Weathering, Erosion, Weathering, Erosion, Deposition, and LandscapesDeposition, and Landscapes

forces at work

© Lisa Michalek

WeatheriWeatheringng

The The breakdowbreakdown of rocks n of rocks due to due to physical physical or or chemical chemical changeschanges

Physical WeatheringPhysical Weathering Changes the size and/or shape of a rock without Changes the size and/or shape of a rock without

changing the chemical compositionchanging the chemical composition In In frost actionfrost action, water seeps into cracks in rocks. , water seeps into cracks in rocks.

The water expands as The water expands as it freezes and makes it freezes and makes cracks in the rock a cracks in the rock a little larger little larger

When the When the ice melts and the liquid ice melts and the liquid evaporates, the rock evaporates, the rock is left more porousis left more porous

Over time, the freezing Over time, the freezing and melting in the cracks and melting in the cracks will cause the rock to will cause the rock to crumblecrumble

Physical WeatheringPhysical Weathering Plant roots grow in rock Plant roots grow in rock

crevices and gradually push crevices and gradually push the rock apartthe rock apart

Animals that burrow Animals that burrow beneath the ground will beneath the ground will expose new rock surfaces to expose new rock surfaces to weatheringweathering

AbrasionAbrasion occurs when rock occurs when rock particles are carried particles are carried in water, they in water, they bump and rub bump and rub against other rocksagainst other rocks

Chemical WeatheringChemical Weathering When rocks are exposed to the When rocks are exposed to the

atmosphere and hydrosphere, they atmosphere and hydrosphere, they often undergo changes in the often undergo changes in the chemical composition of rock, forming chemical composition of rock, forming new substancesnew substances

Usually requires heat and water to Usually requires heat and water to bring about chemical changesbring about chemical changes Therefore, it takes place more rapidly in Therefore, it takes place more rapidly in

warm, moist climateswarm, moist climates Observe an animation of cave formation.

Soil FormationSoil Formation Soil is a mixture of Soil is a mixture of

weathered rock and organic weathered rock and organic remains the usually covers remains the usually covers bedrockbedrock

The weathering of soil The weathering of soil produces horizon layersproduces horizon layers The top layer is usually the The top layer is usually the

best for growing crops best for growing crops because it is rich in organic because it is rich in organic remains called humusremains called humus

The next layer is usually The next layer is usually mineral enriched from mineral enriched from groundwater transporting groundwater transporting mineralsminerals

The lowest layer is composed The lowest layer is composed of broken-up bedrockof broken-up bedrock

Soil FormationSoil Formation

Erosion of SedimentsErosion of Sediments SedimentsSediments are rocks that have been are rocks that have been

broken into fragmentsbroken into fragments ErosionErosion is the transporting of is the transporting of

sediments away from their sediments away from their place of origin and place of origin and depositing them depositing them elsewhereelsewhere Gravity, water, Gravity, water,

wind, and ice wind, and ice erode sedimentserode sediments

Forces of Erosion and Deposition

The 1st type of Erosion and Deposition is: Gravity

-Causes the downward movement of sediments called mass movement

a. A sign of gravity erosion: Landslide – soil, rocks, & boulders move down a slope or off a cliff

Landslide (slow loading)

LANDSLIDE

Another sign of Gravity causing Erosion: :

b. Mudflow – water mixes with rock and soil and moves down a slope. Usually happens after rain and water content can be as high as 60%.

A sign of gravity erosion: Slump

Slump – loose, water-filled earth (permeable) sits on top of a water proof (impermeable) layer. The loose earth changes position.

Slump animation

Slump

Another sign of gravity erosion: Creep

is a very, very slow form of mass movement. It's just a slow adjustment of soil and rocks. Gravity always causes the rocks and soil to settle just a little farther down slope than where they started from.

Creep

Erosion by WaterErosion by Water The smallest particles are carried in The smallest particles are carried in

solutionsolution The largest and most dense particles are The largest and most dense particles are

rolled or bounced along the streambedrolled or bounced along the streambed Particles of low density, such as organic Particles of low density, such as organic

remains, are carried along the surface by remains, are carried along the surface by flotationflotation

Deposition waterfall

Velocity of StreamsVelocity of Streams The velocity of a stream is controlled by The velocity of a stream is controlled by

the slope and the amount of water flowing the slope and the amount of water flowing in the stream (in the stream (dischargedischarge). As velocity ). As velocity increases the kinetic energy also increases the kinetic energy also increases. increases.

