Mass Wasting Sculpturing Earth’s Landscape. What is Mass Wasting? The downslope movement of material under the influence of gravity May occur at rates.

Mass WastingMass WastingSculpturing Earth’s Landscape

What is Mass Wasting?What is Mass Wasting?

• The downslope movement of material under the influence of gravity

• May occur at rates of only a few inches per year– result in little damage and no loss of life

• May occur at over 100 mph– result in great loss of life and property damage

Mass Wasting – Factors Controlling Mass Wasting

• Angle of Repose

• Pore Water

• Material

• Orientation of Rock Layers

• Vegetation

Mass Wasting - Factors

• Angle of Repose

–Major determining factor in slope stability– Every material and

slope has an inherent angle it becomes unstable.

– The angle at which loose material sits at rest

– Typically 25°-40°

Angle of repose

• In general, coarser grained, poorly sorted, and angular rocks have a higher angle of repose

Mass Wasting - Factors

• Pore Water

– Adds weight

– Provides lubrication

–Water held within the void spaces

–May provide surface tension

When Saturated:

Pore Water

• No water – grains held together by frictional forces

• Some water– Grains held together by surface tension

• Too much water– Provides lubrication and grains move freely

Mass Wasting – Factors

• Material

– Loose soil and sediment are more prone to slope failure

– Sand material have greater pore spaces

– Horizontal layers are more stable than loose sediment

–Massive rocks tend to be the most stable

Mass Wasting – Factors

• Orientation

– pertains to layered rocks

–When layers dip in the same direction as slope, failure is more likely

– Horizontal layers are more stable

–Most stable is when rock layers dip into slope

Mass Wasting - Factors

• Vegetation

– roots form an anchor for soil– reduces amount of water in pore spaces

Mass Wasting - Factors

Mass Wasting - Types

• Slow Movement

– Creep

• Rapid Movement– Rock fall

– Slump

– Rock slide

– Debris Flow

Mass Wasting – Types (slow)

• Creep– Gradual downhill

movement of slope material

– Result in tree trunks to curve at base

Mass Wasting – Types (fast)

• Rock fall

– Free fall of detached pieces of material of any size

–May occur as a result of freeze-thaw

–May occur by the loosening action of plant roots

Mass Wasting – Types

• Slumps

– A mass of material sliding along a curved, rotational surface (shaped like a spoon)– Scarp is crescent-shaped

cliff at upslope end

– Bulge is usually at toe where soil accumulates

Mass Wasting – TypesMass Wasting – Types

• Rockslides

– Also called “landslides”

– Blocks of rocks and soil move down a well-defined plane (sliding)– Among the most

destructive

– May be triggered by rain, melting of snow, or earthquakes

Mass Wasting – Types

• Debris Flows

– Commonly occur in volcanic areas

– Downslope movement of a viscous (thick) fluid

– Typically follow drainage patterns (valleys)

Mass Wasting – Classification Types

Mass Wasting Potential

Road Cut Brush Fires

Volcanoes

Heavy Rains

Debris Flows

Nevado del Ruiz

Monterey Hills

Mass Wasting Hazards

Mitigation - Identification

Mitigation – Identification

•Studying aerial photographs to determine previous landslides

•Field investigations of potentially unstable slopes

Mitigation - Prevention

•Steep slopes can be graded into gradual slopes• Retaining walls can be built

•Drain pipes to reduce pore water