weathering, erosion and mass wasting

(c) Vicki Drake, 2010(c) Vicki Drake, 2010 11

WEATHERING, EROSION WEATHERING, EROSION AND MASS WASTINGAND MASS WASTING


What is Weathering?What is Weathering? Weathering is the combined actions of all Weathering is the combined actions of all

processes that cause rock to disintegrate processes that cause rock to disintegrate physically or decompose chemically. physically or decompose chemically.

Weathering processes include ‘physical’ Weathering processes include ‘physical’ weathering or ‘chemical’ weatheringweathering or ‘chemical’ weathering– Physical Weathering – breaks rocks down into Physical Weathering – breaks rocks down into

smaller and smaller piecessmaller and smaller pieces– Chemical Weathering – completely alters Chemical Weathering – completely alters

minerals in rocks; creates new mineralsminerals in rocks; creates new minerals


Weathering FactorsWeathering Factors Factors that affect weathering include:Factors that affect weathering include:

– Mineralogy of parent rockMineralogy of parent rock– Mafic minerals least resistant to weatheringMafic minerals least resistant to weathering– Felsic minerals more resistant to weatheringFelsic minerals more resistant to weathering

– ClimateClimate Humid climates = more chemical weatheringHumid climates = more chemical weathering Dry climates = more physical (mechanical) weatheringDry climates = more physical (mechanical) weathering

– TimeTime Longer the exposure time, the greater the weathering Longer the exposure time, the greater the weathering

opportunityopportunity

– Number of fissures or openingsNumber of fissures or openings More joints, cracks, and openings allow for greater More joints, cracks, and openings allow for greater

weathering processes to occurweathering processes to occur

– Degree of slopeDegree of slope Steeper slopes encourage greater weathering of exposed Steeper slopes encourage greater weathering of exposed

rocks rocks


..Why and Where Does Weathering Why and Where Does Weathering

Occur?Occur? Weathering occurs at the Earth’s Weathering occurs at the Earth’s

surface as rock materials are surface as rock materials are exposed to the environment.exposed to the environment.

Weathering is possible because all Weathering is possible because all rock materials – no matter how ‘solid’ rock materials – no matter how ‘solid’ - have openings (pore spaces) that - have openings (pore spaces) that allow air, water and other materials allow air, water and other materials to do their work.to do their work.


PHYSICAL (MECHANICAL) PHYSICAL (MECHANICAL) WEATHERINGWEATHERING

Physical Weathering does not change Physical Weathering does not change the basic mineralogy of rock the basic mineralogy of rock – rocks are disintegrated into smaller and rocks are disintegrated into smaller and

smaller pieces, ready for transportsmaller pieces, ready for transport Key ingredient in physical Key ingredient in physical

weathering: waterweathering: water


TYPES OF PHYSICAL TYPES OF PHYSICAL WEATHERINGWEATHERING

Frost (Ice) ActionFrost (Ice) Action: the role of water in : the role of water in weathering when it freezesweathering when it freezes– Frost shattering (ice wedging)Frost shattering (ice wedging)– Frost heaving (ice heaving)Frost heaving (ice heaving)

Stone polygons/rings in high latitude tundraStone polygons/rings in high latitude tundra PingosPingos

Salt Crystal GrowthSalt Crystal Growth Unloading and ExfoliationUnloading and Exfoliation BioturbationBioturbation

– VegetationVegetation– AnimalAnimal


FROST ACTIONFROST ACTION

Frost Action is the repeated growth Frost Action is the repeated growth and melting of ice crystals in pore and melting of ice crystals in pore spaces of soil and within rock spaces of soil and within rock fractures.fractures.


FROST SHATTERING/ICE FROST SHATTERING/ICE WEDGINGWEDGING

This type of physical weathering This type of physical weathering occurs at high altitudes where there occurs at high altitudes where there are definitive cycles of summer and are definitive cycles of summer and winter.winter.

Granites tend to be the most Granites tend to be the most susceptible to this type of weatheringsusceptible to this type of weathering– Most high altitude mountains are Most high altitude mountains are

graniticgranitic



During a thaw cycle (summer, for During a thaw cycle (summer, for instance), water from groundwater or instance), water from groundwater or precipitation finds its way into the fissures precipitation finds its way into the fissures of rocks. of rocks.

