Soils and Erosion

Factors Controlling the Rate of Chemical Weathering:

• particle size (edges and corners), climate (water and temperature), parent material
  • the smaller the particles, the higher the ratio of surface area to volume
  • hot humid climates increase speed and depth of weathering
  • inverse of Bowen's reaction series (see Igneous Rock chapter)
  • igneous minerals are out of equil. at surface
  • spheroidal weathering

Soil:

• regolith is the general term for broken up rock material
• regolith + water + air + organic matter = soil
• humus: partly decayed organic material
• residual vs transported soils

Soil layering or profile: O, A, B, C

• leaching vs. accumulation

Factors controlling soil formation:

• climate
  • pedalfers: Al and Fe-rich, water flow downward, >60 cm/yr precip.
  • pedocals: Ca or calcite-rich, water flow upward, <60 cm/yr precip.
    • extreme example: caliche soil in desert setting
  • laterites: extreme leaching of everything except Fe or Al (bauxite), tropical
• parent material: e.g. quartzite vs granite
• organic activity: animals, organic acids
• relief and slope: steep vs shallow, high vs low elevations, facing direction
• time: average of 2 cm/century - non-renewable resource

Soil Degredation:

• erosion: wind or water; sheet erosion, rill erosion [SLIDES]
• chemical deterioration
  • nutrient depletion
  • insufficient fertilizer
  • clearing land: low quality soils in rainforests
  • pollution
• salinization
• physical deterioration: compaction

Desertification: positive feedback process

• erosion in the Sahara actually feeds the Amazon rainforest
• soil erosion can poison coral reefs (the ocean equivalent to the rainforest)

Weathering and Mineral Resources:

• bauxite, iron, manganese, clays, tin, gold, diamonds
• direct shipping ores (iron, Ladysmith Cu)
• supergene enrichment­ gossans