WeatheringWeathering Geomorphology is the science of the origin, evolution, Geomorphology is the science of the origin, evolution,

form and spatial distribution of landforms.form and spatial distribution of landforms. ““Geo” = “earth”; “morphos= “shape”; “ology” = science; Geo” = “earth”; “morphos= “shape”; “ology” = science;

hence, “science of the shape of the earth.” hence, “science of the shape of the earth.” Landscapes continually adjust toward an equilibrium Landscapes continually adjust toward an equilibrium

state. Weathering and erosion continually try to adjust state. Weathering and erosion continually try to adjust the landscape toward an equilibrium state, an ultimate the landscape toward an equilibrium state, an ultimate base level (sea level?), while uplifting processes base level (sea level?), while uplifting processes continually attempt to keep the landscape from reaching continually attempt to keep the landscape from reaching that base level. This constant, fluctuating balance that base level. This constant, fluctuating balance between weathering/erosion and uplift is called between weathering/erosion and uplift is called Dynamic Dynamic EquilibriumEquilibrium..

WeatheringWeathering Factors influencing the equilibrium state:Factors influencing the equilibrium state:

rock materialsrock materials rock structurerock structure climateclimate topographic relieftopographic relief

Equilibrium is approached episodically through Equilibrium is approached episodically through geomorphic geomorphic thresholdsthresholds – points at which destabilizing energy overcomes – points at which destabilizing energy overcomes resistance against movement or change.resistance against movement or change.

Landscapes have inertia – the tendency of matter to remain at rest Landscapes have inertia – the tendency of matter to remain at rest unless affected by an outside force. When there is a change in rock unless affected by an outside force. When there is a change in rock materials, structure, climate, or relief, the landscape reaches an materials, structure, climate, or relief, the landscape reaches an unstable condition wherein there may be a sudden change.unstable condition wherein there may be a sudden change.

WeatheringWeathering Most Most rocks and and minerals are formed deep are formed deep

within the Earth's crust where within the Earth's crust where temperatures and pressures differ greatly temperatures and pressures differ greatly from the surface.from the surface.

The physical and chemical nature of The physical and chemical nature of materials formed in the Earth’s interior are materials formed in the Earth’s interior are characteristically in disequilibrium with characteristically in disequilibrium with conditions occurring on the surface. conditions occurring on the surface.

WeatheringWeathering Because of this disequilibrium, these materials Because of this disequilibrium, these materials

are easily attacked, decomposed, and eroded by are easily attacked, decomposed, and eroded by various chemical and physical surface various chemical and physical surface processes. processes.

Weathering - breakdown and alteration of rocks - breakdown and alteration of rocks and minerals at or near the Earth's surface into and minerals at or near the Earth's surface into products that are more in equilibrium with the products that are more in equilibrium with the conditions found in the surface environment. conditions found in the surface environment.

Weathering:Weathering: Regolith, Soil, and Parent MaterialsRegolith, Soil, and Parent Materials

WeatheringWeathering Weathering products are a major source of Weathering products are a major source of

sediments for sediments for erosion and and deposition..

Many types of Many types of sedimentary rocks are composed are composed of particles that have been weathered, eroded, of particles that have been weathered, eroded, transported, and finally deposited in basins.transported, and finally deposited in basins.

Weathering also contributes to the formation of Weathering also contributes to the formation of soil by providing mineral particles like by providing mineral particles like sand,, silt, , andand clay..

WeatheringWeathering Elements and and compounds extracted from rocks and extracted from rocks and

minerals by weathering processes supply nutrients for minerals by weathering processes supply nutrients for plant uptake.plant uptake.

The oceans are saline as a result of the release of ion The oceans are saline as a result of the release of ion salts from rocks and minerals on the continents. salts from rocks and minerals on the continents. Leaching and and runoff transport these ions from land to the transport these ions from land to the ocean basins where they accumulate in seawater.ocean basins where they accumulate in seawater.

So we see, weathering is a process that is fundamental to So we see, weathering is a process that is fundamental to many other aspects of the many other aspects of the hydrosphere, , lithosphere, and , and biosphere. .

WeatheringWeathering

There are three broad categories of There are three broad categories of weathering mechanisms:weathering mechanisms:

ChemicalChemical

PhysicalPhysical

BiologicalBiological

WeatheringWeathering The process of weathering can result in the following The process of weathering can result in the following

three outcomes on three outcomes on rocks and and minerals::

The complete loss of particular The complete loss of particular atoms or or compoundscompounds from the weathered surface.from the weathered surface.

