We Stand Somewhere Between The Mountain

And The AntOnondaga

Weathering Processes

Danny M. Vaughn, Ph.D., CMS  • Weathering – The breakdown of Earth materials.- Physical (mechanical or disintegration) weathering processes.- Chemical (decomposition, resulting in a chemical change) weathering processes.  

• Erosion – transport of weathered materials by water, wind, and/or ice.Geomorphic agents of erosion: • Fluvial (movement of particles by channelized flow). • Glacial (movement of particles by ice). • Littoral (movement of particles along the ocean/land interface). • Aeolian (movement of particles by wind).

Factors Influencing Weathering• Joints – fractures in bedrock w/out displacement.• Increases surface area which enhances weathering.• Climate factors – precipitation, temperature, &freeze-thaw.• Soil water.• Ground water.• Rock composition.• Rock structure.• Slope angle & orientation.• Vegetation.• Microscopic boundary conditions.• Time.

Surface Area

• Physical weathering along joints – Canyonlands N.P., Utah.

If You See No Reason For Giving Thanks,

The Fault Lies In Yourself.Minquass

• Minerals melt & solidify at ~ the same temperature.• Minerals that melt first crystallize last.• Minerals that melt last crystallize first.• Process relates silicate mineral crystallization tomagma composition.

(Anorthite)

(Albite)

(Orthoclase)

(Hornblende)

How does an under-standing for Bowen’sReaction Series relate to weathering processes?

Weathering & Bowen’s Reaction Series

• Arid climates draw moisture to the surface.

• Evaporation leaves mineral traces.

• Crystal growth in cracks enhance pressure breaking apart the rock.

• Hydration may form minerals (gypsum) that expand & weaken a joint.

Hydration

Mechanical Weathering

• Frost wedging

• Salt wedging• Thermal

expansion & contraction

• Mechanical exfoliation

• Root penetration

• Abrasion

Physical Weathering

Frost shattering of granite.

Frost action (Talus) in an alpine environment.

Talus slopes at the base of a mountain.

Mechanical Weathering

• Frost wedging• Salt wedging• Thermal

expansion & Contraction

• Mechanical exfoliation

• Root penetration• Abrasion

Mechanical Weathering

• Frost wedging• Salt wedging• Thermal

expansion & contraction

• Mechanical exfoliation

• Root penetration• Abrasion

Exfoliation (Unloading) in Granite

Pressure isreleased whenoverburden isremoved.

Mechanical WeatheringFormation of Mechanical

Exfoliation

Mechanical Weathering

• Frost wedging• Salt wedging• Thermal

expansion & contraction

• Mechanical exfoliation

• Root penetration

• Abrasion

Mechanical Weathering

• Frost wedging• Salt wedging• Thermal expansion

& contraction• Mechanical

exfoliation• Root penetration• Abrasion

Differential weathering in sandstone & shale.

Acidic

Alkaline

Neutral

Chemical Weathering:The process of decomposition by the chemical breakdown of Earth materials.pH – a measure of the

hydrogen ion concentration in a solution.

Chemical Terms Solvent - a fluid capable of dissolving a substance. Solute - a material dissolved in solution. Solution - combined solvent and solute. Solubility - the quantity of solute capable of being dissolved in solution. Dilute - a solution having a greater amount of solvent than solute. Concentrated - a solution having a greater amount of solutethan solvent. Saturated - when the concentration of solute exceeds anequilibrium solution.

Atmospheric Impact on Weathering Processes

Chemical Weathering

• Dissolution

• Hydrolysis

• Oxidation

CaCO3 + H2CO3 --> Ca2+ + 2HCO3

–

Calcite + Carbonic acid Calcium ion Bicarbonate ion

Carbonization – a mineral dissolves into solution.

Chemically Weathering Limestone (CaCO3)• Chemical weathering of carbonate rocks places CaCO3 in solution.

• Solubility of CaCO3 is directly proportional to the amount of CO2 in solution.• Warm water holds less CO2 in solution then cold water.

• It follows, CaCO3 becomes less soluble, thus CaCO3 precipitates out of solution.• Limestone is formed from the deposits.

• In colder water, more CO2 is capable of remaining in solution, thus more CaCO3 is held in solution & less precipitates.

• Agitating water degases CO2 enhancing precipitation of CaCO3.

• Aquatic plants remove CO2, thus also enhancing precipitation of CaCO3.

• Decreasing water pressure (shallow) promotes CO2 degassing also enhancing precipitation of CaCO3.

Karst Topography and Landscapes  

• Karst – Krs Plateau in Yugoslovia.• Carbonate rocks susceptible to chemical weathering. 

• Surface covered w/ sinkholes (depressions).• Caves & subterranean drainage conduits.  

Karst forms require –• 80% carbonate content in limestone or dolostone.

• Well-developed joints.• Humid-sub-humid climate w/ good vegetation cover.

• Aerated zone between surface & water table.

Collapsed Sinkhole in Florida

Karst Features

Chemical Weathering

• Dissolution

• Hydrolysis

• Oxidation

2KAlSi3O8 + 2H+ + 9H2O --> Al2Si2O5(OH)4 + 4H4SiO4 + 2K2+

Potassium Hydrogen ions Kaolinite clay Silicic Potassium feldspar (from water) acid ions

Interlocking crystals breakdown by granular disintegrationin granite.

Chemical Weathering

Decomposition ofEarth materials.

Spheroidal weathering

Granulardisintegration

Chemical Weathering

• Dissolution

• Hydrolysis

• Oxidation

4Fe3+ + 3O2 --> 2Fe2O3Iron Oxygen Hematite

Metallic elementscombine w/ oxygen.

Oxidized sandstones inRed Rock Canyon, NV

Oxidized Utisols inGeorgia. Highly weathered w/ iron & aluminum.

Factors That Influence Chemical

Weathering

• Climate• Living

organisms• Time• Mineral

structure & composition

Factors That Influence Chemical Weathering

• Climate• Living

organisms• Time• Mineral

structure & composition

Factors That Influence Chemical Weathering

• Climate• Living

organisms• Time• Mineral

structure & composition

Products of Chemical Weathering

• Clay minerals• Metal ores• Rounded

boulders

Regolith, Soil, and Parent Materials

Regolith – the upper surface of bedrock exposed to weathering.

What Is Soil?The uppermost, organic-rich portion of the regolith that supports plant growth

A typical soil profile in a temperate mid-western environment.

Factors That Influence

Soil Formation

• Parent material

• Climate• Topography• Biological

activity• Time

Factors That Influence

Soil Formation

• Parent material

• Climate• Topography• Biological

activity• Time

Factors That Influence Soil Formation

• Parent material• Climate• Topography• Biological

activity• Time

Transfer of Nutrients through Upper Horizons

Caliche

Transported Minerals in Arid & Semi-arid Environments

Soil Classificatio

n

Soil Classification

Table 5-1

PaleosolsOld, Buried

Soils

Interconnectiveness of Earth Systems