Topics for today Mass Wasting (Ch ) 1. Controlling factors –Soil strength –Hill slope gradient 2 Physical model 3 Natural cases –Rain storms –Timber harvesting –Roads 3. Coefficient of friction Water in soils 4.Mechanisms of movement 5.Mass wasting types 6.Large landslides
Mass wasting
Mass wasting is the down slope movement of rock, regolith, and soil, under the influence of gravity.
Rock fall
Landslide
Creep
Debris flow
Coefficient of friction
Angle of repose = angle of internal friction in dry, loose material
Cohesion
Water reduces cohesion, removes frictional contact between grains
Landslide
Mechanisms of movement Pure flow –Earth flows –Mudflows Pure slide/fall –Rock falls –Avalanches –landslides Creep –Gradual movement - Freezing cycles
Dry mass wasting from Slow to fast Creep >Rock fall
Creep
Soil Creep
Creep
Rock fall
Talus slope
Slow-medium velocity mass wasting from dry to wet
Earthflow
6 m/yr Highway 149 The earthflow began 700 years ago. About 350 years ago, a second earthflow Slumgullion Earthflow, CO
Solifluction
Fasts mass wasting processes from dry to wet
Rockfall
Debris avalanche
Mud flow
Blackhawk rockslide, Ca
It is a prehistoric landslide ~20,000 years old Source was 4000 ft height 5 miles long X 2 miles wide X 50 feet thick Velocity = 270 miles/hour Traveled time 8 sec
Huascaran Debris avalanche, Peru (1970)
Huascaran (6768m) Trigger by an earthquake M=8 Buried the city of Yungay, 18,000 people died Traveled 9 miles mph
Explanations Liquefaction-wet Air cushioning Acoustic fluidization (high vibration)
Liquefaction Lost of friction between grain
Air cushioning Air layer underneath the slide reduces friction and can travel farther.
Acoustic fluidization (high vibration)