The addition of specific atoms or compounds to the The addition of specific atoms or compounds to the weathered surface.weathered surface.

A breakdown of one mass into two or more masses, with A breakdown of one mass into two or more masses, with no chemical change in the mineral or rock.no chemical change in the mineral or rock.

WeatheringWeathering The residue of weathering consists of chemically altered and The residue of weathering consists of chemically altered and

unaltered materials.unaltered materials.

The most common unaltered residue is The most common unaltered residue is quartzquartz..

Many of the chemically altered products of weathering become very Many of the chemically altered products of weathering become very simple small compounds or nutrient simple small compounds or nutrient ionsions that can be dissolved or that can be dissolved or transported by water, released to the atmosphere as a gas, or taken transported by water, released to the atmosphere as a gas, or taken up by plants for nutrition.up by plants for nutrition.

Some of the products of weathering, less resistant alumino-silicate Some of the products of weathering, less resistant alumino-silicate minerals, become clay particles.minerals, become clay particles.

Other altered materials are reconstituted by sedimentary or Other altered materials are reconstituted by sedimentary or metamorphicmetamorphic processes to become new rocks and minerals. processes to become new rocks and minerals.

Physical WeatheringPhysical Weathering

Physical weatheringPhysical weathering is the breakdown of is the breakdown of mineral or rock material by entirely mineral or rock material by entirely mechanical methods, without any mechanical methods, without any chemical change in the rock material, chemical change in the rock material, brought about by a variety of causes. brought about by a variety of causes. Some of the forces originate within the Some of the forces originate within the rock or mineral, while others are applied rock or mineral, while others are applied externally. Both of these stresses lead to externally. Both of these stresses lead to strain and the rupture of the rock.strain and the rupture of the rock.

Physical Weathering ProcessesPhysical Weathering Processes

AbrasionAbrasion - mechanical wearing or - mechanical wearing or grinding of a rock surface; normally occurs grinding of a rock surface; normally occurs through the through the erosionalerosional transport of material transport of material by wind, water, or ice.by wind, water, or ice.

Frost actionFrost action involves the 9% increase in involves the 9% increase in volume of water as it freezes, overcoming volume of water as it freezes, overcoming the low tensile strength of rock.the low tensile strength of rock.

Physical Weathering ProcessesPhysical Weathering Processes Boulders rounded as wave action rolled them against Boulders rounded as wave action rolled them against

one anotherone another

Physical Weathering ProcessesPhysical Weathering Processes Delicate Arch, Arches National Park, Utah- differential weathering of resistant Delicate Arch, Arches National Park, Utah- differential weathering of resistant

rock strata has preserved the arch beneath the structure as surrounding rock rock strata has preserved the arch beneath the structure as surrounding rock was eroded away. Note person in inset for scale.was eroded away. Note person in inset for scale.

Physical Weathering ProcessesPhysical Weathering Processes CrystallizationCrystallization – crystal growth - the change from liquid to solid – crystal growth - the change from liquid to solid

crystalline form produces a volumetric change that overcomes the crystalline form produces a volumetric change that overcomes the low tensile strength of rock.low tensile strength of rock.

Two primary types of crystal growth in void space of rocks: ice and Two primary types of crystal growth in void space of rocks: ice and salt.salt.

Ice formation – water increases volume by 9% as it freezes, rupturing Ice formation – water increases volume by 9% as it freezes, rupturing the rock.the rock.

Especially prominent in temperate and polar regions of the earth.Especially prominent in temperate and polar regions of the earth. The threshold temperature for frost action is at least - 5° Celsius, and it is at The threshold temperature for frost action is at least - 5° Celsius, and it is at

this temperature that the most effective rupturing occurs.this temperature that the most effective rupturing occurs.

Salt formation – salt increases volume from 1 to 5 percent depending on Salt formation – salt increases volume from 1 to 5 percent depending on the temperature of the rock or mineral surface.the temperature of the rock or mineral surface.

Most common in hot arid regions, but may occur in cold climates.Most common in hot arid regions, but may occur in cold climates. Greatly enhances potential for frost weathering.Greatly enhances potential for frost weathering.

