Physical Geology Ch 6- Weathering, Erosion, and Soil

Spheroidal Weathering

When a stone (rectangular) weathers into a more spherical shape because this is the most stable shape it can assume. The corners and edges of rocks are the first to break and be shaped.

Oxidation

When one or more metallic elements such as iron (Fe) reacts with oxygen to form an oxide.

Another example of oxidation is:

When pyrite (FeS2) oxidizes to form sulfuric acid (H2SO4) and iron oxide. This can be a serious environmental hazard in coal-mining areas due to the chance acidic water and souls can be formed. Example= Lignite Mines in Choctaw County.

Salt Crystal Growth

When the growth of crystals cause the widening of cracks and crevices. Formation of salt crystals is a chemical process and the widening of cracks is a mechanical weathering process.

Hydrolysis continued...

When this reaction takes place in material rich in hydrogen you get acid and when the material is (OH-) you get bases. This process takes place in most non-metallic minerals and rocks such as the Feldspars.

Soil erosion

Wind and running water.

Erosion can be accomplished by:

Wind, glaciers, waves, and marine current.

Crop rotation

Yearly rotation of soil depleting crops and soil enrichment crops.

Strip cropping

growing of different crops on alternate, parallel strips of ground to minimize wind and water erosion. (For example: corn and alfalfa)

Factors that influence soil formation:

All soils form from chemical and mechanical weathering but soils differ in color, texture, thickness, and fertility.

Horizon A

Also called topsoil, contains more organic matter than horizons B and C which are below. There is intense biological activity in this horizon due to plant roots, bacteria, fungi, and animals. Water percolating down through horizon A dissolves soluble minerals and carries them down into the lower horizons B and C by a process called leaching therefore this horizon is called a zone of leaching.

Water and carbon dioxide combine to form different rock types.

An example of this is when limestone is dissolved to create caves.

Soil Degradation:

Any situation where soul loss exceeds soil formation is alarming.

Factors that influence soil formation

A. Climate: the single most important factor influencing soil type and depth.

Root wedging

Biological activity, roots from plants can split rocks into smaller particles.

Organisms

Burrowing animals such as worms, termites, etc. constantly mix soul and sediment particles.

Climate

Chemical processes proceed more rapidly at high temperatures and in the presence of liquids. Therefore, there is more chemical weathering in the tropics than in arid or artic regions. Vegetation and animal life are much more abundant in the tropics.

Hydrolysis

Chemical reaction between Hydrogen and hydroxyl ions in water. This reaction takes placd when water (H2O) is dissociated into (H+) and (OH-) ions.

Physical deterioration

Compaction from mankind, clear cutting, etc.

Terracing

Flat areas on slope ground.

Pedocals

Found in arid and semiarid western US. Soils contain less organic matter so the soil is lighter in color and contains more unstable minerals due to less chemical weathering.

Pedalfers

Found in humid regions such as eastern US and much of Canada. The name derived from the Greek word "pedon" meaning "soil" and drink the chemical symbols for aluminum (Al) and iron (Fe). Due to soil being formed where there us abundant moisture most soluble minerals have been leached out of Horizon A.

Sheet Joints

Fractures that form due to the pressure released when overlying rocks are eroded.

Pressure Release

Mechanical weathering process evident in rocks that formed as deeply buried intrusive igneous bodies such as batholiths.

Laterite

Soil formed in the tropics where chemical weathering is intense and leaching of soluble minerals is complete. These soils are red in color and extend to depths of tens of meters.

This can be cause by:

Soil erosion, chemical deterioration, and physical deterioration.

The rate of chemical weathering is

Increased with more surface area of rock material. Mechanical weathering increases this surface area by breaking rocks into smaller particles which exposes more of the rock therefore increasing chemical weathering.

Frost Action/Frost Wedging:

Involves repeated freezing and thawing of water in cracks. This will cause expansion of these cracks causing blocks of material to be pried loose. The debris that is formed is called Talus.

Solution

Ions of a substance separate in a liquid and the solid substance dissolves. Water is a very good solvent because it's molecules have an asymmetrical shape that makes it easy for soluble substances such as NaCl to be attracted and dissolved into a solution.

4Fe + 3O2= 2Fe2O3

Iron oxide or hematite is 2Fe2O3. This is how iron rusts.

Water

Is the difference between frost action/frost wedging and thermal expansion and contraction.

Another factor that experiences soil formation:

Lay of Land-relief/slope slope=rise over run

Chemical deterioration

Nutrients depleted, insufficient use of fertilizer, pollution.

Horizon O

Only a few centimeters thick and consists of organic matter.

Another factor that influences soil formation:

Parent Material

No-till planting

Plant seeds without plowing

Windbreaks

Plant trees to break wind

Contour plowing

Plowing perpendicular to the slope- do this instead of parallel.

Rate of chemical weathering:

Several variables control the rate of chemical weathering.

Exfoliation

Slabs of rock bounded by sheet joints may slip, slide, or break off of the host or parent rock and accumulate as talus. This results in large rounded domes known as exfoliation domes. Example= Stone Mountain, Georgia.

Parent Material

Some rocks are more resistant than others to chemical processes. Table 6.1 shows that the metallic silicates that were formed by less heat and pressure are more stable than the ones produced under high heat pressure environments. Non-metallics also adhere to this pattern.

Horizon B

Subsoil, contains fewer organisms. Known as zone of accumulation because soluble minerals leached from horizon A accumulate in horizon B.

Thermal Expansion and Contraction

The constant heating and cooling of rocks can cause fractures. Example=desert slum aye where the range in temp. is 30 degrees Celsius.

Horizon C

The lowest soil layer, consists of partially altered parent material that grades into unaltered parent material and very little organic matter.

Weathering

The physical breakdown and chemical alteration of rocks and minerals at or near Earth's surface.

Chemical Weathering

The process in which rock material is altered by a chemical process.

Erosion

The removal of weathered material from parent rock is known as

Soils

The soil can be looked at in a vertical cross section and be seen to have distinct layers. These layers are also known as soil horizons. These horizons differ in texture, structure, composition, and color. The boundaries between these layers are gradual and not sharp.

Soil conservation

This can be achieved by: terracing, strip cropping, crop rotation, contour plowing, no till planting, and windbreaks.

Machanical Weathering

This takes place when physical forces break down Earth materials into smaller pieces.

Another factor that influences soil formation:

Time- the more time, the more weathering, erosion, transportation, deposition, etc.

Another Factor that influences soil formation:

Type of organism