In winter, the water freezes and expands In winter, the water freezes and expands by up to 9% in volume pushing the fissure by up to 9% in volume pushing the fissure apart even further.apart even further.

Over many freeze-thaw cycles, rock will Over many freeze-thaw cycles, rock will break into smaller pieces.break into smaller pieces.


Frost Shattering/Ice WedgingFrost Shattering/Ice Wedging


FROST/ICE HEAVINGFROST/ICE HEAVING This type of physical weathering This type of physical weathering

occurs in high latitude regions of the occurs in high latitude regions of the ‘arctic tundra’ ‘arctic tundra’

Tundra are the extremely high Tundra are the extremely high latitude vast open spaces, covered latitude vast open spaces, covered with low-growing grasses and sparse with low-growing grasses and sparse vegetationvegetation..– Some parts of tundra are more ‘bog-like’Some parts of tundra are more ‘bog-like’– Underlain by permanently frozen soils at depth Underlain by permanently frozen soils at depth

- - permafrostpermafrost – Only upper layers thaw during brief weeks of Only upper layers thaw during brief weeks of

‘summer’. ‘summer’.


MAP OF TUNDRA LOCATIONSMAP OF TUNDRA LOCATIONS


Tundra in summer

Tundra in winter


PERMAFROSTPERMAFROST Permafrost is permanently frozen soil, Permafrost is permanently frozen soil,

sediment, or rock. sediment, or rock. Permafrost has a number of different Permafrost has a number of different

layers, of which frozen ground is just layers, of which frozen ground is just one portionone portion

The 'active layer' is ground that is The 'active layer' is ground that is seasonally frozen, typically lying above seasonally frozen, typically lying above the perennially frozen permafrost layer. the perennially frozen permafrost layer. – This is the layer involved with ‘frost This is the layer involved with ‘frost

heaving’heaving’


PERMAFROSTPERMAFROST

The Active layer goes through repeated cycles of freezing and thawing

Frost heaving occurs in the ‘active’ layer


HOW DOES ICE HEAVING HOW DOES ICE HEAVING WORK?WORK?

Summer thaw of upper ‘active’ layer Summer thaw of upper ‘active’ layer allows water to migrate down allows water to migrate down through soil layers under gravitythrough soil layers under gravity

Water ‘pools’ against the more Water ‘pools’ against the more permanently frozen soil layerspermanently frozen soil layers

Winter freeze and water expands Winter freeze and water expands vertically, lifting up overlying soil vertically, lifting up overlying soil layerslayers


ICE/FROST HEAVINGICE/FROST HEAVING


RESULTS OF ICE HEAVINGRESULTS OF ICE HEAVING

As the water freezes, it expands vertically, pushing up the overlying layers

Roads can be affected by ice heaving by warping the surface


FROST HEAVING: PATTERNED FROST HEAVING: PATTERNED GROUND AND STONE RINGSGROUND AND STONE RINGS

Under the right conditions over hundreds of years, stone and soil organize themselves into patterns, through cycles of freezing and thawing.

The frost heaving activity found in the tundra can produce small hills with center depressions (up to 18 inches tall and 3-4 feet across)


Patterned Ground: Stone PolygonsPatterned Ground: Stone Polygons


PINGOSPINGOS PingosPingos are ice-cored hills forming in the are ice-cored hills forming in the

tundratundra

In time, the expanding ice forms an isolated In time, the expanding ice forms an isolated massmass– its volume increases and it pushes up its volume increases and it pushes up

the overlying tundrathe overlying tundra Pingos grow at a rate of approximately one-Pingos grow at a rate of approximately one-

half inch per yearhalf inch per year The tallest pingo in the world (in the The tallest pingo in the world (in the

western Arctic) is 16 stories (192 feet) high.western Arctic) is 16 stories (192 feet) high.


PINGOSPINGOS

PINGO IN NW ALASKA

Salt Crystal ActionSalt Crystal Action Similar to ice-crystal growth – salt Similar to ice-crystal growth – salt

crystals grow insteadcrystals grow instead Susceptible rocks:Susceptible rocks:

– Sandstones in dry and arid regionsSandstones in dry and arid regions Process:Process:

– Groundwater moving down under Groundwater moving down under gravity through permeable gravity through permeable sandstone, naturally high in salts.sandstone, naturally high in salts.