As the stream gradient As the stream gradient increases, so does the increases, so does the velocity of the water velocity of the water flowing in the streamflowing in the stream

Velocity is also increased Velocity is also increased by an increase in the by an increase in the quantity of water quantity of water in the streamin the stream

Velocity of StreamsVelocity of Streams There is a direct There is a direct

relationship relationship between the between the velocity of a velocity of a stream and the stream and the size of the size of the particles it can particles it can transporttransport

Large grains of Large grains of sediment can sediment can only be eroded only be eroded by fast-moving by fast-moving waterwater

Velocity of StreamsVelocity of Streams Streams with broad, flat valleys often develop Streams with broad, flat valleys often develop

S-shaped curves called S-shaped curves called meandersmeanders At the bends in the stream, the fastest-At the bends in the stream, the fastest-

flowing water swings to the outside of the flowing water swings to the outside of the bends, causing erosion along the outer bankbends, causing erosion along the outer bank

The slowest moving water stays to the inside The slowest moving water stays to the inside of the bends, causing depositionof the bends, causing deposition

Meander oxbow lake waterfall waterfall

Erosion by WindErosion by Wind Wind can pick up loose rock materials, Wind can pick up loose rock materials,

such as sand, silt, and clay, and carry such as sand, silt, and clay, and carry them awaythem away

Wind erosion occurs mostly in dry areas, Wind erosion occurs mostly in dry areas, such as deserts and beachessuch as deserts and beaches

Sand blown by Sand blown by the wind can the wind can erode down erode down material on material on a rocka rock’’s surfaces surface

dune formationdune formation

Wind erosion happens when the soil is left unprotected from the strong winds. The loss of topsoil lowers the quality of the soil. This makes it more expensive and harder to grow good crops.

formation of an arch

Erosion by WindErosion by Wind

Erosion by IceErosion by Ice

If more snow accumulates in the winter If more snow accumulates in the winter than melts in the summer, the snow on than melts in the summer, the snow on the bottom turns to ice glacial retreatthe bottom turns to ice glacial retreat

If it becomes thick enough, its weight will If it becomes thick enough, its weight will cause it to move under the pull of gravitycause it to move under the pull of gravity

A A glacierglacier is a large is a large mass of moving icemass of moving ice

As a glacier moves, As a glacier moves, it carries, pushes, it carries, pushes, and drags loose and drags loose rock materialrock material

Erosion by IceErosion by Ice The glacier, with The glacier, with

pieces of rock, pieces of rock, smoothes, striates smoothes, striates (scratches), (scratches), and grooves bedrockand grooves bedrock

As a glacier moves As a glacier moves through a valley, it will through a valley, it will make a U-shape make a U-shape instead of a V-shape instead of a V-shape caused by watercaused by water

When the ice melts, When the ice melts, unsorted rocks and unsorted rocks and boulders are left boulders are left scattered around on scattered around on hilltops and sides of hilltops and sides of valleysvalleys

Plucking

Plucking occurs when ice flows into or refreezes in fractures in the bedrock. The ice wedges and removes blocks of bedrock and incorporates it into the glacier. This process is most rapid in areas where water is refreezing near the bed.

Plucking animation

Formed by a glacier

Formed by a glacier

HORN

Glacial Lake-formed by a glacier

DepositionDeposition

When an agent of erosion deposits, When an agent of erosion deposits, or lays down particles and fragments or lays down particles and fragments of earth materials (sediments)of earth materials (sediments)

Also called Also called sedimentationsedimentation Most deposition takes place in waterMost deposition takes place in water

Deposition FactorsDeposition Factors Particle SizeParticle Size

Smaller particles (clay and silt) settle Smaller particles (clay and silt) settle more slowly than cobbles and bouldersmore slowly than cobbles and boulders

