Chapter 8 - Mass Wasting

Mass Wasting

Is the movement of material (rock or soil) down slope due to gravity.

Mass movements owing to downslope pull is called

Shear Stress

The steepest stable slope that an unconsolidated material can maintain is the material's

Angle of repose

An over steepened slope

Is one that has an angle greater than the angle of repose for the material comprising the slope.

Addition of water to soil on slopes may

Destabilize the slope by reducing frictional resistance to sliding.

Rock falls

Occur on any steep-faced cliff, including under waterfalls.

Slumps are characterized by

Somewhat coherent pieces of earth that rotate on a curved surface.

Quick clay is

A marine deposited mixture of glacially derived clay and silt weakened by infiltrating fresh water upon uplift of these sediments above sea level.

Unconsolidated material is likely to be involved in which kinds of mass movement?

Creep, slumps and avalanches

The coarse material that gathers at the foot of the slope which results in rockfalls is called

Talus

Debris flows

Both may move rapidly and transport rock materials of greatly different size and are common in semi-arid regions are correct.

This type of mass wasting is a hazard within Yosemite National Park

Rock slides and rock falls

Which of the following is the slowest form of mass movement?

Soil Creep

Which of the following is the fastest form of mass movement?

Rockfall

When wet soil moves slowly over an impermeable surface the phenomenon observed is called

Solifluction

All of the following could increase the risk of landslide on a slope except

Planting shrubs with extensive root systems.

The type of clay that can absorb water up to twenty times its weight and results in the formation of a weak gel is

Montmorillonite.

Vegetation may

Increase slope stability because roots help hold soil in place. Decrease slope stability by adding weight.

Increase slope stability by taking up moisture.

Construction of a reservoir behind a dam

Can destabilize the slopes by increasing pore fluid pressure.

Soil creep

Is more of a hazard to property than to lives.

The reason clay minerals (and other phyllosilicate) often form the slip plane for a landslide is that they

Have platy structures, allowing them to stack up and then slip past each other, like a deck of cards and also have high porosity.

Quick clays are characteristically found in

Northern polar regions.

Rainfall intensity and duration affect the likelihood of the occurrence of mass movement. Which of the following is true

They are both important, but different geologic materials and geographic settings have different resistance to mass movement as started by rainfall.

A kind of mass movement in which materials move in a disorganized, chaotic fashion is a

Flow

Where rotational movement of soil is accompanied by downslope movement the feature that is observed is a

Slump

Which is/are true?

*Curved tree trunks and tilted utility poles may be signs of soil creep

*In a true slide, movement of a coherent mass of material occurs along a well-defined plane

*Surfaces of ancient landslides often have a lumpy (hummocky) appearance

What is the most important process for the loosening and braking up of consolidated rock in high, mountainous regions?

Repetitive freezing of water and thawing of ice in cracks

In designing a retaining wall to support an unstable slope, the best design would be

A short, stout wall at the foot of the slope.

A thin, shallowly inclined rockslide might best be stabilized by

The use of rock bolts.

If a slope in unconsolidated material is unstable due to high water content,

It may be dewatered by installation of drainage pipes.

Which of the following is/are true?

An unstable slope can be stabilized by removing material to reduce the slope angle.

A landslide warning system, developed in California, utilizes all of the following except

Laboratory studies of response of slopes to earthquakes.

Factors contributing to the Vaiont Reservoir landslide included all of the following except

Earthquakes.

Which of the following is a common "trigger" of landslides?

Earthquakes

Reduction of the slide potential of a very steep slope can be carried out by

Placing more support on the foot of the slope.

Reducing the weight or loan on the slope Reducing the angle of the slope.

Weathering process do exert some influence on mass wasting.

True

Localized areas of high landslide risk may occur within regions of overall low risk

true

Mass wasting is possible anywhere in the world, either due to natural processes or human modification.

True

The removal of vegetation always makes soil-covered slopes more stable because it removes excess weight.

false

The light weight of snow, as compared with soil or rock, means that snow avalanches are never a threat to property.

false

Landslides may be triggered by earthquakes or by heavy rains.

True

Mass wasting threatens only property, not lives, because it occurs so slowly.

False

In a true slide, movement of a coherent mass of material occurs along a well-defined plane.

True

A secondary hazard of landslides is flooding that occurs when slides dam stream valleys.

True

Sites of past rock falls or slides are sometimes obvious because they remain unagitated.

True

. Human activities do not play a role in mass wasting.

False

Once poor land-use practices causing landslides are halted, the slides will also stop moving.

True

A landslide warning system recently tested in California could identify the areas at risk, but could not predict the time of probable sliding.

True

In landslide-prone areas, whether a given rainstorm will cause sliding may depend, in part, on the amount of rainfall in the recent past, too.

True

Landslides never take lives because they move slowly.

False

In the Vaiont Reservoir disaster, flooding resulted when water rushed over the dam due to a large landslide.

True

. Heavy rains and thick tropical soils caused landslides and debris flows along the Venezuelan coast.

True

Rock falls and rock slides occur in Yosemite National Park because slopes over steepened by past glaciations are readjusting to lower, safer slope angles.

True