Weathering of RocksWeathering of Rocks

Hoodoos

More Resistant layerMore Resistant layer

Breaking and Removing rock1. Weathering - the disintegration and

decomposition of rock at or near the

surface.

2. Erosion – the transport of weathered

material by water, wind, ice and

gravity.

Weathering in the Rock Cycle

SedimentaryRocks

IgneousRocks

MetamorphicRocks

Magma

Sediment

Pressure And Cementation

Weathering and Erosion

Weathering

And Erosion

Heat and Pressure

CoolingHeat

Heat

Pressure

Wea

ther

ing

And

Ero

sion

*Types of Weathering*Types of Weathering

Mechanical –Mechanical – physical breakdown of physical breakdown of rocks with rocks with NO changeNO change in in composition.composition.

Chemical –Chemical – chemical alteration and chemical alteration and decomposition of rocks by decomposition of rocks by chemical reactions.chemical reactions.

Mechanical Weathering makes smaller pieces and exposes more

surface area to weathering processes

*Types of Mechanical Weathering*Types of Mechanical Weathering

1.1. Ice Wedging – water freezes in cracks and Ice Wedging – water freezes in cracks and expands them causing rocks to break expands them causing rocks to break apart.apart.

Ice Wedging

*Types of Mechanical Weathering*Types of Mechanical Weathering

2. Organic Activity – roots break apart rocks.2. Organic Activity – roots break apart rocks.

Organic Activity

Tree along 460 near Princeton that was saved Tree along 460 near Princeton that was saved by building a huge cement wall with drainageby building a huge cement wall with drainage

*Types of Mechanical Weathering*Types of Mechanical Weathering

3. Exfoliation and Jointing because of 3. Exfoliation and Jointing because of pressure release also break apart rocks.pressure release also break apart rocks.

Exfoliation

Exfoliation

Results of Jointing

*Types of Mechanical Weathering*Types of Mechanical Weathering

4. Abrasion –rounding or smoothing by 4. Abrasion –rounding or smoothing by water, wind, or glacierswater, wind, or glaciers

Wind, water and glaciers also Wind, water and glaciers also erode/deposit sediments.erode/deposit sediments.

Examples: Glacial Striations

Glacial Polish

Glaciers smooth and/or scratch

rocks.

*Water transport in rivers *Water transport in rivers smooths and rounds rocks. smooths and rounds rocks.

http://www.hariomtradeint.co.uk/images/MixRiverPebbles_f.jpg

*Wind creates ventifacts *Wind creates ventifacts (smoothed surfaces and (smoothed surfaces and

erosion)erosion)

Wind and water work together

*Wind Deposition creates Dunes

*Types of Chemical Weathering*Types of Chemical Weathering Hydrolysis - any reaction in which

water participates. Also includes acid.

*Types of Chemical Weathering*Types of Chemical Weathering

1. Rust (oxidation) – caused by water and 1. Rust (oxidation) – caused by water and

oxygenoxygen

2. Carbonation (caves) – KARST topography 2. Carbonation (caves) – KARST topography

forms when carbonic acid (formed by forms when carbonic acid (formed by

water and carbon dioxide) reacts with water and carbon dioxide) reacts with

limestone (Calcium Carbonate) and limestone (Calcium Carbonate) and

converts it to converts it to solublesoluble Calcium Bicarbonate. Calcium Bicarbonate.

*2a. Stalactites and stalagmites form *2a. Stalactites and stalagmites form

from carbonate deposits from from carbonate deposits from dripping water in caves.dripping water in caves.

*2b. Sinkholes can also cause *2b. Sinkholes can also cause

pollution problems if they connect pollution problems if they connect directly to the water table.directly to the water table.

Typical SinkholeTypical Sinkhole

Not a Typical Sinkhole…Not a Typical Sinkhole…

*Types of Chemical Weathering*Types of Chemical Weathering3.3. Acids in mosses and roots can react with Acids in mosses and roots can react with

minerals in rocks minerals in rocks

and dissolve them.and dissolve them.

4.4. Changing of feldspar into clay (kaolin) by Changing of feldspar into clay (kaolin) by

hydrolysis.hydrolysis.

5.5. Dissolving by water.Dissolving by water.

*Factors influencing Weathering *Factors influencing Weathering RatesRates

1.Rock Composition – sedimentary rocks weather more rapidly than metamorphic or igneous. Also, quartz is resistant to weathering.

