March 14th Geo lecture
Chapter 1: Introduction to Mass Movements
Overview of Slopes and Mass Movement
Increased risk for mass movements on slopes
The angle of the slope can increase due to erosion at the bottom.
Erosion makes slopes steeper, which is critical for understanding mass movement risks.
Role of Vegetation
Vegetation impacts slope stability: can stabilize or destabilize.
Positive Effects:
Protective cover: Vegetation intercepts rainwater, reducing soil saturation.
Root systems draw water from the soil, minimizing saturation and stabilizing slopes.
Roots act like reinforced concrete, anchoring sediments in place.
Negative Effects:
Heavy vegetation adds weight, increasing driving forces that contribute to mass movements.
Roots in rocky areas can create fractures that destabilize the slope.
Studies suggest the overall effect of vegetation on slopes is positive, increasing stability.
Impact of Deforestation and Forest Fires:
Removal of vegetation exposes soil to water, making slopes less stable.
Water and Slope Stability
Water can act as an undercutting agent:
Wave action or river erosion at the base of a slope decreases stability.
Reduces support for the upper slope when material is removed.
Water weight increases the mass of the slope, helping destabilize it.
Saturation of Soil:
Saturation leads to decreased cohesion and friction, making slopes more prone to failure.
Saturated soil can result in debris flows, where water mixes with sediments to create a flowing mass.
Liquefaction occurs when soil loses cohesion due to saturation, potentially leading to significant mass movement.
Chapter 2: Single Mass Movements
Effects of Water on Mass Movements
Water contributes to erosion and acts as a weight increasing the driving force on slopes.
Major examples include areas prone to coastal erosion and glacial tilts.
Notable Case Studies:
East Sussex Coast:
Erosion by waves illustrated by the chalk cliffs undergoing undercutting.
Inland Erosion:
Glacial tilts showing faster coastal erosion rates.
Chapter 3: The Active Layer
Permafrost and Ground Saturation
Permafrost represents ground permanently frozen, impacting water cycle and stability.
Thawing creates an active layer that can easily become saturated and lead to instability.
Ground Conditions Contributing to Mass Movement
Saturation of the active layer is crucial for understanding the dynamics of mass movement.
Chapter 4: Specific Mass Movement Factors
Types of Mass Movements
Triggers vs. Conditions: Recognizing triggers (like earthquakes) as the immediate cause of mass movement which can be influenced by long-term conditions of slope instability.
Importance of Water: Both as a destabilizing force and a trigger for potential mass movement events.
Chapter 5: Types of Movement
Free Fall, Sliding, and Flow
Classifications based on movement type and material involved.
Free Falls: Rapid descent of rocks without contact with ground.
Slides: Material moves along a failure surface while remaining fairly coherent.
Flows: Mixture with water or air leading to mass movement events.
Chapter 6: Case Studies of Movement
Rock Slide Examples:
The 1996 Yosemite rock fall case demonstrating dynamics of free fall and impacts.
The Frank’s Slide (1903) where large-scale movement resulted in significant fatalities and discussions on geological factors.
Chapter 7: Impacts of Slope Stability Factors
Conditions Leading to Instability:
Evaluated key geological conditions like type of material, slope angles, climate influences, and water presence contributing to mass movements.
Analysis includes the critical role played by weather patterns in heightening vulnerability.
Chapter 8: Conclusions
Key Takeaways:
Gravity is the main driving force behind mass movements, with a complex interplay of water, material type, vegetation, and slope topography contributing to slope failure.
Importance of understanding these interconnected factors for geological and environmental sciences.