What is Mass Wasting?What is Mass Wasting?

Rapid types

Slow types

Selected LandslidesDATE LOCATION TYPE DEATHS 1556 China Landslides-earthquake triggered 1,000,000 1806 Switzerland Rock slide 457 1920 China (Kansu) Landslides-earthquake triggered 200,00019631963 Italy (Vaiont Dam) Italy (Vaiont Dam) Landslide-subsequent flood Landslide-subsequent flood 2,000 2,000 1966 U. K. (Wales) Debris flow-collapse of mining-waste 144 1970 Peru (Mt. Huascaran) Rockfall & debris avalanche 25,000

earthquake triggered 1972 USA (WV) Landslide & mudflow-collapse of 400

mining-waste 1979 Indonesia (Sumatra) Landslide 80 1980 USA (Washington) Avalanche and mudflow 63 1989 Tadzhikistan Mudflow-earthquake triggered 274 1996 Brazil (Recife) Mudflow 49 1999 Venezuela Mudflow 10,000

Why Should You Study Mass Wasting?

• Shear strength of slope mat.

• Angle of repose

• Gravity

3 Factors Influencing Mass Wasting:

Gravitational forces exceed resisting forces

Dynamic equilibrium

5 Causes of Mass Wasting:

Slope Angle {Steep slope = _________ stability}

Oversteepening slopes:

• Highway excavations remove support often resulting in slope failure.

Pan-American Highway, Mexico

Weathering & Climate

• Weathering decomposes & disintegrates rock, ____________shear strength & ____ mass wasting.

• Mass movement ______________ in deeply weathered material. (prevalent in tropics)

• Deserts Lack of vegetation (_______________) & cloudbursts frequently produce rapid mass wasting (i.e., mudflows).

Water ContentSlope stability

How does water affect slope stability?

Vegetation

Golden State Freeway,1987

Overloading…

• Under natural conditions, a slope’s load is supported by friction of grain-to-grain contacts w/in slope material.

• Overloading __________________________________ w/in slope material.

• Dec. shear strength

Triggering Mechanisms

Most common:Most common:

In highly unstable slopes:

La Conchita, Ca.1995

Types of Mass Movements

FallsRockfalls

SlidesSlumpRockslides

FlowsMudflowDebris flowEarthflowCreep

Complex movements

Rockfalls: (_________________________)

Slopes are sometimes covered w/ wire mesh to reduce the hazard.

Hawaii

Slides

Slumps

Rock slides

A B

Flows

Earthflows

Baraga, Michigan

Mudflows

Debris flows

Estes Park, Colorado

Creep

Effects:

Marathon, TX

Complex movements {combo of several types}

Debris avalanches

1970 killed 25,000 in Yungay & Ranrahirca

Peru, 1970

• Geologic investigation identifies

• Analysis of a material’s properties (composition, susceptibility to weathering, cohesiveness, & ability to transmit fluids)

(Info is used to assess risks before construction begins.)

Recognize & Minimize Effects of Mass Movement

DewateringDewatering

Ways to dewater:

• Perforated drainpipes inserted horizontally into slopes are used to reduce the amt of water w/in slope material.

Pt. Fermin, CA

Cut-and-Fill method

How Can We Minimize Mass Movement?

Benching

How Can We Minimize Mass Movement?

Retaining walls

Most successful when:

How Can We Minimize Mass Movement?

Rock bolts

How Can We Minimize Mass Movement?

Brisbane, Aust..