Mechanical and Chemical Weathering

Mechanical Weathering

• Root Wedging: Plant roots can grow into cracks in rocks, causing them to split apart.
• Frost Wedging: Occurs when water seeps into cracks, freezes and expands, putting pressure on the rock.
• Salt Expansion: Salt crystals grow in spaces within rocks, exerting pressure and causing them to break.
• Tafoni: Series of holes in rocks, often a result of salt expansion.
• Hopper Crystals: Square imprints left behind in soft sediments after salt water evaporates.

Chemical Weathering

• The dominant weathering process in humid, warm environments.
• Chemical reactions break down rocks, creating soluble ions.
• Temperature accelerates chemical weathering.
• Surface-area-to-volume Ratio: Mechanical weathering creates more surface area for chemical weathering.

Carbonic Acid and Hydrolysis

• Carbonic Acid: Forms when CO2 dissolves in water, making precipitation slightly acidic.
• Hydrolysis: Water molecules interact with minerals, replacing mineral cations and forming clay minerals.
• Feldspar Hydrolysis: Creates clay minerals, metal cations, bicarbonate anions, and silica.

Dissolution

• Dissolution: Minerals dissolve in water.
• Salt and Calcite: Are prone to dissolution.
• Acidic Water: Dissolves rocks at a higher rate due to presence of H+ ions.
• Lichen and Bacteria: Release organic acids that enhance dissolution.

Oxidation

• Rust: Forms when iron atoms bond with oxygen.
• Iron Oxides: Can permeate rocks, form coatings, or create hollows.
• Hematite, Goethite, Limontite: Common iron oxides produced through oxidation.
• Cementation: Iron oxides bind mineral grains together in sedimentary rocks.
• Iron Concretions: Occur when resistant minerals replace existing minerals in bedrock.

Erosion

• Mechanical Process: Removal of weathered sediment by water, gravity, wind, or ice.
• Erosional Resistance: Creates distinctive geological features, like Grand Canyon cliffs.
• Hoodoo: A distinctive geological feature created by different erosion rates.

Soil

• Formed by weathering of bedrock and the interaction of organisms.
• Humus: Organic matter in soil.
• Soil Horizons: Distinct layers within soil profiles.
• O Horizon: Primarily organic material.
• A Horizon: Topsoil, a mix of humus and mineral sediment.
• B Horizon: Subsoil, with weathered sediment and some humus.
• C Horizon: Substratum, containing physically broken bedrock.
• R Horizon: Unweathered parent bedrock.
• Soil Orders: USDA classification system for soil types.
• Xoxisols: Found in tropical regions, contain bauxite.
• Ardisols: Form in dry climates, with hardened calcite layers (caliche).
• Andisols: Develop from volcanic ash deposits.
• Alfisols: Contain silicate clay minerals, highly productive for farming.

Sedimentary Rocks

• Divided into clastic and chemical categories.

This quiz explores the concepts of mechanical and chemical weathering, detailing processes like root wedging, frost wedging, and the effects of carbonic acid. Understand how different environmental factors influence weathering and rock breakdown. Test your knowledge on the mechanisms that shape our Earth's landscape.