Weathering and Mass Wasting Lecture Notes

Introduction

• Focus: Weathering and mass wasting
• Context: Earth's processes; building up (geological activity) vs. breaking down (weathering & erosion)
• Main Themes: Erosion, transportation, deposition

Basic Processes

• Weathering: Initial breaking down of Earth's materials
  • Types: Physical and chemical
• Transportation: Movement of weathered material
  • Mass Wasting: Movement of large amounts (e.g., landslides, avalanches)
• Deposition: Settling of transported material

Weathering

• Physical Weathering: Breaking down of material by physical forces
  • Examples: Ice wedging, wind abrasion, ocean waves
• Chemical Weathering: Introduction of new chemicals that alter material
  • Examples: Acid rain, oxidation
• Result: Formation of regolith (weathered rock particles above solid rock)

Regolith

• Definition: Surface layer of weathered rock particles above bedrock
• Composition: No biomass, just broken-down rock

Mass Wasting

• Definition: Movement of large amounts of Earth material
• Examples: Landslides, avalanches, debris flows

Case Studies

• La Conchita Landslides: Vulnerable due to steep, dry slopes
• Montecito Debris Flow: Result of fire removing stabilizing vegetation, followed by heavy rain

Factors Affecting Weathering

1. Type of Rock: Vulnerability depends on rock type (e.g., sandstone vs. granite)
2. Exposure: More sides exposed leads to faster weathering
3. Climate: Extreme temperature changes increase vulnerability (e.g., desert conditions)
4. Fractures and Joints: Natural lines of weakness in rocks
5. Porosity: More porous rocks weather faster
6. Biological Factors: Plants and animals can both mechanically and chemically weather rocks

Types of Physical Weathering

• Frost Action: Water freezes in cracks, expands, and breaks rock apart
• Salt Crystal Growth: Salt expands when warmed, breaking rock
• Exfoliation: Removal of surface layers due to temperature changes or heavy weights moving
• Thermal Action: Expansion and contraction due to temperature changes
• Biological Action: Roots and burrowing animals breaking rock apart

Chemical Weathering

• Hydrolysis: Water introduces new chemicals
• Oxidation: Reaction of oxygen and water, often with metals like iron
• Carbonation: Acidified water dissolves rocks like limestone
• Chemical Precipitation: Formation of new solids from liquid chemicals

Special Focus: Karst Landscapes

• Formation: Rainwater with carbon dioxide dissolves limestone, creating caverns
• Importance: Significant geological features formed by chemical weathering

Summary

• Weathering: Breakdown of Earth materials by physical and chemical processes
• Mass Wasting: Large-scale movement and deposition of weathered material
• Focus: Understanding these processes is crucial for studying Earth's surface changes

Next Steps

• Detailed discussion on mass wasting processes and more case studies