly every hillslope because of Creep processes occur to some degree on nearly every hillslope because of

gravity. gravity. Creep is evident by bent or extended tree trunks that are adjusting to the Creep is evident by bent or extended tree trunks that are adjusting to the

slow movement of the soil, regolith, and weathered material they are slow movement of the soil, regolith, and weathered material they are rooted into.rooted into.

Freeze-thaw cycles and saturated conditions may accelerate creep Freeze-thaw cycles and saturated conditions may accelerate creep processes but usually only for a short time-periodprocesses but usually only for a short time-period

Solifluction is a certain form of creep where frozen tundra soils thaw out Solifluction is a certain form of creep where frozen tundra soils thaw out and gently ‘flow’ or sag downslope and gently ‘flow’ or sag downslope

The bent, leaning trees in this The bent, leaning trees in this image are an indication of soil image are an indication of soil

creep. The soil beneath the tree creep. The soil beneath the tree roots is slowing creeping roots is slowing creeping

downhill, as a result the tree downhill, as a result the tree trunks curve upslope in order for trunks curve upslope in order for

the trees to remain upright.the trees to remain upright.

Copyright © Marli Miller, University of OregonCopyright © Marli Miller, University of Oregon 3333Table of Contents


DepositionDeposition Deposition is a constructive process that lays down or places weathered Deposition is a constructive process that lays down or places weathered

and eroded materials in a location that is different from their source. and eroded materials in a location that is different from their source. Deposition is not specific to a single weathering, erosion, or mass wasting Deposition is not specific to a single weathering, erosion, or mass wasting

event, but is applied to any consolidated or unconsolidated materials that event, but is applied to any consolidated or unconsolidated materials that have accumulated as a result of some natural process or agent. Deposits have accumulated as a result of some natural process or agent. Deposits can result from mechanical, chemical, or biological weathering, and water, can result from mechanical, chemical, or biological weathering, and water, wind, ice, or gravity-related erosional processes. wind, ice, or gravity-related erosional processes.

The accumulation of deposited materials alters the landscapes and builds The accumulation of deposited materials alters the landscapes and builds various landform features. For example, floodplains are large depositional various landform features. For example, floodplains are large depositional landforms built by the accumulation of fluvial deposits, and sand dunes are landforms built by the accumulation of fluvial deposits, and sand dunes are depositional landforms built by wind-related processes. depositional landforms built by wind-related processes.

Colluvium is the term used Colluvium is the term used to describe weathered and to describe weathered and

eroded rocks, soil, and eroded rocks, soil, and sediments deposited at the sediments deposited at the base of a hill slope or cliff base of a hill slope or cliff by the force of gravity and by the force of gravity and mass wasting. Alluvium is mass wasting. Alluvium is

a term used to refer a term used to refer materials deposited by materials deposited by

running water. The talus running water. The talus slope on the left is slope on the left is

colluvium and the alluvial colluvium and the alluvial fan on the right is fan on the right is

alluvium. alluvium. 3434Table of Contents

Copyright©John Ballard

Copyright© Marli Miller


South Carolina Science Academic South Carolina Science Academic Standards: Grade 3Standards: Grade 3


1) Earth’s Materials and Changes: Standard 3-3: The student will demonstrate an understanding of Earth’s composition and the changes that occur to the features of Earth’s surface.

Indicators:3-3.8: Illustrate changes in Earth’s surface that are due to slow processes (including weathering, erosion, and deposition) and changes that are due to rapid processes (including landslides, volcanic eruptions, floods, and earthquakes).

South Carolina Science Academic South Carolina Science Academic Standards: Grade 5Standards: Grade 5


1) Lanforms and Ocean: Standard 5-3: The student will demonstrate an understanding of features, processes, and changes in Earth’s lands and oceans.

Indicators:5-3.1: Explain how natural processes (including weathering, erosion, deposition, landslides, volcanic eruptions, earthquakes, and floods) affect Earth’s oceans and land in constructive and destructive ways.

Resources and ReferencesResources and References

AGI, 1972, Glossary of Geology: American Geological Institute, Washington, D.C.

Christopherson, R. W., 2004, Elemental Geosystems (4th ed.): Upper Saddle River, New Jersey, Prentice Hall.

Lutgens, F. K., and Tarbuck. E. J., 2003, Essentials of Geology (8th ed.): Upper Saddle River, New Jersey, Prentice Hall.


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