Weathering, Soil, and Unstable Slopes

Vocabulary flashcards for geology lecture notes on Weathering, Soil, and Unstable Slopes (sections 15.1 to 15.3).

Weathering

The breakdown and alteration of Earth materials at the surface.

Physical weathering

Mechanical breakdown of rocks without changing their chemistry.

Chemical weathering

Breakdown involving chemical reactions that change mineral structure.

Joints

Natural fractures or cracks in rock with no significant movement.

Expansion joints

Fractures formed as rocks cool or are uplifted, releasing pressure.

Exfoliation

Peeling off of curved rock layers due to pressure release.

Talus

Accumulation of angular rock debris at the base of a slope.

Surface area

Total area exposed to weathering; increases with fracturing.

Frost wedging

Expansion of frozen water in cracks that breaks rocks apart.

Thermal expansion

Expansion and contraction of minerals due to temperature changes.

Root wedging

Roots growing into cracks and widening them.

Mineral wedging

Growth of minerals (like salt) in cracks, forcing them open.

Burrowing

Activity of organisms that exposes materials to surface weathering.

Chemical weathering

Decomposition of rocks via chemical reactions (mainly involving water).

Dissolution

Process of minerals dissolving in water or weak acids.

Carbonic acid (H₂CO₃)

Weak acid formed when CO₂ dissolves in water; key in dissolution.

Calcite (CaCO₃)

Main mineral in limestone, dissolves easily in acidic water.

Bicarbonate (HCO₃⁻)

Ion produced when calcite dissolves; found in water.

Oxidation

Chemical reaction where a mineral (especially iron-bearing) reacts with oxygen.

Hematite (Fe₂O₃)

Reddish iron oxide mineral formed during oxidation.

Hydrolysis

Chemical reaction where minerals react with water to form clay.

K-feldspar (Potassium feldspar)

A common mineral that breaks down to form kaolinite clay.

Kaolinite

A type of clay mineral formed through hydrolysis of feldspar.

Cations

Positively charged ions (e.g., K⁺, Na⁺, Ca²⁺) released during chemical weathering.

Salinity

Salt content of water; affected by weathering and evaporation.

Evaporation

Process that concentrates salts in oceans as water turns to vapor.

Parent material

Original rock from which weathering products are derived.

Mineral stability

Resistance of a mineral to weathering under surface conditions.

Bowen’s Reaction Series

Sequence describing mineral crystallization order and stability.

Mafic minerals

Dark, magnesium- and iron-rich minerals (e.g., olivine, pyroxene); less stable.

Quartz

Very stable, resistant mineral; commonly forms sand.

Feldspar

Abundant mineral in granite; weathers to clay.

Clay minerals

Fine-grained minerals formed by chemical weathering.

Dissolved ions

Weathering products carried by water (e.g., Na⁺, Ca²⁺).

Solubility

Ability of a substance to dissolve in water; affects chemical weathering.

Rock composition

Types and proportions of minerals within a rock.

Discontinuities

Weaknesses in rock (e.g., joints, fractures) that affect weathering rates.

Granite

Igneous rock rich in quartz and feldspar; weathers into sand and clay.

Quartz sand

Product of physically weathered quartz; found in dunes and beaches