Erosion and Weathering Processes

Gravity and Erosion

  • Gravity is identified as the primary driver of erosion in high-top areas.

  • Sediment accumulates in basins, typically formed by various geological activities.

  • Sources of sediment mainly include mountain ranges.

Basin Formation

  • A basin is formed through a process called subsidence which involves:

    • The lowering of the earth's crust to create a depression that collects sediment.

  • Various factors affecting the type and maturity of basins also influence permeability and porosity of sediments.

Weathering Processes

Weathering Overview

  • The process of weathering can be summarized in three steps:

    1. Weathering

    2. Transport

    3. Deposition

Types of Weathering

Physical Weathering

  • Defined as the physical disintegration of older rocks into smaller particles without chemical change.

  • Example: Freeze-thaw cycles of water can lead to the expansion of ice, resulting in angular blocks of rock as volume increases.

  • Insolation weathering occurs due to:

    • Exterior heating causing greater expansion than the interior, leading to:

    • Stress from thermal expansion and contraction, resulting in rock fracture.

Salt Weathering

  • Involves the crystallization of salts within pore spaces, exerting pressure on surrounding materials.

Wet/Dry Cycles

  • The alternating cycles of wetting and drying, particularly in softer rocks, promotes rapid breakdown due to:

    • Physical stress release which can occur when burial rocks experience high compressional stress followed by expansion when weight is removed.

    • This can lead to the creation of parallel fractures known as sheeting.

Additional Types of Physical Weathering

  • Spheroidal weathering: A smaller scale of sheeting around rock outcrops.

  • Hydration of clays (e.g., expansion of clays upon absorbing water) leading to physical disintegration, known as exfoliation.

Chemical Weathering

Hydrolysis

  • Occurs when acidic water reacts with minerals such as clay, resulting in new material formation.

Simple Solution

  • The dissolution of minerals in acidic water, leading to complete solubility.

Oxidation

  • Involves the loss or sharing of electrons with oxygen, affecting compounds like iron.

Reduction

  • The gain of electrons by iron, transforming it into different oxidation states.

Ion Exchange

  • Process leading to clay formation, e.g., the transition from Hematite to Goethite through the addition of water:

    • \text{Hematite} + \text{H}_2\text{O} \rightarrow \text{Goethite}

Hydration and Dehydration

  • Hydration: Adding water to minerals.

  • Dehydration: Loss of water leading to anhydrous states.

Chelation

  • Refers to the bonding of metal ions with organic substances such as those from lichens, impacting mineral availability.

Biological Weathering

  • Biological weathering comprises processes where living organisms contribute to the breakdown of rocks:

    • Burrowing activities move rocks and soil to the surface.

    • Plant roots penetrate and break apart soil and rock structures.

    • Microbial activity alters rocks chemically via:

    • Symbiotic relationships, e.g., lichens, where fungi release chemicals that assist in breaking down minerals while algae assimilate nutrients gained from this process.