– Water hits an impermeable layer Water hits an impermeable layer (shale, for instance)(shale, for instance)

– Water flows along impermeable Water flows along impermeable shale to an openingshale to an opening

– Water exits rock leaving salt Water exits rock leaving salt crystals behind.crystals behind.

– Salt crystals grow at base of cliff, Salt crystals grow at base of cliff, producing niches (caves)producing niches (caves)

– Base of cliff wears away, rest of Base of cliff wears away, rest of cliff collapses and process begins cliff collapses and process begins againagain


WEATHERED SANDSTONE


Cliff DwellersCliff Dwellers


UNLOADING AND EXFOLIATIONUNLOADING AND EXFOLIATION

Large sections of granitic rock, formed at Large sections of granitic rock, formed at great depth under pressure, brought to great depth under pressure, brought to surface through plate tectonics.surface through plate tectonics.

At the molecular level, the granite At the molecular level, the granite expands in lower pressure environmentexpands in lower pressure environment

Develops fractures in form of thick shells Develops fractures in form of thick shells that peel away from rockthat peel away from rock

Forms rounded features: domes, for Forms rounded features: domes, for instanceinstance


EXFOLIATIONEXFOLIATION


OTHER PHYSICAL WEATHERINGOTHER PHYSICAL WEATHERING

Surface Heating and CoolingSurface Heating and Cooling– Expansion and contraction of rock over Expansion and contraction of rock over

timetime– Fire fracturingFire fracturing

BioturbationBioturbation– Plant rootsPlant roots– Animal burrowingAnimal burrowing


BIOTURBATION

Roots

Fire

Burrowing animals


CHEMICAL WEATHERINGCHEMICAL WEATHERING

Chemical weathering alters the Chemical weathering alters the minerals of rocks – in some cases, minerals of rocks – in some cases, the minerals are dissolved.the minerals are dissolved.

Types of Chemical WeatheringTypes of Chemical Weathering– HydrolysisHydrolysis– OxidationOxidation– Dissolution: Carbonic Acid ActionDissolution: Carbonic Acid Action


HydrolysisHydrolysis The addition of water at the The addition of water at the

molecular level to silicates.molecular level to silicates. Creates a grain-by-grain breakup of Creates a grain-by-grain breakup of

the minerals in Granite into a clay the minerals in Granite into a clay called called KaoliniteKaolinite– Kaolinite used in manufacturing of spark Kaolinite used in manufacturing of spark

plugs and ceramic casings for lights.plugs and ceramic casings for lights.


OxidationOxidation The addition of oxygen molecules (a The addition of oxygen molecules (a

hydroxyl radical) to metallic minerals hydroxyl radical) to metallic minerals (such as iron) (think: RUST)(such as iron) (think: RUST)

Results in decay of igneous and Results in decay of igneous and metamorphic rocks down to 100 metamorphic rocks down to 100 meters or more in tropical areasmeters or more in tropical areas


Dissolution: Carbonic Acid ActionDissolution: Carbonic Acid Action

The mixing of COThe mixing of CO22 and water creates and water creates carbonic acid – a weak acid carbonic acid – a weak acid

Carbonic acid attacks limestones and Carbonic acid attacks limestones and marbles: rocks composed of calcium marbles: rocks composed of calcium carbonate (CaCOcarbonate (CaCO33))

In regions underlain by limestone, In regions underlain by limestone, removal of CaCOremoval of CaCO3 3 results in results in development of karst topographydevelopment of karst topography


Karst TopographyKarst Topography

Regions with limestone bedrock being Regions with limestone bedrock being weathered out.weathered out.

Results in landforms such as caverns, Results in landforms such as caverns, sinkholes, disappearing streams, and low sinkholes, disappearing streams, and low elevation. elevation.

Karst is a German name for an unusual Karst is a German name for an unusual and distinct limestone terrain in Slovenia, and distinct limestone terrain in Slovenia, called Kras.called Kras.


Karst TopographyKarst Topography


EROSION AND MASS WASTINGEROSION AND MASS WASTING

Erosion: Movement of Erosion: Movement of weathered rock over long weathered rock over long distances by water or wind.distances by water or wind.

