Earth’s Surface Processes: Weathering, Soil, Erosion, Transport

Posted on May 15, 2025 in Geology

Geological Processes

Transformation of rock by the action of weather and living organisms.

Transformations that alter the physical structure of rock (e.g., temperature contrasts) without changing its chemical composition.

Chemical reactions within the rock that transform minerals into new substances (e.g., due to rain, humidity).

Solution: Dissolving of certain rocks, creating sinkholes or cavities.
Carbonation: Dissolving rocks through reaction with carbon dioxide.
Hydration: Minerals absorbing water and swelling (e.g., expansive clays).
Oxidation: Reaction of minerals (especially iron) with oxygen (e.g., rust).
Biological Weathering: Chemical reactions on rocks caused by living organisms.

The interface consists of four subsystems: atmosphere, hydrosphere, lithosphere, and biosphere.

Soil: The surface layer of the Earth’s crust formed by the alteration of bedrock due to external geological agents and weather.

Loss of soil by water or wind.

Loss of soil fertility.

Chemical Deterioration: Caused by chemical processes, often related to soil contamination (e.g., industrial discharges, mining) or excess irrigation (leading to increased salinization, denitrification).
Physical Deterioration: Soil compaction (e.g., heavy machinery, overgrazing).
Biological Deterioration: Loss of humus or lack of organic matter decomposition.

Slope: Erosion increases with the steepness of the slope, as materials become more unstable. A flat surface erodes less easily than an inclined one, even if the inclination is low. Over time, slopes naturally soften, reducing erosion. Artificial slopes (like road cuts) and cleared land with steep slopes experience more intense erosion.
Weight of Materials: Increased mass on a slope increases gravitational force, making the slope more unstable and susceptible to erosion (e.g., building on a cliff top, depositing debris).
Lack of Cohesion: Internal cohesion is the bond between particles in a rock. Increased cohesion increases resistance to erosion. A rock is more likely to slide downhill if:
- It has cracks.
- It is soft, weathered, or unconsolidated.
- Even hard rock slides better if soaked in water or has a smooth surface.
Absence of Vegetation: Vegetation protects against erosion by holding soil with roots, preventing slipping.

Sediment transport is the transfer of eroded materials to the place where sedimentation occurs, carried out by external geological agents.

Selective Transport: Materials are selected according to size. Heavier materials are deposited first as the transport agent’s energy decreases. Lighter particles are carried farther. River water and wind are examples of agents performing selective transport.