Geol 9 Chapter 15 - Mass Movements

What type of mass movement is shown here?

Subsidence

What do you need to know in order to calculate the downhill force of an object?

The degree of the slope Mass of the object

Why does the ground surface of a slope move up and down?

The soil is constantly swelling and shrinking.

Why is water so easily adsorbed onto the surface of clay minerals?

The water molecule is bipolar, with a positive charge on one side and a negative charge on the other. The surfaces of clay minerals have a negative charge.

Which of the following can act as both an internal and external factor in slope stability?

Water

When pressure is applied to a pile of sediments, the grains will pack together more tightly, taking up less volume. Water, however, simply stores the pressure. Why is this?

Water is nearly incompressible.

Rockfalls are common in the steep granite valleys of _______ National Park in California. In July 1996, 2 huge slabs of rock first slid and then were launched 500 meters in the air before hitting the valley floor.

Yosemite

The block slide event in 1920 near Point Fermin, California, is believed to have been primarily caused by _______.

an excess of water from landscape irrigation

This mass movement event, which occurred near Point Fermin in California, is an example of a _______. In 1929, a half-mile long segment of the coast slid slowly seaward along inclined bedding planes. The slipping material remained largely intact.

block slide

The Swedish circle analysis is used to _______.

calculate driving versus resisting forces for a mass of material on a curved slip surface

We can use simple netting and wattles to help ______ in order to mitigate damage from mass movements.

control erosion

The fact that much of the central and southeastern United States is underlain by limestone tells us that this region was once _________.

covered by warm, shallow oceans

The slow, almost imperceptible downslope movement of soil and the uppermost bedrock zones is called ______.

creep

Rock layers that dip at angles less than that of a hillslope will be exposed on the slope surface. These layers, known as _______, are unstable because there is no support at their ends that will hold them back from sliding.

daylighted bedding

This mass movement event that occurred on Interstate 40 in North Carolina is an example of a ______. This is clear from the large slabs of broken hard rock that are lying on top of the layer of softer sedimentary rock.

debris slide

Removing the tops of hills can reduce the likelihood of landslides because it ______.

decreases the driving mass

Water can weaken a rock by ______ minerals that form the rock's cement.

dissolving

The netting shown in this image was placed on the slope to reduce _______ and allow plants to grow.

erosion

As clay minerals take in or lose elements and water from their crystalline structure, they will ________. This can significantly weaken a slope.

expand and contract

When engineers cut into the base of a slope to make way for a new road, this is an example of a(n) ______ process that increases the likelihood of slope failure.

external

The steep-sided walls of Yosemite Valley are made of granite that contains multiple sets of joints. This makes the valley prone to _______ events.

fall or rockfall

Mass wasting that involves the material moving downslope as a viscous fluid is called a ______.

flow

_______ a type of retaining wall made of rocks held in place by steel cables.

gabion

Removing earth to lessen the steepness of a hillslope will reduce the pull of _______, thus lessening landslide hazards.

gravity

The law of ________ states that two bodies are attracted to each other with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

gravity

The inherent weaknesses of the materials making up a hillside are collectively thought of as ______ factors controlling slope stability.

internal

The removal of groundwater or oil can result in subsidence because ________.

it reduces pore-fluid pressure, allowing for compaction of the sediments

Rock falls are common from cliffs made of rocks that contain _______.

joints and fractures

The 1964 mass movement in Turnagain Heights, Anchorage, Alaska, is an excellent example of a _________, because it involved the failure of weak clays at depth. These clays liquefied and flowed, causing the breakup of the overlying, more coherent layers.

lateral spread slide

The mega-boulder that destroyed this house is an example of a(n) ______ event.

mass movement

When the water table rises, there are _______ mass movements.

more

When a slump occurs, the head of the slide will typically _____.

move downward and rotate backward

When a slump occurs, the toe will typically ________.

move upward and outward

Caves form in limestone when ______.

naturally acidic groundwater dissolves the carbonate rock

Subsidence between Houston and Galveston, Texas, due to the extraction of ______ caused part of the coast to be submerged by seawater from San Jacinto Bay.

oil

When sand grains become supersaturated with pressurized water, the water can push the grains apart, leaving them with no strength. When this water-pressurized sand forms on a flat surface or in a depression, it becomes _______

quicksand or liquefied

The landslide mitigation method shown here is a _______ _______

retaining wall

During heavy rains, the water table will ______, which can trigger slope failures.

rise

Daylighted bedding, as shown this image, occur when ______.

rock layers dip at angles less than the hill of the slope

The Ensenada, Baja California, slump or ______ slide, that occurred in 1976 carried part of Highway 1 into the ocean and uplifted part of the ocean floor.

rotational

A _______ is a type of mass wasting in which the descending mass remains relatively intact and moves along a curved slip surface.

rotational slide

The 1976 mass movement event in Ensenada, Baja California, that carried a long portion of Mexican Highway 1 into the Pacific Ocean, is an example of a _______.

rotational slide

The melting of frozen pore water and the drying out of clay minerals are two mechanisms that cause soil to ______.

shrink

The ground surface moves up and down because it swells and _______ due to several processes.

shrinks

When the roof of a cave collapses, a ________ can form.

sinkhole

A _____ is a type of mass wasting in which the descending mass remains relatively intact and moves along a well-defined surface.

