GLG 101

Chapter 9

Mass Wasting

Mass wasting: downward movement of material due to gravity

What influences mass wasting?

- shear strength of the slope:

-material strength and cohesion of slope

-amount of internal friction between grains

-external support of the slope

angle of repose: steepest angle a slope can maintain without collapsing

- slope gradient: the steeper the slope, the less stable it is

-undercutting by stream or wave action

-road cuts, building sites

-weathering and climate: humid climates result in deeply weathered rock

-water content: influences slope stability, weight of water, percolating water reduces friction

-vegetation: absorption of water, roots stabilize slope

-overloading: by human activity, dumping, filling, piling up of material

-geology and slope stability: dip-slope surfaces more likely to fail

Triggering mechanisms:

most common: earthquakes and excessive amounts of water

Types of mass wasting:

falls: rock falls through air from steep cliff (fast movement)

slides: movement along curved surface of rupture

-slump: (very slow movement)

-rock glide (rapid)

flows: rock plus water

-mudflow: 30% water (very rapid)

-debris flow: <30% water (rapid to very rapid)

-earthflow: thick, viscous flow of soil (slow to moderate)

-quick clays: fine material, flows like water (rapid to very rapid)

-solifluction: water-saturated surface sediment (slow)

-creep: movement of soil and rock (slow)

complex movements: slow to very fast