Week 7: Mass Wasting Flashcards
What is Mass Wasting?
The downhill movement of masses of soil, rock, mud of other unconsolidated materials under the influence of gravity. Movement occurs when gravity exceeds strength of slope materials.
e.g.: rock avalanches, debris flows, mudflows, creep
What are common triggering mechanisms for mass wasting?
- earthquakes
- floods
- freeze-thaw action
What are the three principle factors that influence mass movements?
- nature of the slope material (solid rock, sediment, soil)
- amount of water in materials
- steepness and instability of slope
What are unconsolidated materials?
Any loose and uncemented material
What is the angle of repose and what is its importance?
The maximum angle at which a slope of loose material will lie without cascading down. Important for stability of unconsolidated materials.
What are consolidated materials?
This includes rocks and vegetated soils. Slopes of the materials can be steeper and more irregular than unconsolidated.
What does failure of consolidated materials require?
Overcoming cohesion and shear strength of the material
How does water content affect the stability of unconsolidated materials?
A thin film of water increases surface tension and thereby increases angle of slope at which it can remain stable. However exceesive amounts of wtaer will saturate the material and greatly reduce the strength.
e.g. moist sand best for sand castles
What are common triggers for Mass Wasting, and which one is most important?
- heavy rainstorms
- vibrations from earthquakes <– Most important
- freeze-thaw action
- volcanic activity
- gradual steepening
What is Liquefaction?
The process whereby a water-saturated material liquefies into a fluid slurry
What are the 3 characteristics of mass movement?
- the nature of the material (rock or sediment)
- the speed of movement
- the nature of the movement. Whether it is sliding in which the bulk of the mass moves as a unit, or flowing in which the material behaves as if it were a fluid.
What are 3 types of Rock mass movement?
- rockfalls
- rockslides
- rock avalanches
What are Rock Falls?
Individual blocks that detach from a slope and plummet in freefall from a cliff or steep mountain slope
What is Talus?
Accumulation of rocks at the foot of a steep cliff
What are Rock Slides?
They occur when rocks slide rapidly down a slope rather than free falling
