Soil Science and Weathering

Vocabulary flashcards covering physical, chemical, and biological weathering, soil composition, horizons, and mass movement.

Physical Weathering

The breakdown of rock into unconnected grains/chunks without changing the original minerals.

Chemical Weathering

Chemical reactions that alter or destroy minerals when in contact with water, altering the molecular structure of rocks and soil.

Biological Weathering

Weakening and breakdown of rocks, minerals, and clays by plants, animals, and microbes.

Frost Wedging (Hydrofracturing)

Water freezing and expanding in joints, widening and extending cracks in rocks.

Haloclasty (Salt Wedging)

Precipitation of salt crystals in open pore spaces, often forming depressions (tafoni).

Thermal Expansion (Insolation Weathering)

Weathering resulting from cycles of heating and cooling of rock.

Abrasion

Mechanical weathering and grinding of rock faces by transported sediment.

Soil

A natural, evolving body which is the product of its environment and contains mineral and organic constituents.

Soil Forming Factors

Parent material, topography/relief, climate, organisms, and time.

Types of Parent Material

Transported, accumulated, and residual materials from which soil is formed.

Soil Horizons

Recognizable layers within a soil profile, each with distinct characteristics.

O Horizon

The uppermost soil layer, rich in organic material, often found in permanently wet environments.

A Horizon

The second soil layer, dark-colored topsoil where organic matter accumulates.

E Horizon

Soil horizon below O or A that has lost clay, iron, or aluminum through weathering and leaching; typically pale colored.

B Horizon

Altered subsoil material with soil structure formation or enrichment in minerals/organic matter; parent material is largely not recognizable.

C Horizon

Weathered parent material, unmodified geological materials or deposits, possibly strongly weathered to clays; can differ from upper layers.

R Horizon

Hard bedrock that is impracticable to dig with a spade.

Soil Composition

Mineral particles (45%), organic matter (5%), soil air (25%), and soil water (25%).

Soil Pedality

Description of the shape, size, and degree of development of peds (soil aggregates).

Irrigation

Maintaining soil moisture content at a level suitable for maximum plant growth.

Drainage

Process that prevents water-logging in soils.

Soil pH Optimum

Optimum soil pH range for most plants and pasture is pH 6-7.

Erosivity

Vulnerability to erosion, controlled by topography, soil characteristics, vegetation cover, and human activities.

LRI Code

Rock type – soil type – slope

_________________________

Erosion – vegetation

Mass Movement

Landslide, mass movement, and mass wasting are all terms used to describe this type of slope process.

Types of Movement (Mass Movement)

Fall, Topple, Slide, Spread, Flow

Falls and Topples

Very common forms of mass movement, particularly on steep cliff faces.

Falls (Mass Movement)

Most of the failed mass travels through the air; movement is extremely rapid.

Topples (Mass Movement)

Involve forward rotation of material out of a cliff face; commonly occur in rocks with vertical joints or bedding.

Planar Slides

Involve movement along an essentially straight shear surface; shallow (< 1-4m).

Debris Avalanche

Extremely rapid shallow flow of partially or fully saturated debris without confinement in an established channel.

Rock Avalanche

Extremely rapid, flow-like movement of broken rock from a large rock slide or fall.