Geological Processes: Exogenic Processes – Quick Notes

EXOGENIC PROCESSES

Exogenic processes are geological processes originating on or above the Earth's surface that shape landforms through weathering, erosion, and deposition.

ENDOGENIC PROCESSES

Endogenic processes originate within the Earth and drive internal geodynamics such as metamorphism, volcanism, and earthquakes.

WEATHERING

Weathering is the disintegration and decomposition of rocks near the Earth's surface due to weather conditions.

  • Types: Physical (mechanical) weathering and Chemical weathering.
  • Weathering produces smaller rock pieces and new minerals/compounds.

PHYSICAL WEATHERING

Physical weathering physically breaks rocks into smaller pieces without changing mineral composition.

  • Key processes: Frost wedging, block disintegration, exfoliation, salt crystal growth, abrasion, and biological activity.
  • Exfoliation: stripping of outer rock layers due to heating.
  • Frost wedging: water in joints freezes and expands, prying rock apart.
  • Block disintegration: heating/cooling cycles cause expansion/contraction.
  • Salt crystal growth: salt crystals exert pressure in pores/cracks.
  • Abrasion: mechanical wearing by collision with particles.
  • Biological activity: organisms disturb and break rocks.

CHEMICAL WEATHERING

Chemical weathering decomposes rocks through chemical reactions that alter minerals.

  • Major processes: Dissolution, Carbonation, Hydrolysis, Oxidation.
  • Dissolution: minerals dissolve in water/acidic solutions (e.g., calcite in limestone).
  • Carbonation: CO₂ + H₂O forms carbonic acid which reacts with minerals.
  • Hydrolysis: minerals react with water (e.g., feldspar to kaolinite).
  • Oxidation: minerals react with oxygen (e.g., iron oxidation to rust).

FACTORS AFFECTING WEATHERING

  • Climate: cold/dry areas favor physical weathering; warm/humid areas favor chemical weathering.
  • Rock type: mineral stability affects susceptibility to weathering (Limestone vs Quartz as examples).
  • Rock structure: joints, folds, faults increase weathering rate by enabling agent access.
  • Topography: steeper slopes expose rocks to more weathering agents.
  • Time: longer exposure increases weathering.

EXOGENIC PROCESSES (WEATHERING VS EROSION)

Exogenic processes include weathering plus erosion and deposition.

EROSION AND DEPOSITION

  • Erosion is the transport of material by a mobile agent (water, wind, ice).
  • Deposition is the accumulation of transported sediments.

AGENTS OF EROSION

  • Running water
  • Sea waves
  • Glaciers
  • Wind
  • Gravity

RUNNING WATER

  • Overland flow: sheet flow downslope.
  • Streamflow: water in a defined channel.

STREAM EROSION FACTORS

  • Velocity
  • Discharge (throughput of water)
  • Channel shape and roughness

LANDFORMS OF RUNNING WATER

  • Erosional features: river valleys, waterfalls, potholes, terraces, gulleys/rills, oxbow lakes, peneplain.
  • Depositional features: alluvial fans, natural levees, deltas.

OCEAN OR SEA WAVES

  • Erosional features: wave-cut cliff, wave-cut platform, marine terrace, headland, sea arch, sea stack, sea cave.
  • Depositional features: beaches, spits, baymouth bars, tombolos, barrier islands, lagoons.

GLACIERS

  • Types: valley (alpine) glaciers, ice sheets (continental), ice shelves.
  • Erosion: glacial plucking and abrasion.
  • Plucking: meltwater infiltrates bedrock, freezes, and removes chunks.

WIND

  • Erosion by wind: deflation (removal of loose fine particles) and abrasion (sand-blasting); wind generally shapes landscapes with limited erosion compared to water.
  • Dunes and loess are common wind-formed features.

GRAVITY AND MASS WASTING

  • Mass wasting is downslope movement driven by gravity.
  • Common types: solifluction, earthflow, soil creep, slump, debris slide, mudflow, debris flow, rockfall.

CONTROLLING FACTORS IN MASS WASTING

  • Shear strength vs shear stress: movement occurs when shear stress exceeds shear strength.
  • Slope angle: steeper slopes have greater downslope force.
  • Water: adds weight and reduces shear strength; affects angle of repose.
  • Material properties: rock weakness and texture influence stability.
  • Time: longer exposure increases risk of failure.

ENDURING UNDERSTANDING

Weathering breaks rocks into mineral components and also creates new compounds; these processes can concentrate valuable mineral ores (e.g., iron, manganese, tin, aluminium, uranium).

GENERALIZATION

Physical weathering disintegrates rocks; chemical weathering decomposes rocks by chemical reactions that alter minerals.

REVIEW (SUMMARY DEFINITIONS)

  • WEATHERING: disintegration/decomposition of rocks near the surface.
  • PHYSICAL WEATHERING: mechanical breakdown into smaller pieces.
  • CHEMICAL WEATHERING: chemical alteration of minerals.
  • EXFOLIATION: removal of outer rock layers due to heating.
  • FROST WEDGING: freeze-thaw pries rocks apart.
  • BLOCK DISINTEGRATION: heating/cooling expansion/contraction.
  • SALT CRYSTAL GROWTH: pressure from salt crystals in pores.
  • ABRASION: wearing away by particle collision.
  • HYDROLYSIS: minerals react with water to form new minerals.
  • DISSOLUTION: minerals dissolve in water/acid.
  • CARBONATION: carbonic acid formation from CO₂ and water.
  • OXIDATION: oxidation of minerals (e.g., Fe to Fe oxide).
  • MASS WASTING: gravity-driven downslope movement of soil/rock.
  • AGENTS OF EROSION: running water, wind, waves, glaciers, gravity.
  • LANDFORMS: erosional (valleys, cliffs, arches) and depositional (deltas, beaches, spits).