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)