Transcript mass_wasting

This is the downward movement of material under the
influence of gravity
Water can play an important role, but gravity is the main
element
All slopes are in a state of dynamic equilibrium between
gravitational forces and resisting forces.
Factors that resist gravity include
the materials strength and cohesion
vegetation
internal friction between grains
Angle of underlying rock
Factors that help gravitational forces
increasing the slope angle
under cutting of the slope
amount of weathering
amount of water moving through material
overloading slopes with new material
Erosion by a river
increases slope angle
Excavation at the base of a slope can lead to slope instability
i.e. road cut along slopes
Slope failure caused by over loading
The angle at which the underlying rock is inclined has a major
impact on mass wasting.
Mass wasting is often caused by a force that
temporarily disturbs the slope equilibrium
•Earthquakes
•Heavy rain
•Leakage from water pipes and swimming pools
•Volcanic eruptions
• explosions
• thunder
Falls
•Rockfalls
Slides
•Slump
•Rockslide
Flows
•Mudflow
•Debris flow
•Creep
•Solidification
Complex movements
A Rockfall is any rapid mass movement in which rocks fall
through the air.
Which rocks are more likely to have rockfalls?
Fractured,
steep slope
Slides:
These are slow to rapid movement of material along one or
more surfaces.
Slumps are
Usually slow to moderate in speed
Movement along a curved surface
Usually in unconsolidated materials like soil
Rockslides are
rapid to very rapid
movement along a planar surface
A Slump
Slump caused by erosion in southern California
Rock slides
Flows:
These are mass movements where the material moves as a
viscous fluid or plastic movement
Mudflows are very rapid and contain a lot of water and mud
Earthflows are slow to moderate movement of material
down a slope which leaves an exposed scrape.
Solidification is the slow downward movement of water
saturated soil. Common in areas of permafrost
Creep is extremely slow movement of soil & rock downhill
An Earth flow:
Solidifluction: in Alaska
Creep
Solutions to Mass wasting:
Surface and subsurface drainage of hillsides
Replanting of vegetation
Reduce the angle of slope
Putting in retaining walls and bolting rock faces