2.Rock Surface area – more surface exposed, more rapidly weathered.

3.Topography – high elevation and steep slopes weather more rapidly.

4.Climate – variable (freezes and thaws) and hot/ humid cause rapid weathering.

Benefits of WeatheringBenefits of Weathering

• Produces regolith (rock fragments) Produces regolith (rock fragments)

clay, sand, and gravel clay, sand, and gravel

• Produces mineralsProduces minerals

• Creates soilCreates soil

SoilSoil is made of loose, weathered is made of loose, weathered rock, minerals, air and organic rock, minerals, air and organic

material (humus).material (humus).

Soil Profile(fill in the blanks)Soil Profile(fill in the blanks)

RR

0- Leaf Litter0- Leaf Litter

B- Clay and B- Clay and Leached Leached MineralsMinerals

R-Bedrock or R-Bedrock or Parent Rock Parent Rock

A-HumusA-Humus

C- Partially C- Partially Weathered Weathered

BedrockBedrock

Soil ProfileSoil Profile

In a cross-In a cross-section of soil, section of soil,

various various horizonshorizons are formed.are formed.

AA Horizon: Topsoil Horizon: Topsoil

This layer is This layer is usually loose usually loose

and crumbly with and crumbly with a significant a significant amount of amount of

organic matter organic matter (HUMUS).(HUMUS).

((OO is leaf litter) is leaf litter)

AA Horizon: Topsoil Horizon: Topsoil

Most Most productiveproductive layer of soil.layer of soil.

ConservationConservation efforts are efforts are

focused here!focused here!

BB Horizon: Subsoils Horizon: Subsoils Subsoils are Subsoils are usually light, usually light,

dense, dense, clayclay-rich -rich with some organic with some organic

matter. This is matter. This is where where minerals minerals

leachedleached from the from the AA horizon horizon

accumulate.accumulate.

CC Horizon: Transition Horizon: Transition

Partially Partially weatheredweathered parent parent

material with material with little/no humus.little/no humus.

BedrockBedrock

Below the C Below the C horizon the horizon the

unweathered unweathered bedrockbedrock will be will be

found. found.

Climate and SoilClimate and Soil

TropicsTropics – thick, – thick, unfertile soils unfertile soils

called called laterites.laterites.Arctic or DesertArctic or Desert

– thin, made – thin, made mostly of mostly of regolithregolith

Topography and SoilTopography and Soil

SlopesSlopes – thin – thin

and dry topsoiland dry topsoil

LowlandsLowlands – thick, – thick,

wet soils with wet soils with

humushumus

Erosion Erosion ControlControl

Creating a Creating a soil soil condition condition that is that is resistant resistant to erosionto erosion

Control Practices and Control Practices and Structures for FarmsStructures for Farms

TerracingTerracing,,Crop Crop rotation rotation and Wind and Wind BreaksBreaks

Wind Erosion

Factors that Factors that DecreaseDecrease Wind Wind ErosionErosion

CloddinessCloddiness

Crop residueCrop residue

RidgesRidges

BarriersBarriers

Mass WastingMass Wasting

The downslope movement of unconsolidated Earth material due to gravity.

Increasing Severity of Mass WastingIncreasing Severity of Mass Wasting

Slump- quick downward movement of a block of soil.

Rock Slides

Creep-slow movement of soil down a slope due to expansion and freezing.

Creep

Mudflows-very fast downward Mudflows-very fast downward movement of water and mudmovement of water and mud

The StabilityStability of soil is reducedreduced by:

1. Adding water to the material of a slope

2. Increasing the steepness of the slope

3. Removing material from the lower

part of the slope

4. Earthquakes

5. Removal of vegetation (increases

runoff)

Erosion Erosion Created Created

LandformsLandformsMountainsMountains

erode to erode to peneplainspeneplains

Sometimes Sometimes monadnocks monadnocks (resistant knobs of rock)(resistant knobs of rock) are are exposed.exposed.

MountainsMountains erode finally to erode finally to plainsplains

Plateaus (large high flat areas)Plateaus (large high flat areas) erode to form erode to form mesas (smaller mesas (smaller high table-like structures)high table-like structures) and and buttes (small narrow buttes (small narrow columns)columns)

Engineering Solutions

Rock Nets

Soil Nailing

Avalanche Avalanche BarriersBarriers

(Switzerland)(Switzerland)