Mass Movements Flashcards
What is the common characteristic of all mass movements?
The downward movement of material on a slope.
Name two examples of unconsolidated mass movements.
- Rockfalls
- Avalanches
What are the two types of mass movements based on material consistency?
- Unconsolidated material
- Consolidated mass
What forces influence slope stability?
- Gravity
- Shear strength
- Shear stress
Shear stress is resistive force developed per unit area in a body due to the applied Shear force. Shear force causes shape changes without changing the volume of the body.
Strength is the ability of a material to resist external load against failure. Strength is property and fixed for a particular material.
Define shear strength in the context of slope stability.
The forces that maintain a slope’s stability and prevent movement.
Define shear stress.
The forces acting to reduce slope stability and lead to movement.
What happens when shear stress is greater than shear strength?
There will most likely be a mass movement.
List the most important factors influencing slope stability.
- Gravity
- Slope angle
- Pore water pressure
What does pore water pressure refer to?
The weight of water within the soil or rock and its attempt to move downslope.
How does water affect slope stability?
Acts as a lubricant causing greater instability.
What human activities can undermine slope stability?
- Deforestation
- House construction
- Road construction
What are the two functions of trees in relation to slope stability?
- Bind the soil increasing shear strength
- Reduce pore water pressure
What can be a consequence of building houses on a slope?
Increases shear stress due to added weight.
What causes mass movements to occur?
An imbalance between shear strength and shear stress.
Name two slow-moving mass movements.
- Soil creep
- Scree creep
What is solifluction?
A consolidated flow of material occurring in regions of permafrost.
What is the effect of soil creep over time?
Destabilizes walls, fence posts, and electrical lines.
How can mass movements be classified?
Based on speed of flow and degree of fluidity.
What are the four forms of fast-moving mass movements?
- Falls
- Topples
- Slides
- Flows
What is a rotational slump?
A mass movement where a slump block slides along a concave slip plane.
What are debris flows?
Water-laden masses of soil and fragmented rock that rush down mountainsides.
What is the typical speed of debris flows in steep channels?
Surpass 10 meters per second.
How does the frequency of mass movements correlate with their magnitude?
Small-scale movements occur more frequently than large-scale movements.
