Chapter 2 - Weathering, Erosion and Soil Formation

Types of rocks

Igneous

Metamorphic

Sedimentary

Igneous

Formed by volcanic forces such as molten magma

Comprised of primary minerals such as feldspars, and are generally dark-colored mineral that contain iron and magnesium

More easily weathered than other types of rocks

Ex. granite, diorite

Sedimentary rocks

Formed by the compressing or cementing of preexisting, older rocks

Varying resistance to weathering based upon dominant minerals and cementing agent

Ex, Sandstone, Shale

Metamorphic rocks

Formed by metamorphism or change in form of other rocks (shifting of tectonic plates)

Ex. Marble, slate

Weathering

The physical breakdown and chemical alteration of rock at or near the Earth's surface

-Breaks rocks down into smaller materials and releases soluble materials and synthesizing new materials

Types of physical weathering (Disintegration)

-thermal stress

-plants/animals

-wetting/drying

-freezing/thawing

-Abrasion by wind/water/ice

Physical weathering - temperature

changes causing rocks to crack or break apart due to expansion and contraction

Process may be accelerated with formation of ice in surface cracks

Exfoliation

Physical weathering process where outer layers of rock peel away

Physical weathering - Abrasion by water/ice/wind

-rounding of rock in river

-Ocean turning rocks into sand

-Windblown sand wearing down rocks

-Glacial ice masses grinding down on rocks

Physical weathering - Plants and animals

Roots cracking/prying apart rocks

Burrowing animals disintegrating rocks

Types of Biochemical weathering

• Oxidation-Reduction

• Carbonation

• Hydrolysis

• Hydration

• Dissolution

• ComplexationProcesses that alter minerals through chemical reactions involving biological activity, resulting in the breakdown of rocks.

Biochemical weathering - Oxidation-Reducation

Exposed to air in water during soil formation resulting in the loss of an electron

-Chemical reactions in which a compound like iron loses electrons

Biochemical weathering -

interaction between organic compounds and minerals leading to the breakdown or alteration of mineralsthrough chemical reactions that involve biological activity.

Biochemical weathering - Hydration

intact water molecules bind to a mineral resulting in changes to its physical and chemical properties.

Biochemical weathering - Hydrolysis

water molecules split into hydrogen and hydroxyl components and hydrogen replaces a cation in mineral structure

Biochemical weathering - Dissolution

water hydrates the cations and anions until they become dissociated from each other and surrounded by water molecules

Biochemical weathering - Carbonation

Carbon dioxide dissolves in water forming carbonic acid, which reacts with minerals and facilitates their weathering.

Main Factors influencing soil formation

• Parent materials

• climate

• biota

• topography

• time

Main factors influencing soil formation - Climate

Most influential factor in soil formation

Determines nature/intensity of weathering over large areas

Main factors influencing soil formation - Biota (living organisms)

• Vegetation reduces soil erosion by cover

• Organic acids from plants can convert certain minerals into available forms for other plants

Main factors influencing soil formation - Topography

Elevation - affects biota

Slope - steeper slopes lead to erosion and movement downwards

aspect - soil moisture is lower on south aspects

Main factors influencing soil formation - Parent Material

Igneous rocks
Sedimentary rocks
Metamorphic rocks
Glacial deposits
Water deposits (riverine, lacustrine,
alluvium)
Wind deposits – sand dunes, loess

Main factors influencing soil formation - Time

Measured from when plants begin to grow on surface of land

-Weathering process

-Human inputs of silt removal of organic material

Residual parent material

Develops in place from weathering of underlying rock

Colluvial debris (colluvium)

poorly sorted rock fragments detached from heights above and carried downslope assisted by gravitythat accumulates at the base of hills or slopes.

Types of alluvial stream deposits

Floodplains

Alluvial fans

Deltas

Floodplains

Sediment carried by stream during flood event,

coarser material deposited in river channel

finer material deposited further from channel

Alluvial fans

Streams that leave a narrow valley and spread out into a larger valley leaving a fan-shaped deposit of sediment.

Deposits finer materials towards the bottom of the fan and coarser materials towards the top.

Delta deposits

Suspended fine material deposited near the mouth of a river

One of the most extensive and biological important wetland habitats

Drift

All material of glacial origin, whether deposited by ice or associated water

Glacial Till

Unsorted debris directly deposited by glaciers, consisting of a mix of clay, silt, sand, gravel, and boulders.

Glacial outwash

Sorted sediments deposited by glacial meltwater, primarily sand and gravel, found in outwash plain

Lacustrine deposits

Formed in glacial lakes

-Coarse delta material and beach deposits near shore

-Fine silts and clay formed in deeper waters and often contain layers of sediment that reflect varying environmental conditions.

Eolian parent material

Wind transported materials

-dune sand

-loess

-aerosolic dust

-volcanic ash

Loess

Windblowd materials primarily composed of silt with very fine sand, coarse clay

Organic deposits

-Peat (fibric)

-Muck (sapric)

Peat (fibric)

A type of organic deposit formed from partially decayed plant material in wetland areas

-Organic residues are sufficiently intact to identify the original plant fibers

Muck (sparic)

A type of organic deposit formed from partially decayed plant material in wetland areas

-Organic residues has little to no original plant fibers

Ablation till

unsorted material deposited directly by glacial ice and showing no stratification

Basal till

Carried in the base of the glacier and commonly laid down under it.

was carried on or near the surface of the glacier and was let down as the glacier melted

Varve

A yearly layer of sediment deposition that typically consists of a light-colored layer of coarse material deposited in spring and a darker layer of fine material deposited in winter.

Fluvial till

glacial sediment that has been reworked or redeposited by river systems.It typically consists of material that has been sorted and layered by the action of flowing water.

Podzol

A type of soil characterized by a leached, acidic layer, typically found in cooler, wetter climates. This soil often displays a distinct color gradient, with a bleached horizon above a darker, mineral-rich layer.

Pedoturbation

The process of mixing and disturbing soil layers by biological activity, such as burrowing animals or plant roots, which affects soil structure and composition.

Four basic processes of soil formation

• Transformations

• Translocations

• additions

• losses

Transformations

Occur when soil components are altered chemically or physically, leading to changes in soil properties.

Translocations

involve the movement of soil materials within the profile, altering the distribution of minerals and organic matter.

Additions

Inputs of materials to the developing soil profile from outside sources

Losses

Materials are lost from the soil profile by:

• leaching into groundwater

• erosion of surface material

• Removal

A horizon development

Commonly first horizon developed

darker in color