Mass Wasting (aka landslides)

3 types of mass wasting:

1. Flow2. Slide3. Fall

Flow - moving mass is a viscous fluid

Types of flows

• Creep• Earthflow• Mudflow• Debris avalanche/rock avalanche

Fast

!

S

low

Creep• Downslope

movement of soil or debris

• Moves <cm/yr• Can be

caused by freeze/thaw

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Types of flows

• Creep• Earthflow• Mudflow• Debris avalanche/rock avalanche

Fast

!

S

low

Earthflow

• Thick cover of debris

• Happens after heavy rain with saturated soil

• Characteristics: scarp, hummocky toe

Types of flows

• Creep• Earthflow• Mudflow• Debris avalanche/rock avalanche

Fast

!

S

low

Mudflow

• Mix of debris and water• Usually in a stream channel• After a heavy rainfall• Moves slower than water, but can carry

boulders• No vegetation• Young volcanoes

13A volcano like this (this one is in Alaska) can produce a...

..mudflow like this.

15Dried mudflow in the Andes

16Bridge washout after Mt.St.Helens

Types of flows

• Creep• Earthflow• Mudflow• Debris avalanche/rock

avalancheFast

!

S

low

Avalanches• Debris or Rock avalanche

– Turbulent mass of debris, rocks, air, water

– 100s km/hr – Forms an air cushion

• Example? Yungay, Peru 1970

19

20

Right after

5 years later

Slide - moving mass remains intact

Slump!

Fall - moving mass free falls!

A fall can happen when:a) frost wedging, b) undercutting

Talus: fallen rock fragments

Talus!

27Rockfall in Yosemite!

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So wear a helmet!

What controls the likelihood & rate of mass movement?

1) Slope angle: Increase slope,

What controls the likelihood & rate of mass movement?

1) Slope angle: Increase slope, increase movement

What controls the likelihood & rate of mass movement?

1) Slope angle: Increase slope, increase movement

2) Topographic relief:

Increase relief,

What controls the likelihood & rate of mass movement?

1) Slope angle: Increase slope, increase movement

2) Topographic relief:

Increase relief, increase movement

What controls the likelihood & rate of mass movement?

1) Slope angle: Increase slope, increase movement

2) Topographic relief:

Increase relief, increase movement

3) Thickness of debris over bedrock

Increase thickness,

What controls the likelihood & rate of mass movement?

1) Slope angle: Increase slope, increase movement

2) Topographic relief:

Increase relief, increase movement

3) Thickness of debris over bedrock

Increase thickness, increase movement

What controls the likelihood & rate of mass movement?

4) Orientation of bedding planes in bedrock:

What controls the likelihood & rate of mass movement?

4) Orientation of bedding planes in bedrock:

Perpendicular to surface good, parallel bad

What controls the likelihood & rate of mass movement?

4) Orientation of bedding planes in bedrock:

Perpendicular to surface good, parallel bad

5) Ice/water/ precipitation

What controls the likelihood & rate of mass movement?

4) Orientation of bedding planes in bedrock:

Perpendicular to surface good, parallel bad

5) Ice/water/ precipitation

More liquid=more lubrication! Little water good, lots bad

What controls the likelihood & rate of mass movement?

4) Orientation of bedding planes in bedrock:

Perpendicular to surface good, parallel bad

5) Ice/water precipitation

More liquid=more lubrication! Little water good, lots bad

6) Vegetation Increase vegetation,

What controls the likelihood & rate of mass movement?

4) Orientation of bedding planes in bedrock:

Perpendicular to surface good, parallel bad

5) Ice/water precipitation

More liquid=more lubrication! Little water good, lots bad

6) Vegetation Increase vegetation, decrease movement

Prevention #1

• Control & take better care in construction

• Add vegetation

Prevention #2• Add retaining walls & drain pipes

Prevention #3• Avoid oversteepening slopes & pay attention to bedding planes

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Sea-to-Sky highwayVancouver-WhistlerWinter 2008

Prevention #4

• Rock bolts

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Or cover the wall in chain link fence!