Physical Weathering ProcessesPhysical Weathering Processes Insolation weatheringInsolation weathering - t - the physical breakdown of rock he physical breakdown of rock

by expansion and contraction due to diurnal temperature by expansion and contraction due to diurnal temperature changes and the physical inability of rocks to conduct changes and the physical inability of rocks to conduct heat well.heat well.

Results in differential rates of expansion and contraction - the Results in differential rates of expansion and contraction - the surface of the rock expands more than its interior, eventually surface of the rock expands more than its interior, eventually causing the rock to rupture.causing the rock to rupture.

May also be due to variance in colors of mineral grains in rock May also be due to variance in colors of mineral grains in rock (dark colored grains absorb more heat than light colored grains (dark colored grains absorb more heat than light colored grains leading to rupture at mineral boundaries.leading to rupture at mineral boundaries.

Physical Weathering ProcessesPhysical Weathering Processes SlakingSlaking - alternate - alternate wetting and dryingwetting and drying leads to accumulation of leads to accumulation of

successive layers of “ordered” water molecules between the mineral grains successive layers of “ordered” water molecules between the mineral grains of a rock, increasing the thickness of the water such that it pulls the rock of a rock, increasing the thickness of the water such that it pulls the rock grains apart over time with great tensional stress.grains apart over time with great tensional stress.

This can happen in as little as twenty cycles of wetting and drying.This can happen in as little as twenty cycles of wetting and drying.

Pressure release jointingPressure release jointing due to due to unloadingunloading.. Erosional exposure of igneous rock masses that were created deep within the Erosional exposure of igneous rock masses that were created deep within the

earth subjects them to earth subjects them to low-pressure/low T low-pressure/low T conditions unlike those where they conditions unlike those where they were formed. As they “decompress” in all directions, jointing occurs, exposing were formed. As they “decompress” in all directions, jointing occurs, exposing them to surface weathering and decomposition.them to surface weathering and decomposition.

Horizontal Fractures Horizontal Fractures occur due to unloading of pressure with exposure;occur due to unloading of pressure with exposure;

Vertical FracturingVertical Fracturing (Spalling)(Spalling) occurs due to bending stress of sheets unloading three- occurs due to bending stress of sheets unloading three-dimensionally.dimensionally.

Leads to process called Leads to process called exfoliation.exfoliation.

Physical Weathering ProcessesPhysical Weathering ProcessesHalf Dome, Yosemite National Park, CA, a glacially eroded granite Half Dome, Yosemite National Park, CA, a glacially eroded granite

exfoliation dome (+/-5,000 ft. of relief from top to valley bottom)exfoliation dome (+/-5,000 ft. of relief from top to valley bottom)

Robert W. ChristophersonRobert W. Christopherson

Physical Weathering ProcessesPhysical Weathering ProcessesHalf Dome, Yosemite National Park, CA, east side view. The loosened slabs or Half Dome, Yosemite National Park, CA, east side view. The loosened slabs or

rock are subject to further weathering and down-slope movement.rock are subject to further weathering and down-slope movement.

Robert W. ChristophersonRobert W. Christopherson

Physical Weathering ProcessesPhysical Weathering ProcessesGreat arches form in the White Mountains of New HampshireGreat arches form in the White Mountains of New Hampshire

Bobbe ChristophersonBobbe Christopherson

Physical Weathering ProcessesPhysical Weathering ProcessesRock sheeting along Beverly Sund, Nordaustlandet Island, Arctic OceanRock sheeting along Beverly Sund, Nordaustlandet Island, Arctic Ocean

Bobbe ChristophersonBobbe Christopherson

Chemical Weathering ProcessesChemical Weathering Processes Chemical weatheringChemical weathering involves the alteration of involves the alteration of

the chemical and mineralogical composition of the chemical and mineralogical composition of the weathered material.the weathered material.

The most common chemical weathering The most common chemical weathering processes are:processes are: HydrolysisHydrolysis OxidationOxidation ReductionReduction HydrationHydration CarbonationCarbonation SolutionSolution

Chemical Weathering ProcessesChemical Weathering Processes HydrolysisHydrolysis - reaction between - reaction between mineralmineral ions and ions and

the the ionsions of water (OH of water (OH-- and H and H++)) Results in decomposition of the Results in decomposition of the rockrock surface by surface by

forming new compounds on and in rock surfaceforming new compounds on and in rock surface increases increases pHpH of the altering solution through release of the altering solution through release

of hydroxide ionsof hydroxide ions Especially effective in weathering of silicate and Especially effective in weathering of silicate and

alumino-silicate minerals because of their electrically alumino-silicate minerals because of their electrically charged crystal surfaces.charged crystal surfaces.

