Weathering Processes and Types

Weathering

• Weathering is the process by which rocks break down into smaller pieces in place, without movement.
• Three main types of weathering:
  • Mechanical weathering: Breaks down rocks physically without changing their chemistry. Examples:
    • Frost wedging: Water expands in cracks when freezing, fracturing rock.
    • Exfoliation: Rock layers peel off due to pressure release from uplift or erosion.
    • Abrasion: Rocks rubbing against each other.
    • Animal actions: Burrowing animals loosen and break up ground.
    • Plant growth: Roots growing in cracks can wedge and break rocks.
  • Chemical weathering: Changes the chemical makeup of rocks through reactions with water, air, or other substances. Examples:
    • Oxidation: Reaction with oxygen, often leading to rust in iron-rich rocks.
    • Hydrolysis: Reaction with water, breaking down minerals.
    • Carbonation: Reaction with carbon dioxide, dissolving minerals like calcite.
    • Acid rain: Rainwater containing dissolved acids.
  • Biological weathering: Breakdown of rocks by living organisms, often involving chemical reactions. Examples:
    • Plant roots: Roots exert pressure cracking rocks.
    • Lichens: Lichens produce acids that chemically weather rocks.
    • Burrowing animals: Animals loosen and break up rock and soil.

Erosion

• Erosion moves weathered rock and soil from one place to another due to wind, water, ice, or gravity.
• Agents of erosion:
  • Water: Rivers, streams, rain, waves, ocean currents.
  • Wind: Transports smaller particles like sand and dust.
  • Glaciers: Move large amounts of rock and sediment.
  • Gravity: Causes sediment movement downslope, alone or supporting other processes.
• Features of erosion:
  • Valleys: Formed by rivers carving through rock.
  • Canyons: Deep, V-shaped valleys carved by rivers in hard rock.
  • Deltas: Triangular sediment deposits at river mouths.
  • Alluvial fans: Cone-shaped deposits at mountain bases.
• Factors influencing erosion rate:
  • Climate: Rainfall, temperature, and wind speed affect weathering and transport.
  • Topography: Steeper slopes erode faster.
  • Type of rock: Hard rocks erode slower; soft rocks faster.
  • Vegetation: Plants anchor soil, reducing erosion.
• Erosion and Deposition: Erosion moves material; deposition drops it elsewhere. It's a cyclical process, interdependent.
• Sediment Load: Eroded material, characterized by size and composition, is transported.
• Sedimentary rocks: Compressed and cemented sediment forms sedimentary rocks.