slide

A rotational slide is a slide that occurs on a curved surface. It is also commonly known as a(n) _______

slump

The downward movement of the ground surface due to compaction or cave collapse is called _______

subsidence

The downward movement of the ground surface due to compaction or cave collapse is called ________

subsidence

(Gx Mass 1x Mass2) / (distance x distance) is ______.

the law of gravity

A flow is distinguished from a slide in that _________.

the material in a slide remains relatively intact, whereas the material in a flow moves as a viscous fluid

Sinkholes, such as the one shown here, are common in central Florida because _______.

the region is underlain by limestone

Overpressurized pore water in a pile of sediments can cause slope failure because ________.

the water will start to move upward, lifting the sediments with it

When water fills the pore spaces in soil and sedimentary rocks, ________, which can destabilize a slope.

the weight of the material is increased dramatically

Block slides, debris slides, and lateral spreading are three of the different ways in which _______ slides behave.

translational

Underlying conditions, such as structural weaknesses, will push a slope to the brink of failure. It takes a _______ , such as an earthquake, to make the slope fail.

trigger

Heavy rains, earthquakes, and construction projects can all be _______ for mass movements.

triggers

An important landslide mitigation technique is the reduction of the amount of _____ in a slope.

water

Because it can both add weight and reduce friction in a slope, draining _______ is a common way to reduce the danger from mass movements.

water

Sedimentary rocks often have porosities of up to 30%. When the pore spaces are filled with _____, the downward force on the slope increases, which can lead to slope failure.

water

Slow subsidence of the land surface occurs when _______.

water or oil are pumped from below the ground

Joints, faults, and a lack of cement are all ______.

weaknesses in rocks that increase the probability of a slope failing

Which of the following would be indicators that creep is occurring on a hill slope?

Bedrock layers deformed downslope Telephone poles leaning downslope Bent tree trunks

Clay minerals can be weakened either when they _______ water (incorporate it into their mineral structures) or when they _______ water (bind it onto their crystal surfaces). This can destabilize a slope.

Blank 1: absorb Blank 2: adsorb

The top of a landslide is the _______ and the bottom is the _______.

Blank 1: head Blank 2: toe

Caves form in ________ rock when _______ water flows through fractures, dissolving the rock.

Blank 1: limestone Blank 2: acidic

_______ _______ are used to strengthen a rock mass and reduce landslide hazard.

Blank 1: rock or swellex Blank 2: bolt

The two types of slide are ________ slides, which occur on curved slip surfaces, and ______ slides, which occur on planar surfaces.

Blank 1: rotational or slump Blank 2: translational

A _______ _______ is a type of mass movement in which the descending mass remains relatively intact and moves along a well-defined plane that is approximately parallel to the slope of the surface.

Blank 1: translational, block, or rock Blank 2: slide

True or false: Rotational slides tend to travel farther than translational slides.

False Reason: The arcuate motion of a rotational slide tends to limit the distance it will travel.

Which of the following processes cause soil to swell?

Freezing of water in pore spaces Solar heating of the surface Absorption of water by clay minerals

_______ is the resistance to motion of a body that keeps it from moving over another body.

Friction

Which of the following are common triggers for mass movements?

Heavy rain Construction projects Earthquakes

________ is the tendency of a body to remain at rest until an external force is applied.

Inertia

Why did the St. Francis dam fail in 1928, only two years after it was built, causing the death of about 420 people?

Lake water dissolved the cement that held together the rocks below the base of the dam, causing them to fail.

What should you do if you get caught in quicksand?

Lie back and spread your arms.

______ is a rock formed in warm, shallow seas from the shells and skeletons of organisms. It is composed of the mineral calcite (calcium carbonate).

Limestone

The large-scale transfer of material downslope under the pull of gravity is called _______ _______

Mass Movements

Which of the following are types of flow?

Mudflow Creep Debris flow Debris avalanche

Which of these is an example of water acting as an external factor in decreased slope stability?

Rain runoff

Which of the following are external processes that increase the odds of a slope failure?

Rain runoff Slope steepening Addition of mass high on a slope Removal of lower slope support

Which of the following are consequences of groundwater pumping in Houston?

Renewed movement on old faults Subsidence

The debris slide that occurred on October 25, 2009, on Interstate 40 in the Great _______ Mountains blocked the freeway for 6 months.

Smoky

Which of the following are used to classify different types of mass movement?

Speed of movement Water content

Which of the following best describes the structure of clay minerals?

Stacked parallel sheets

The downhill force acting upon an object can be calculated using the mass of the object and the angle of the slope it lies upon. The downhill force is equal to the mass of the object multiplied by the sine of the slope angle. Examine the example shown here for a boulder with a mass of 1 lb { 1 x sine30 = 0.5 }. What would be the downhill force of a boulder with a mass of 5 lb on a slope with an angle of 30?

2.5 lb

Which of the following are rock structures that set-up slope failure?

A layer of clay Alternating soft and hard rock layers Joints, fractures, and faults

Which of the following is the best description of the relationship between a cause and a trigger for slope failure?

A trigger is the immediate cause for the failure of an already weak slope.

Which of these are strategies for preventing mass movements?

Addition of rock bolts Removal of material from the top of a slope Construction of retaining walls

What triggered the 1964 lateral spread slide in Turnagain Heights, Anchorage, Alaska?

An earthquake

What is the slowest but most widespread form of slope failure?

Creep

Which of the following are considered to be internal causes of slope failure?

Decreasing cohesion Adverse geologic structures Pore water Weak rock