Weathering_and_Erosion

Weathering and Erosion

Overview

• Weathering and erosion are interconnected processes that shape the Earth's surface and affect the rock cycle.

Weathering in the Rock Cycle

• Key components of the rock cycle include:

  • Igneous Rocks: Formed from cooled magma.

    • Magma: The molten rock below the Earth's surface.

    • When magma cools, it forms igneous rocks.

  • Sedimentary Rocks: Created from sediments deposited over time, often compacted or cemented together.

  • Metamorphic Rocks: Formed under heat and pressure.

    • Cementation: The process where minerals fill the spaces between grains to bind them together.

Three Main Processes of Weathering and Erosion

• Weathering: Disintegration or decomposition of rock at or near the surface.

  • Two types:

    • Mechanical Weathering: Physical breakdown of rocks.

    • Chemical Weathering: Chemical breakdown of minerals.

• Erosion: The process by which weathered material is removed from one location and transported to another.

• Mass Wasting: Movement of soil and rock down a slope due to gravity.

Types of Mechanical Weathering

• Frost Wedging:

  • Water penetrates cracks in rocks, freezes, expands, and eventually forces the rock apart.

• Salt Wedging:

  • Minerals grow in the cracks of rock, exerting pressure on the surrounding material.

• Biological Weathering:

  • Roots of plants penetrate cracks and physically break apart rocks as they grow.

• Unloading/Exfoliation:

  • Reduction of pressure on rocks (like when overlying materials are removed) causing them to expand and crack.

• Thermal Expansion:

  • Repeated heating and cooling of rocks lead to expansion and contraction, causing cracks.

Chemical Weathering

• Involves the chemical alteration of minerals.

• Results in new ions in solution which can lead to the salinity of bodies of water like oceans.

Types of Chemical Weathering

• Hydrolysis: Water reacts with minerals to form clay:

  • Example: KAlSi3O8 + H2O results in clay and dissolved potassium & bicarbonate ions.

• Dissolution: Minerals dissolve, typically salts and carbonates, leaving ions in solution.

• Oxidation: Minerals (often containing iron) lose electrons resulting in oxidation (e.g., rusting of iron).

Results of Weathering

• Production of regolith: Loose broken rock and mineral fragments.

• Release of dissolved ions into solution, contributing to soil formation and nutrient availability.

• Creation of soil and various sizes of sediments, including clay, sand, and gravel.

Erosion and Transport

• Erosion: Transport of unconsolidated material from one location to another.

  • Agents include water, wind, ice, and gravity.

  • Erosion leads to the movement of materials such as sands and gravels from one place to another.

Erosion by Water

• Flowing Water: Acts as a powerful agent by moving and redistributing sediments.

• Saltation: Movement of particles in short jumps.

• Bed Load: Materials transported along the bottom of streams.

• Suspended Load: Material carried within the water column.

Erosion by Wind

• Deflation: Removal of small, loose materials by wind, leading to lowered surface levels.

• Abrasion: Wind-driven particles abrade surfaces, altering landscapes.

Erosion by Glaciers

• Glaciers entrain rocks and sediments, which are deposited unsorted as the glacier melts.

• Glacier dynamics include calving (breaking off) when they enter bodies of water, contributing to erosion and material transport.

Erosion by Gravity

• Gravity results in the downward movement of materials, contributing to mass wasting events such as landslides.