Mass Wasting: Downslope Mass Wasting: Downslope movement of weathered rock movement of weathered rock over short distances due to over short distances due to gravitygravity


MASS WASTINGMASS WASTING

Main force moving weathered Main force moving weathered materials down slope is gravity.materials down slope is gravity.

Factors that control mass wasting:Factors that control mass wasting:– Steepness of slopeSteepness of slope– Water content of materialsWater content of materials– Presence (or absence) of native Presence (or absence) of native

vegetationvegetation– Human activitiesHuman activities


SLOPE STABILITY: STEEPNESS

W = Weight of total mass of earth material (at center of mass).D = Vector component of W parallel to potential movement.N = Vector component of W normal to slip plane.


SLOPE STABILITY: WATERSLOPE STABILITY: WATER


SLOPE STABILITY: VEGETATIONSLOPE STABILITY: VEGETATION

Native vegetation (such as chaparral) tend Native vegetation (such as chaparral) tend to grow on steep slopes.to grow on steep slopes.

Root structures act as binders and Root structures act as binders and stabilizers of loose unconsolidated stabilizers of loose unconsolidated materials.materials.

Removal of native vegetation through fire Removal of native vegetation through fire or clearing reduce stability of weathered or clearing reduce stability of weathered materials on a slope.materials on a slope.

Vegetation’s role in slope stability:(A, B) Roots support and stabilize soils near surface and at depthC) Upslope soils stabilized by stems and roots close to surface


SLOPE STABILITY: HUMAN SLOPE STABILITY: HUMAN ACTIVITIESACTIVITIES


SLOPE STABILITY: MIININGSLOPE STABILITY: MIININGThe Frank Slide: rock avalanche and is composed of limestone blocks mainly.

At 4:30 am on April 29, 1903, the face of Turtle Mountain, Alberta, Canada, collapsed onto the coal-mining town of Frank, killing at least 70 people.

This landslide has a volume of 30 million cubic meters, and an equivalent weight of 90 million tons


TYPES OF MASS WASTINGTYPES OF MASS WASTING Rock fallRock fall

– Talus slope developmentTalus slope developmentAngle of ReposeAngle of Repose

– Bedrock failureBedrock failure SlidesSlides

– Material remains coherent and moves along Material remains coherent and moves along defined surface: joint, fracture, bedding planesdefined surface: joint, fracture, bedding planes

SlumpsSlumps– Downward rotation of rock/regolith along concave-Downward rotation of rock/regolith along concave-

upward curved surfaceupward curved surface FlowsFlows

– Materials Materials flowflow down slope – mixture of water, rock down slope – mixture of water, rock and other materials (slow to fast movement)and other materials (slow to fast movement)

Slurry: Lahar, Mud Flow, Debris Flow, Slurry: Lahar, Mud Flow, Debris Flow, SolifluctionSolifluction

Granular: Debris avalanche, Earth Flow, Soil Granular: Debris avalanche, Earth Flow, Soil CreepCreep


ROCK FALLSROCK FALLS

Fastest form of mass wasting

Hundreds of tons of rock free-falling to surface

Granitic rock failure


TALUS SLOPESTALUS SLOPES The pile of rocks that accumulates at the base of The pile of rocks that accumulates at the base of

a cliff, chute, or slope. a cliff, chute, or slope. Movements occur whenever the talus slope Movements occur whenever the talus slope

exceeds the critical angle: “angle of repose”exceeds the critical angle: “angle of repose”– ‘‘angle of repose’ is the steepest angle unconsolidated angle of repose’ is the steepest angle unconsolidated

material may remain stablematerial may remain stable The exact angle at which failure takes place The exact angle at which failure takes place

depends upon the materials, rock size, and depends upon the materials, rock size, and moisture content moisture content

Dry homogenous materials in a pile experience Dry homogenous materials in a pile experience slope failure when the angle of repose (the slope failure when the angle of repose (the resting slope angle) exceeds 33–37° resting slope angle) exceeds 33–37°


TALUS SLOPESTALUS SLOPES

Talus (loose, weathered bedrock) falls to base of mountain building up a ramp that is very unstable