Ex.:Ex.:

2KAlSi3O8 + 2H+ + 2HCO3- + H2O- 2KAlSi3O8 + 2H+ + 2HCO3- + H2O- Al2Si2O5(OH)4 + 2K+ + 2HCO3- + 4SiO2 Al2Si2O5(OH)4 + 2K+ + 2HCO3- + 4SiO2

orthoclaseorthoclase carbonic acid carbonic acid weathering kaolinite weathering kaolinite silicasilica

Chemical Weathering ProcessesChemical Weathering Processes OxidationOxidation is the reaction and combination of metallic compounds and is the reaction and combination of metallic compounds and

oxygen (for example, rusting) in which the metallic element loses an oxygen (for example, rusting) in which the metallic element loses an electron to an oxygen ion.electron to an oxygen ion.

Results in the removal of one or more electrons from a compound, causing Results in the removal of one or more electrons from a compound, causing the structure to be less rigid and more unstable.the structure to be less rigid and more unstable.

Forms a common class of compounds called Forms a common class of compounds called oxidesoxides

Red and yellow staining of soils is common in tropics with Hi T and precip.Red and yellow staining of soils is common in tropics with Hi T and precip.

Ex.:Ex.:

4FeS2 + 11H2O + 15O2 4FeS2 + 11H2O + 15O2 Fe2O3 + 2Fe(OH)3 + 8H2SO4 Fe2O3 + 2Fe(OH)3 + 8H2SO4pyritepyrite water water weathering hematite limonite weathering hematite limonite hydro-sulfuric acid hydro-sulfuric acid

Chemical Weathering ProcessesChemical Weathering Processes Oxidation of iron minerals produces brilliant red color in sandstone, Oxidation of iron minerals produces brilliant red color in sandstone,

Red Rock Canyon, NevadaRed Rock Canyon, Nevada

Bobbe ChristophersonBobbe Christopherson

Chemical Weathering ProcessesChemical Weathering Processes The brilliant reds of Fe and Al oxides in soils produced by a warm, The brilliant reds of Fe and Al oxides in soils produced by a warm,

moist climate in Sumter County, GAmoist climate in Sumter County, GA

Bobbe ChristophersonBobbe Christopherson

Chemical Weathering ProcessesChemical Weathering Processes

ReductionReduction - - reverse of oxidation, caused reverse of oxidation, caused by the addition of one or more electrons to by the addition of one or more electrons to a metallic element producing a more a metallic element producing a more stable compound. stable compound.

Chemical Weathering ProcessesChemical Weathering Processes HydrationHydration - rigid attachment of H - rigid attachment of H++ and OH and OH-- ionsions to a to a

reacted compound.reacted compound.

HH++ and OH and OH-- ions may become a structural part of the ions may become a structural part of the crystal lattice of the mineral.crystal lattice of the mineral.

Promotes other decomposition reactions by expanding Promotes other decomposition reactions by expanding the crystal lattice offering more surface area for reaction.the crystal lattice offering more surface area for reaction.

Ex.:Ex.:CaSOCaSO44 + 2H + 2H22O O CaSO CaSO44•2H•2H22OOAnhydrite water rxn gypsumAnhydrite water rxn gypsum

Chemical Weathering ProcessesChemical Weathering Processes CarbonationCarbonation - the reaction of carbonate and - the reaction of carbonate and

bicarbonate ions with minerals, especially in a high-CObicarbonate ions with minerals, especially in a high-CO22 environment.environment.

Forms carbonic acid - a product of carbon dioxide and Forms carbonic acid - a product of carbon dioxide and water - is important in solution of carbonates and the water - is important in solution of carbonates and the decomposition of mineral surfaces because of its acidic decomposition of mineral surfaces because of its acidic nature.nature.

Ex.:Ex.:

HH22O + COO + CO2 2 H H22COCO33 H H++ + HCO + HCO33

--

water carbon dioxidewater carbon dioxide carbonic acid hydronium ion carbonic acid hydronium ion bicarbonate bicarbonate

Chemical Weathering ProcessesChemical Weathering Processes

Solution is the dissolving of a mineral by water Solution is the dissolving of a mineral by water and the ions it carries as it moves through and and the ions it carries as it moves through and around rocks and minerals.around rocks and minerals.

most effective in areas that have humid and hot most effective in areas that have humid and hot climates.climates.

