Weathering, Erosion, Transportation, and Deposition....What is the difference between them?
 

Weathering is the physical disintegration or chemical decomposition of rock and minerals at the earth's surface. Note that weathering is different from erosion. Erosion is the physical removal of rock particles. Weathering involves breakdown or altering of rocks-this takes time and the type of weathering depends on the type of rock and climate.
 

Mechanical (Physical) Weathering--- Most common in cold climates --Breaking down of rocks into smaller pieces
 

Frost Action

Frost Wedging-- most effective agent of mechanical weakening

Frost Heaving -- can break up rock surfaces

Salt action

Abrasion- - friction-agents of erosion, H₂O-Runs, Wears; Wind; Glacier

Pressure Release - Uplift and erosion

Unloading -- Leads to cracks "sheet joints" to outer surface of rock

Exfoliation -- Sparking off of rock layers

Exfoliation Dome

Plant growth (organic activity)

Burrowing animals

Extreme changes in temperature (thermal)
 

Chemical weathering - Rock decomposition

Why do we have chemical weathering?

Concept of equilibrium or balance
 

Types of chemical weathering

Oxidation - (Chemical reaction in which ion or element loses electrons)

Rusting of iron 4Fe + 30₂ 2Fe₂O₃ Hematite

Brick red color when powdered

When it is hydrated, Fe₂O₃ in H₂O - limonite yellowish brown

Iron pyroxene 4FeSiO₃ + O₂ 2Fe₂O₃ (hematite) + Silica 4SiO₄ (Dissolved )
 

Acid - Most effective agent of chemical weathering

H⁺ being substituted for other ions such as Ca²⁺, Na⁺ or K⁺ within minerals

Sulfuric acid, hydrofluoric acid

S + O₂ SO₂

2SO₂ + 2H₂O + O₂ 2H₂SO₄

CO₂ + H₂O H₂CO₃ H⁺ + HCO₃

Solution weathering

Carbonic acid on limestone

CaCO₃ + H⁺ + HCO₃ Ca²⁺ + 2HCO₃

Caves, caverns, sinkholes

Hydrolysis

Feldspar (orthoclase)

KAlSi₃O₂ + 2H⁺ + 2HCO₃ + H₂O Al₂Si₂O₅(OH)₄

or

(KAlSi₃O₈ + H₂O Al₂Si₂O₅(OH)₄ (Kaolinite)
 

Weathering of feldspar is much slower than that of calcite weathering

+ 2K⁺ + 2HCO₃ + 4SiO₂

Other minerals such as Muscovite weathers to clay mineral

2KAl₃O₈ + 2H₂CO₃ + H₂O Al₂S₂O₅(OH)₄ + 4SiO₂ + 2K⁺ + 2HCO₃
 

Bauxite - aluminum oxide
 

Major factors controlling rates of weathering

1. Mineral stability

2. Rainfall

3. Temperature

4. Vegetation & other life forms

5. Soil cover

Surface area problem 1x1x1 (6m³ ) cube divided into 8 fragments of 0.5m sides (12 m³ )

Oxidation

Carbonic acid (dissolution carbonates)

Hydrolysis - has control or reacts a mineral

Hydration - addition of water

Feldspar Kaolinite 
ADDITIONAL READING ON SOIL AND WEATHERING SEE PROF P. J. W. GORE WEBSITE
    
Soil
 

Soil means different things to different people

To the Engineer, ...

To the Soil Scientist....
 

Regolith

Loam

Litter

Humus
 

But to the geologist - the weathered unconsolidated material on top of bed rock......

Well developed soils have three distinct layers

O = Zone with decaying vegetation

A = Zone of leaching

B = Zone of accumulation

C = Zone of incompletely weathered parent material

True soil is made up of O, A, & B. True soil is also known as SOLUM

Soil nutrients - Phosphorous, nitrogen, and potassium
 

S = f(CROP)T²

C = Climate (most important factor)

Pedalfer (Al and Fe) Humid Region; Pedocals (calcite) - Arid Climate

R = Relief

O = Organic

P = Parent material - Transplanted; Residual
 

Hardpan Land layer e.g. caliche

Laterite - tropical regions... Iron & Al oxides mostly

Bauxtite
 

Salinization
 

Three Major Soil Groups

Pedalfers - rich in Al and Fe oxides & hydroxides - Moderate to high rainfall; Grd apic hard (Temperate)

Pedocal - rich in Ca - warm dry area SW USA

Laterite - dipped soil

Paleosols
 

Soil Orders

Andisols - Volcanic Ash

Entisols - Young soil

Inceptisols - A horizon

Matured

Molisols - semi-arid organic A/B calcium

Alfisols - Thin A

Spodosols- Leaching of A - most climates

Aridsols

Vertisols - High clay content - Equatorial/Tropical

Oxisols - Very old

Ultisols - highly weathered? Tropical to subtropical climates

Histosols- wet and organic rich

For a more complete description of weathering and soil see weathering lab from Georgia Perimeter College. This will help you in your understanding of weathering and soil/sediments and sedimentary rocks.