Particle ShapeParticle Shape Friction between water and the surfaces Friction between water and the surfaces

of particles slows down settlingof particles slows down settling Smooth, rounded Smooth, rounded

particles settle particles settle more slowlymore slowly

Deposition FactorsDeposition Factors

Particle DensityParticle Density Denser particles settle faster, less dense Denser particles settle faster, less dense

particles take more time to settleparticles take more time to settle Settling Rate and TimeSettling Rate and Time

Sediments that settle at a Sediments that settle at a faster rate require less timefaster rate require less time

As the rate of settling As the rate of settling increases, the settling increases, the settling time decreasestime decreases

Sorting of SedimentsSorting of Sediments

HorizontalHorizontal sorting sorting occurs at the end of occurs at the end of streamsstreams The smaller sediments The smaller sediments

can be carried a greater can be carried a greater distance from shoredistance from shore

VerticalVertical sorting occurs when a sorting occurs when a landscape dumps a variety of landscape dumps a variety of particle sizes in to still waterparticle sizes in to still water

Deposition by WindDeposition by Wind

Usually sorts sediments by sizeUsually sorts sediments by size Cross bedding layers meet a different Cross bedding layers meet a different

anglesangles

Deposition by GravityDeposition by Gravity

At the base of a cliff, At the base of a cliff, where pieces of where pieces of weathered rock weathered rock have fallen, you will have fallen, you will find pieces of many find pieces of many different sizesdifferent sizes

The sediments are The sediments are not sortednot sorted

Deposition by GlaciersDeposition by Glaciers Occurs when a glacier Occurs when a glacier

melts and sediments melts and sediments are releasedare released

Glacial erraticsGlacial erratics are are large rocks that have large rocks that have been transported by been transported by glacial ice without being glacial ice without being broken into small broken into small particlesparticles They are often found They are often found

high above stream high above stream valleysvalleys

Rounding and striations Rounding and striations (scratches) indicate (scratches) indicate transport by glacierstransport by glaciers

Alpine GlaciersAlpine Glaciers

Also known as Also known as valley valley glaciersglaciers, , occur in occur in mountain mountain regions, and regions, and may carve may carve out U-shaped out U-shaped valleys with valleys with their moving their moving iceice

Continental GlaciersContinental Glaciers

Also known as Also known as ice sheetsice sheets causes causes sculpting of the sculpting of the land as rocks land as rocks are carried are carried within the within the glacier or glacier or dragged under dragged under the flowing icethe flowing ice

Glacial FeaturesGlacial Features

Glacial PolishGlacial Polish – – when glaciers act like when glaciers act like sandpaper, grinding sandpaper, grinding the jagged edges the jagged edges from the mountains from the mountains and smoothing hard and smoothing hard bedrock surfacesbedrock surfaces

StriationStriation – parallel – parallel grooves and scratches grooves and scratches in the bedrock left by in the bedrock left by the rocks in the the rocks in the glacierglacier

Glacial FeaturesGlacial Features DrumlinsDrumlins – accumulation of rock and soil – accumulation of rock and soil

that builds up in front of the flowing icethat builds up in front of the flowing ice

MorainesMoraines – where the ice front stops its – where the ice front stops its southward advance, piles of southward advance, piles of unsorted soil and rock remainunsorted soil and rock remain

Glacial FeaturesGlacial Features KettlesKettles – Low spots in the glacial – Low spots in the glacial

deposits and places where large, deposits and places where large, buried ice blocks melt leave these buried ice blocks melt leave these dry depressions dry depressions and ponds and ponds called called Kettle LakesKettle Lakes

North American North American Continental GlaciationContinental Glaciation

The Oceans and The Oceans and CoastsCoasts

Seawater covers almost 71% Seawater covers almost 71% of our planetof our planet

The average depth is about 4 km The average depth is about 4 km (3 mi)(3 mi)

One Liter of seawater One Liter of seawater contains about 3.5% of contains about 3.5% of dissolved solidsdissolved solids Sodium chloride (table Sodium chloride (table

salt) is the most commonsalt) is the most common When evaporation of ocean When evaporation of ocean

water causes the salts to water causes the salts to become too concentrated to become too concentrated to stay in solution, they are stay in solution, they are precipitated as sedimentprecipitated as sediment

