Geography 323 -- Geomorphology


Functions of weathering

  1. gives rock lower strength and greater permeability, rendering it more susceptible to mass wasting and erosion; reduces strength (cohesion and friction) and increases permeability of rock and therefore decreases resistance to fluid and gravitational stresses; precursor to erosion
  2. produces minor landforms, produces landforms in soluble rock (especially limestone) and otherwise creates microrelief (e.g. weathering pits)
  3. releases minerals in solution (e.g. iron oxides, silica, carbonates) which become concentrated to form hard coatings on rocks and hard resistant layers in soil (duricrusts) that inhibit seepage and resist erosion
  4. first step in soil formation; ultimately produces an unconsolidated mass of 1) minerals that resisted alteration (e.g. feldspar), 2) new minerals (e.g. bauxite), 3) organic debris

Physical weathering


  1. stress (pressure) release: disintegration of rock in parallel sheets as it expands in response to the removal of confining stress
  2. thermal expansion and contraction (insolation weathering)
  3. growth of foreign crystals (salt weathering)
  4. hydration (slaking)

    Expansion of Clay Minerals by Volume
    Na-montmorillonite (bentonite)1400-1600%

  5. frost shattering and hydration shattering
  6. plants

Chemical Weathering


  1. oxidation
  2. hydroloysis
  3. carbonation (solution)
  4. cation exchange
  5. chelation

Climate and weathering

[ Course Outline | Next Topic ]