TALUS SLOPES AND EXFOLIATION


SLIDES: ROCK AND DEBRISSLIDES: ROCK AND DEBRIS


PORTUGUESE BENDPORTUGUESE BEND Landslides have been active in this region of the Palos Verdes Landslides have been active in this region of the Palos Verdes

Peninsula for thousands of years beginning in the Holocene Peninsula for thousands of years beginning in the Holocene

The 1956 landslide has been attributed to human activities.The 1956 landslide has been attributed to human activities.– Human activities introduced ground water beneath the Human activities introduced ground water beneath the

homes, lubricating a layer of bentonite clay formed by the homes, lubricating a layer of bentonite clay formed by the subsurface weathering of volcanic rock called tuff.subsurface weathering of volcanic rock called tuff.

Landslide encompassed an area of approximately 270 acres Landslide encompassed an area of approximately 270 acres

and involved over 160 homes. and involved over 160 homes.

Rates of slippage have varied, initially moving between 2 and Rates of slippage have varied, initially moving between 2 and 12 cm/day for the first two years, and diminishing to less than 1 12 cm/day for the first two years, and diminishing to less than 1 cm/day during the next four years. cm/day during the next four years.

The slide mass has continued to move for over 40 years and The slide mass has continued to move for over 40 years and

the cumulative displacement exceeds 30 meters in some areas.the cumulative displacement exceeds 30 meters in some areas.


PORTUGUESE BEND, PALOS PORTUGUESE BEND, PALOS VERDES PENINSULAVERDES PENINSULA


POINT FERMIN LANDSLIDEPOINT FERMIN LANDSLIDE The Point Fermin landslide originally consisted of The Point Fermin landslide originally consisted of

about 10.5 acres that began sliding in 1929. about 10.5 acres that began sliding in 1929.

More movement in the early 1940’s was More movement in the early 1940’s was discovered when broken water pipes appeared. discovered when broken water pipes appeared.

Movement was slowed during the early 1960’s, Movement was slowed during the early 1960’s, however, damage to houses was enough to force however, damage to houses was enough to force evacuation of areaevacuation of area


POINT FERMIN LANDSLIDEPOINT FERMIN LANDSLIDE


SLUMPSSLUMPS


La Conchita, Ventura, CA

La Conchita Slide


FLOWS: LAHAR, DEBRIS, FLOWS: LAHAR, DEBRIS, SOLIFLUCTION, AND EARTHFLOWSOLIFLUCTION, AND EARTHFLOW

LaharLahar: combination of volcanic ash, mud and : combination of volcanic ash, mud and water flowing down a stratovolcano during an water flowing down a stratovolcano during an eruptioneruption

Debris FlowDebris Flow: combination of weathered rock, : combination of weathered rock, water and mud flowing out of canyons during water and mud flowing out of canyons during extreme rain eventsextreme rain events– Alluvial Fans: formation of ramps along at mouths of Alluvial Fans: formation of ramps along at mouths of

canyons in arid areascanyons in arid areas SolifluctionSolifluction: slow down slope movement of upper : slow down slope movement of upper

layers of weathered tundra soils; form large lobes layers of weathered tundra soils; form large lobes on slopeon slope

EarthflowEarthflow: downslope viscous flow of fine-grained : downslope viscous flow of fine-grained materials saturated with water under the influence materials saturated with water under the influence of gravityof gravity


LAHARLAHAR


DEBRIS FLOWDEBRIS FLOW


CONTROLLING DEBRIS FLOWCONTROLLING DEBRIS FLOW

Los Angeles County Flood Control Los Angeles County Flood Control developed two types of basins to developed two types of basins to attempt control of material flowing attempt control of material flowing out of San Gabriel Mountains into out of San Gabriel Mountains into foothill communitiesfoothill communities


DEBRIS and CATCHMENT BASINSDEBRIS and CATCHMENT BASINS


HOW DEBRIS BASINS WORKHOW DEBRIS BASINS WORK


WHEN DEBRIS BASINS FAILWHEN DEBRIS BASINS FAIL

Winter, 2010, La Cañada-Flintridge Debris Basin failure

SOLIFLUCTION


SOLIFLUCTION: TUNDRA SOILSSOLIFLUCTION: TUNDRA SOILS


SOIL CREEPSOIL CREEP

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