The Oceans and CoastsThe Oceans and Coasts

The edges of the oceans are places of The edges of the oceans are places of change caused by the action of waves change caused by the action of waves and long shore currents long shore driftand long shore currents long shore drift

Beach sediments are rounded and Beach sediments are rounded and reduced in size by abrasion as the reduced in size by abrasion as the energy in the breaking waves causes energy in the breaking waves causes the particles to rub against one anotherthe particles to rub against one another

The Oceans and CoastsThe Oceans and Coasts Sand is often transported along the Sand is often transported along the

beach and just outside the breaking beach and just outside the breaking waves in the zone of waves in the zone of longshore longshore transporttransport

This movement of sand builds the This movement of sand builds the features of the features of the ocean shorelines ocean shorelines including sand bars, including sand bars, barrier islands, barrier islands, and sand spitsand sand spits

beach processesbeach processes

LandscapesLandscapes

A region on EarthA region on Earth’’s surface with physical s surface with physical features, such as hills, valleys, and features, such as hills, valleys, and streamsstreams

The shape (The shape (topographytopography) and ) and composition of the landscape is composition of the landscape is determined by the climate, bedrock, determined by the climate, bedrock, geologic structures, and human activitiesgeologic structures, and human activities

Topographic Topographic reliefrelief is is the change in elevation the change in elevation between the highest between the highest and the lowest placesand the lowest places

Landscape RegionsLandscape Regions MountainMountain landscapes have the greatest landscapes have the greatest

relief between the highest peaks and the relief between the highest peaks and the deepest valleysdeepest valleys

A great variety of rock types are commonA great variety of rock types are common Mountains are common where converging Mountains are common where converging

tectonic plates collidetectonic plates collide Stream gradients are Stream gradients are

high, and the fast high, and the fast moving streams quickly moving streams quickly erode deep valleys erode deep valleys between the between the mountain peaksmountain peaks

Landscape RegionsLandscape Regions PlateauPlateau landscapes are relatively flat landscapes are relatively flat

or rolling uplands where streams have or rolling uplands where streams have cut deep valleyscut deep valleys

Commonly underlain by flat layers of Commonly underlain by flat layers of sedimentary rocksedimentary rock

Less topographic Less topographic relief than mountains relief than mountains but more relief than but more relief than the plainsthe plains

Landscape RegionsLandscape Regions

PlainsPlains have the least topographic have the least topographic reliefrelief

They may contain a few small hills, They may contain a few small hills, but are generally flat and at low but are generally flat and at low elevationelevation

Commonly underlain by flat layers of Commonly underlain by flat layers of sedimentary rocksedimentary rock

Climate Influence on Climate Influence on RegionsRegions

Moist, Moist, HumidHumid climates usually have climates usually have rounded landscapesrounded landscapes

Slopes are not as steep because moist Slopes are not as steep because moist climates promote a protective cover of climates promote a protective cover of vegetationvegetation Plants cover protects the soil Plants cover protects the soil

from rapid runoff and erosionfrom rapid runoff and erosion

Climate Influence on Climate Influence on RegionsRegions

AridArid (dry) climates usually produce (dry) climates usually produce thin soils with little humusthin soils with little humus

With little plant cover to protect the With little plant cover to protect the soil, sediment is carried away during soil, sediment is carried away during rainfallrainfall Large areas of exposed bedrock and Large areas of exposed bedrock and

steep rock faces are the resultsteep rock faces are the result

Landscape Regions of the Landscape Regions of the USUS

Landscape Regions of NYLandscape Regions of NY

Drainage PatternsDrainage Patterns Harder rocks will form hills and ridgesHarder rocks will form hills and ridges Erosion of the weaker rock will make Erosion of the weaker rock will make

the major valleysthe major valleys Streams will tend to follow zones of Streams will tend to follow zones of

weaker rock and flow downhillweaker rock and flow downhill

Drainage PatternsDrainage Patterns

Human Activities Human Activities Can Affect LandscapesCan Affect Landscapes

Farming and construction projects can Farming and construction projects can accelerate erosion and effect accelerate erosion and effect landscape developmentlandscape development

Farmers and engineers must be Farmers and engineers must be guided in planning their projects by guided in planning their projects by appropriate conservation practicesappropriate conservation practices