Understanding Soil Formation, Classification, and Erosion Impacts

Posted on Mar 9, 2025 in Geology

Factors Leading to Soil Formation

  • Weather: Water balance, increased temperature.
  • Topography: Favors erosion, hindering soil formation.
  • Nature of the Bedrock: Soil components depend on the minerals present.
  • Biological Activity: Decaying matter contributes to organic matter formation.
  • Time: Soil regeneration is slow, making it a non-renewable resource.

Soil Classification

Zonal Soils

Zonal soils, found in areas like polar regions and deserts, lack distinct horizons.

Azonal Soil Types

  • Soils of Humid and Cold Climates (Podsols): Occur in cold and temperate regions with heavy rainfall. Acidic due to slow humus decomposition. Typical of coniferous forests.
  • Soils of Temperate Zones: Result from seasonal changes in deciduous or sclerophyllous forests. Accumulate significant humus that decomposes slowly due to climate.
  • Soils of Arid Climates: Low rainfall leads to constant capillary rise, forming surface crusts of gypsum or salt.
  • Soils in the Tropics: High temperatures and rainfall promote bacterial activity, causing rapid organic matter decomposition. Results in a thin A horizon with little organic matter.

Azonal Soils

These soils are in early stages of ecological maturity. Ranker soils form over silica-rich rock, while rendzinas form over limestone. Gley soils develop in cold, wet environments.

The Impacts of Soil Erosion

Erosion is a natural process intensified by human activities, causing ecological and societal consequences.

Implications of Soil Erosion

  • Grounding
  • Worsening floods
  • Deterioration of ecosystems
  • Formation of sand and gravel pits
  • Loss of arable land and fertility

Factors Influencing Erosion

  • Climate type
  • Relief
  • Soil type and vegetation
  • Human land use

Erosivity

Erosivity expresses the erosive capacity of weather-dependent geological agents. It’s crucial for developing national erosivity maps and can be evaluated by:

  • Aridity index
  • Climatic aggressiveness rate
  • Rainfall erosion index

Erodibility

Erodibility is the substrate’s susceptibility to erosion, depending on soil type, slope, and vegetation cover. It’s useful for creating local erodibility maps.

Values of Erosion

  • Slopes
  • State of plant cover
  • Land susceptibility

Methods of Erosion Evaluation

Direct Methods

Applicable in specific areas, providing accurate data on erosion speed and magnitude.

Physical Indicators

Assess erosion based on observable marks in the field:

  • Grade 1
  • Grade 2: Sheet erosion, erosion in furrows
  • Grade 3: Gully erosion

Biological Indicators

Vegetation serves as a bioindicator of soil conditions:

  • Null Level
  • Low Grade
  • Medium Grade
  • High Grade

Indirect Methods

The Universal Soil Loss Equation (A = RKLSC P) is frequently used, where:

  • A: Average annual soil loss
  • R: Rainfall erosivity factor
  • K: Soil erodibility factor
  • L: Slope length factor
  • S: Slope steepness factor
  • C: Cropping management factor
  • P: Erosion control factor