Chapter 11 -- Mass Wasting Flashcards
(34 cards)
Mass Wasting includes these 7 things…
Landslides, Earthflows, Mudflows, Rockfalls, Debris and Snow Avalanches, and Subsidence.
is the downslope of movement of material resulting from the force of gravity.
Mass Wasting
Slopes shear strength
Depends on forces called ______ ______ that oppose downward movement and help maintain slope stability.
Material’s strength and cohesion
Internal friction between grains.
External support of the slope.
Resisting Forces
Is a driving force which opposes a slope’s shear strength and moves material down slope.
Gravity
Driving Forces Include 3 things…
Weight of slope material
Vegetation
Structures on the Slope
Probably the major cause of slope failure.
The steeper the slope, the less stable it is.
Slope Angle
Maximum angle at which unconsolidated material on slope is stable. ~##-##°
Controlled by coarseness, shape, size and uniformity of size of fragments water content, etc..
Angle of Repose
30-35°
Mass wasting is more likely to occur in highly weathered slope material than in bedrock.
Weathering
Characteristic weather at a specific place over time. This includes, the average temperature and precipitation which affects vegetation and therefore affects slope stability.
Climate
Almost always involved with mass movements.
_____ fills pore spaces between sediments, reduces internal resistance, and adds weight.
Effects: Decreasing stability when slope becomes saturated. Slumps or slides can occur years after deep water infiltration. Can erode base or toe of slope decreasing it’s stability.
Water
Stream or wave _______ may remove material creating steeper slope thus reducing safety factor. This may reactivate old landslides.
Erosion
Pros and Cons of Vegetation \+ \+ \+ -
+ Shields soil thus mitigates runoff.
+ Helps absorb water from the rains
+ Roots help fix soil in place.
- Adds weight to the slope.
Almost always from human activity such as dumping, filling, or piling up of material
Can increase water pressure within the slope material.
Decreases shear strength and thus weakens the slope material.
Overloading
Triggers of Mass Wasting (6)
Earthquakes Heavy precipitation Volcanic Eruptions Thunder ----If the slope is sufficiently unstable. Gunshot or Loud Shout Some Avalanches
_____ _______ depends on the driving and resisting forces that act on the slope.
Slope Stability
Types of Mass Wasting
Extremely Rapid
Rocks of any size free fall through the air.
Falls
Types of Mass Wasting
Variable rate
Downslope movement of material along one or more surface of failure.
Slide
Types of Mass Wasting
Slow to moderate
Occurs along a curved surface of rupture
Slump
Types of Mass Wasting
Rapid
Occurs along planar surface.
Rockslide
Types of Mass Wasting
Rapid downslope movement of snow and ice sometimes with rock, soil, and trees.
Can travel as much as 62 mph.
Tend to travel down chutes where previous _________ have flown.
Avalanches
Downslope movement of unconsolidated Earth material saturated with water.
Main types are:
Flows
Mud Flows, Debris Flows, Earth Flows
> 50% of particles are finer than sand
Up to 30% water
Common in arid and semiarid climates after severe storms.
Mudflows
> 50% of particles are coarser than sand.
Contains less water and larger particles than mudflows
More viscous than mudflows and move more slowly.
Debris Flows
Move downslope as thick, viscous masses of wet regolith
Move more slowly than debris flows or mudflows
Earth Flows