Examples of common, easily dissolved minerals:Examples of common, easily dissolved minerals:

halite (NaCl - salt) halite (NaCl - salt) calcite (CaCOcalcite (CaCO33) from limestone) from limestone

Chemical Weathering ProcessesChemical Weathering Processes

Climate is the most important factor Climate is the most important factor affecting all of the above-mentioned affecting all of the above-mentioned chemical weathering processes:chemical weathering processes:

Regulates moisture and temperatureRegulates moisture and temperature

Tropical weathering rates, where T and Tropical weathering rates, where T and moisture are at max. = three and a half times moisture are at max. = three and a half times higher than rates in temperate environments.higher than rates in temperate environments.

Chemical Weathering ProcessesChemical Weathering Processes Chemical Weathering processes act on the joints in granite to dissolve Chemical Weathering processes act on the joints in granite to dissolve

weaker minerals, leading to a rounding of the edges of fracturesweaker minerals, leading to a rounding of the edges of fractures

Bobbe ChristophersonBobbe Christopherson

Chemical Weathering ProcessesChemical Weathering Processes Rounded granite boulder showing spheroidal weathering and disintegration Rounded granite boulder showing spheroidal weathering and disintegration

of rockof rock

Bobbe ChristophersonBobbe Christopherson

Chemical Weathering ProcessesChemical Weathering Processes Spheroidal weathering in the rugged Alabama Hills, CA (note Mt. Whitney in Spheroidal weathering in the rugged Alabama Hills, CA (note Mt. Whitney in

background)background)

Bobbe ChristophersonBobbe Christopherson

Biological Weathering ProcessesBiological Weathering ProcessesBiological WeatheringBiological Weathering – due to the activity of an organism. – due to the activity of an organism.

Types range from bacteria to plants to animals.Types range from bacteria to plants to animals.

Biological weathering can be either chemical or physical in Biological weathering can be either chemical or physical in character.character.

Some of the more important processes are:Some of the more important processes are:

Fracture by consumption, burrowing, or root growth;Fracture by consumption, burrowing, or root growth;

Movement and mixing causing different physical and/or chemical Movement and mixing causing different physical and/or chemical conditions;conditions;

Respiration – can produce CO2 Respiration – can produce CO2 carbonic acid carbonic acid Solution Solution

Biological Weathering ProcessesBiological Weathering Processes More biological weathering processes:More biological weathering processes:

ChelationChelation – organisms produce organic chelates that decompose – organisms produce organic chelates that decompose minerals and rocks by the removing of metallic minerals and rocks by the removing of metallic cationscations;;

Organisms can influence the moisture regime in soils and enhance Organisms can influence the moisture regime in soils and enhance weathering. Shade, root masses, and weathering. Shade, root masses, and humushumus all act to increase the all act to increase the availability of water in the soil profile. Water is a necessary component availability of water in the soil profile. Water is a necessary component in several physical and chemical weathering processes.in several physical and chemical weathering processes.

Organisms can influence the Organisms can influence the pHpH of the soil leading to solution: of the soil leading to solution:

Roots can release CORoots can release CO22 leading to carbonic acid formation, lowering the pH; leading to carbonic acid formation, lowering the pH;

Cation exchangeCation exchange reactions, in which plants exchange reactions, in which plants exchange basic cationsbasic cations for for hydrogen ions, can lower soil pH by increasing Hhydrogen ions, can lower soil pH by increasing H++ concentration. concentration.

Biological Weathering ProcessesBiological Weathering Processes

Tree roots growing in and on fractures in bedrockTree roots growing in and on fractures in bedrock

Robert W. ChristophersonRobert W. Christopherson

Biological Weathering ProcessesBiological Weathering Processes

Roots can exert tremendous force on sides of rock jointsRoots can exert tremendous force on sides of rock joints

Robert W. ChristophersonRobert W. Christopherson

Biological Weathering ProcessesBiological Weathering ProcessesLichens helping to disintegrate ropy “pahoehoe” basalt lava in Iceland. Basaltic Lichens helping to disintegrate ropy “pahoehoe” basalt lava in Iceland. Basaltic

lava is less resistant to weathering than granite (inset shows surrounding, lava is less resistant to weathering than granite (inset shows surrounding, moist landscape)moist landscape)

Robert W. ChristophersonRobert W. Christopherson