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

© Lisa Michalek

WeatheriWeatheringng

The The breakdowbreakdown of rocks n of rocks due to due to physical physical or or chemical chemical changes.changes.

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 composition.changing 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 porous.is 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 crumble.crumble.

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

crevices and gradually push crevices and gradually push the rock apart.the 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 weathering.weathering.

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 rocks.against other rocks.

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

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

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

warm, moist climates.warm, moist climates.

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

rock and organic remains the rock and organic remains the usually covers bedrock.usually covers bedrock.

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

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

The next layer is usually The next layer is usually mineral enriched from mineral enriched from groundwater transporting groundwater transporting minerals.minerals.

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

Soil FormationSoil Formation

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

broken into fragments.broken 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 elsewhere.elsewhere. Gravity, water, Gravity, water,

wind, and ice wind, and ice erode sediments.erode sediments.

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

solution.solution. The largest and most dense particles are The largest and most dense particles are

rolled or bounced along the streambed.rolled 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 remains, are carried along the surface by flotation.by flotation.

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

by the slope and the amount of water by the slope and the amount of water flowing in the stream (flowing in the stream (dischargedischarge).).

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 stream.flowing 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 stream.in 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 transport.transport.

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

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

develop S-shaped curves called develop 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 bends, causing erosion along the outer bank.bank.

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

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 away.them away.

Wind erosion occurs mostly in dry areas, Wind erosion occurs mostly in dry areas, such as deserts and beaches.such 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 rock’s surface.a rock’s surface.

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.the bottom turns to ice.

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

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

As a glacier moves, As a glacier moves, it carries, pushes, it carries, pushes, and drags loose and drags loose rock material.rock 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 bedrock.and 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 water.caused 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 valleys.valleys.

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 water.Most 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 boulders.more slowly than cobbles and boulders.

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

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

particles settle particles settle more slowly.more slowly.

Deposition FactorsDeposition Factors

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

particles take more time to settle.particles 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 time.faster rate require less time.

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

Sorting of SedimentsSorting of Sediments

HorizontalHorizontal sorting sorting occurs at the end of occurs at the end of streams.streams. The smaller sediments The smaller sediments

can be carried a greater can be carried a greater distance from shore.distance 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 water.particle sizes in to still water.

Deposition by WindDeposition by Wind Usually sorts sediments by size.Usually sorts sediments by size. Cross bedding layers meet a different Cross bedding layers meet a different

angles.angles.

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 sizes.different sizes.

The sediments are The sediments are not sorted.not sorted.

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

melts and sediments are melts and sediments are released.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 particles.particles. They are often found high They are often found high

above stream valleys.above stream valleys. Rounding and striations Rounding and striations

(scratches) indicate (scratches) indicate transport by glaciers.transport by glaciers.

Alpine GlaciersAlpine Glaciers

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

Continental GlaciersContinental Glaciers

Also known as Also known as ice ice sheetssheets causes causes sculpting of the sculpting of the land as rocks are land as rocks are carried within the carried within the glacier or dragged glacier or dragged under the flowing under the flowing ice.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 surfaces.bedrock 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 glacier.glacier.

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

that builds up in front of the flowing ice.that 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 remain.unsorted 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 Lakes.Kettle 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 planet.of 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 solids.dissolved solids. Sodium chloride (table Sodium chloride (table

salt) is the most common.salt) 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 sediment.precipitated as sediment.

The Oceans and CoastsThe Oceans and Coasts

The edges of the oceans are places The edges of the oceans are places of change caused by the action of of change caused by the action of waves and longshore currents.waves and longshore currents.

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 the particles to rub against one another.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 spits.and sand spits.

LandscapesLandscapes

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

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 activities.geologic 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 places.and 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 valleys.deepest valleys.

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

tectonic plates collide.tectonic 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 peaks.mountain 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 valleys.cut deep valleys.

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

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

Landscape RegionsLandscape Regions

PlainsPlains have the least topographic relief. have the least topographic relief. They may contain a few small hills, but They may contain a few small hills, but

are generally flat and at low elevation.are generally flat and at low elevation. Commonly underlain by flat layers of Commonly underlain by flat layers of

sedimentary rock.sedimentary rock.

Climate Influence on Climate Influence on RegionsRegions

Moist, Moist, HumidHumid climates usually have climates usually have rounded landscapes.rounded 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 vegetation.vegetation. Plants cover protects the soil Plants cover protects the soil

from rapid runoff and erosion.from rapid runoff and erosion.

Climate Influence on Climate Influence on RegionsRegions

AridArid (dry) climates usually produce (dry) climates usually produce thin soils with little humus.thin 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 rainfall.rainfall. Large areas of exposed bedrock and steep Large areas of exposed bedrock and steep

rock faces are the result.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 ridges.Harder rocks will form hills and ridges. Erosion of the weaker rock will make Erosion of the weaker rock will make

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

weaker rock and flow downhill.weaker 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 development.landscape 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 practices.appropriate conservation practices.