Chapter 5 Weathering and Soil

These flashcards cover key vocabulary related to weathering and soil processes, definitions of important concepts, and classifications that are essential for understanding the topic.

Weathering

The group of destructive processes that change the physical and chemical character of rocks at or near the Earth's surface.

Types of Weathering

Physical and Chemical

Erosion

The physical picking up of rock particles by water, ice, or wind.

Transportation

The movement of eroded particles by water, ice, or wind.

Physical Weathering

Processes that break rocks into smaller pieces without changes to the chemical composition.

Chemical Weathering

Decomposition of rock from exposure to water and atmospheric gases.

Effects of Weathering

Destruction of building materials

Discoloration of surface outcrops

Production of soil

Impacts the atmosphere

» Removes carbon dioxide

Creates interesting and unusual rock

shapes

» Spheroidal

» Differential

Frost Wedging

A mechanical weathering process where water freezes and expands in rock cracks, causing further breakdown.

Spheroidal Weathering

A type of weathering that occurs where rock has been rounded by the weathering process, typically more at corners than edges.

Differential Weathering

The process where different rocks weather at different rates due to their composition.

Mechanical Weathering: Pressure Release

Breaks into smaller and smaller pieces, each retaining the

characteristic of the original material

In nature 4 main physical processes lead to the fragmentation of rocks:

» Pressure release

or jointing & Sheeting

» Frost wedging

» Salt crystal growth

» Biological activity

Pressure release or jointing & Sheeting

A mechanical weathering process where the outer layers of rock are stripped away due to a decrease in pressure, often leading to the formation of cracks and joints.

Frost Action

Salt crystal growth

A mechanical weathering process where saltwater infiltrates cracks in rocks, and as the water evaporates, salt crystals form and expand, exerting pressure on the surrounding rock.

Biological activity

A mechanical weathering process where organisms such as plants, animals, and microorganisms break down rocks through physical and chemical means, often leading to soil formation.

Processes of Chemical Weathering

• Dissolution

• Oxidation

• Hydrolysis

Dissolution

A chemical weathering process where minerals are dissolved in water, often resulting in the formation of solution features such as sinkholes and limestone caves.

Oxidation

Hydrolysis

Role of  Acids 

Climate

Rock Composition

Slope

Feldspar Main Soild Product

a common mineral in igneous rocks, it is a key component of granite and can weather to clay minerals.

Ferromagnesian Main Soild Product

a common mineral in igneous rocks, it is a key component of granite and can weather to clay minerals.

Soil

A layer of weathered, unconsolidated material on top of bedrock capable of supporting plant growth.

Soil Horizons

Layers within the soil profile that consist of different materials and characteristics.

Pedon

The smallest 3-D unit that represents the entire soil body.

Polypedon

A group of pedons which represents a specific soil type in a given area.

Horizonation

The formation of soil horizons through various processes occurring over time.

How many soil layers are there 

in an ideal soil profile, typically between three and five layers, known as horizons.

Soil Horizons

O horizon – uppermost layer; organic material

A horizon – dark-colored, rich in organic matter and high in biological activity

E horizon – zone of leaching; fine-grained material removed by percolating water

B horizon – zone of accumulation; clays and iron oxides leached down from above; formation of

hard pan in wet climates

C horizon – partially weathered bedrock

Tops Soil includes

the O and A horizons, containing organic matter and nutrients essential for plant growth.

Subsoil includes

the E and B horizon, which contains accumulated minerals and nutrients, but less organic matter compared to topsoil.

Bedrock includes

the C horizon, consisting of unweathered rock that serves as the foundation for soil layers above.

Factors of Soil formation

1. Parent material (PM)

2. Climate: rainfall & temperature result in

weathering

3. Living organisms (Specifically

Vegetation and Human activity)

4. Topography or slope

5. Time

Carbonic Acid

An acid formed when carbon dioxide combines with water, important in weathering.

Ultisols

Highly weathered soils low in nutrients, typically found in humid, tropical climates.

Aridisols

Soils formed in dry climates, often containing high levels of salts.

Mollisols

Rich, dark soils formed in grassland settings, known for high organic matter.

Oxisols

Soils that are highly weathered, rich in iron and aluminum oxides, usually found in tropical environments.

Soil Erosion

The process by which soil particles are worn away and removed from the landscape, often by water and wind.

Soil Formation Factors

The interaction between parent material, climate, organisms, topography, and time that influences soil development.

Parent material

A. Texture and structure

» B. Chemical and Mineralogical Composition

» PM includes glacial deposits, alluvial and marine

deposits, residual minerals and rocks (bedrock), etc

Climate 

rainfall & temperature result in weathering

Living organisms (Specifically

Vegetation and Human activity)

The type of vegetation affects the soil

color and organic matter content,

especially in the A (or top) horizon

»Trees contribute less organic matter to the

soil each year when compared to

grasslands

Topography

Refers to the landscape's surface features, including slope and elevation, which influence soil formation and weathering processes.

Elevation

the height above mean sea level

Slope 

the tilt or inclination of the land

Aspect 

the direction the slope is facing

Time

Time is important in soil formation

because it determine the degree to which

the other soil forming factors express

Biological Weathering

Weathering that occurs due to natural processes from plants and animals.

Chemical Weathering Processes

Includes dissolution, oxidation, and hydrolysis, leading to the breakdown of rock components.

Hardpans

Layers of soil that are very hard and prevent water and roots from penetrating.

Soil Texture Triangle

A triangular diagram that shows the proportion of sand, silt, and clay in soil.

Granular Soil

Soil composed of small, crumbly particles, typically found in the surface horizon.

Old Soil

Young Soil

Soil Classification System

A hierarchical system that categorizes soil based on its characteristics and horizons.

Soil Particals by size

are categorized into sand, silt, and clay based on their diameter, influencing soil texture and behavior.

Soil is made up of

20-30 air

20-30 water

5 organic

45 minerals

Loam

is a fertile soil type composed of a balanced mixture of sand, silt, and clay, ideal for agriculture.

Pressure release

is a geological process that occurs when overlying materials are removed, allowing underlying rocks to expand and fracture, leading to mechanical weathering.

Residual soil

that remains in place due to the weathering of the underlying bedrock, typically reflecting the composition of that rock.

Sheet Joints

are fractures that form parallel to the rock surface due to pressure release, allowing rocks to peel or flake away.

Transported Soil

is soil that has been moved from its original location, often by water, wind, or ice, and typically differs in composition from the bedrock below.

Frost Heaving

is a process that occurs when water in the soil freezes, expands, and causes the soil to lift or heave, which can disrupt the surface and structures above.

Frost Action

refers to the mechanical weathering process in which repeated freezing and thawing of water in soil or rock causes physical breakdown. This cyclical action can result in the disintegration of materials over time.

Exfoliation Dome

is a geological formation created by the process of exfoliation, where layers of rock peel away due to thermal expansion and contraction, often resulting in rounded, dome-like shapes in mountainous regions.

Exfoliation

is the process in which outer layers of rock are removed or flaked off due to weathering effects such as temperature changes or physical stress.

Hematite

is an iron oxide mineral commonly found in sedimentary rocks. It is a major ore of iron and is known for its reddish color, which is due to its high iron content.

limonite

is a mineral composed of iron oxide hydroxides and is often found in soils and sedimentary rocks. It typically appears in yellowish to brown colors and serves as an important ore of iron.