GEO week 6
On average, how much damage do mass wasting problems cause in the United States annually?
$1-2 billion dollars and 25-50 deaths
In 1970, a mass wasting event in Peru killed an estimated ______ people who were living in the flat terrain at the base of a hazard zone. Several generations had passed since the last major event, so the threat was a distance memory.
18,000
What is the maximum angle to repose for unconsolidated sediments?
30°-35°
Match the survival rate of people trapped in snow avalanches with the situation.
90% = Dug out of snow within 15 minutes 30% = Dug out of snow after 45 minutes
What is a lahar?
A mudflow of volcanic ash caused by heavy rains or melting ice or snow
What is a bedding plane?
A sheetlike layer of rock or sediment that represents a transition of materials that is structurally weak.
What is terracing?
A slope stabilization method in which a series of flat benches are created on a hillside
Which of the following are clues of recent mass wasting?
A swath of downed trees Piles of rocks and other debris at the base of a slope An area that is bare or covered by little vegetation within a larger region that is covered by vegetation
Identify specific methods of covering slopes or adding specific materials that are used to increase slope stability.
Adding crushed rocks to the surface of the slope Covering a slope with a synthetic mesh Adding fast-growing plants with sturdy root systems to a slope
Match the type of climate to common scenarios of mass wasting.
Arid climates = Vegetation is unavailable for absorbing rain, which causes mass wasting. Temperate climates = Higher-than-average rainfall saturates soil until friction is overcome and material moves. Cold climates = Freeze-thaw cycles cause material to move downslope slowly.
Which types of material does gradual subsidence generally occur in?
Clay sediments Sand Sedimentary rocks
Which of the following are covering methods used to increase slope stability?
Covering with mesh or fabric Planting vegetation
Which of the following describes the process of creep movement in soils?
During expansion, soil particles are moved upward, and during contraction, they move downward. This process is imperceptible.
Which of the following are the most common trigger mechanisms for mass wasting?
Earthquakes Wildfires Heavy rain
Why is there development and/or human settlements in areas known to be at risk from mass movements?
Economic pressure for more development can override the concern caused by the threat of mass wasting. In some areas, there may be little land not at risk from some natural hazard. Development may have existed before the risk was well understood.
transpiration
Evaporation of water from the leaves of a plant
How are fall events and freeze-thaw cycles related?
Expansion of freezing moisture in fractures wedges apart rocks until they break loose and fall.
How is snow stabilized for recreational use, such as at ski resorts?
Explosives are use to initiate snow avalanches and reduce the total load of snow.
Which of the following accurately describe the mass wasting motion called a fall?
Falls composed mostly of rock are called rockfalls. It involves a free-falling action in which the moving material is not always in contact with the ground.
What might be the best option for slope stabilization in this image?
Fill the mass wasting area with fill material and engineer a retaining wall below the road.
Order these material types by how steep of a slope they can form. Place the material forming the steepest slope at the top and the material with the flattest slope at the bottom.
Granite with tight crystal formation Sedimentary rocks with various mineral compositions Unconsolidated sediment
Which of the following are processes that influence mass wasting in regions with volcanic activity?
High temperatures Seismic activity Weathering by gases and fluids Reduced vegetation
Which of these causes is believed to be the source of repeated landslides on the volcanic Mount Rainier?
Internal breakdown of rocks
What is the mass wasting movement known as creep?
It is an imperceptible slow, downslope motion of earth materials.
What is mass wasting?
It is the collective term used to describe all downslope movement of earth materials caused by gravity.
How did the construction of the highway lead to slope failure?
It oversteepened the slope.
Which of the following slope stabilizing methods are best used on unconsolidated materials?
Modifying slope geometry Covering a slope with Portland cement Drying unstable soil by diverting water away from it
Which of the following are key risk factors that identify general mass wasting hazards?
Oversteepened slopes Materials with high water content Unconsolidated materials on slopes Weak planes parallel to slopes
Which of these reasons can be attributed to the loss of an estimated 18,000 people from a mass wasting event in 1970 in Peru?
People were living in the easy-to-develop, flat terrain at the base of a hazardous area. Many generations had passed since the last major mass wasting event.
Order the steps in a process of a slope becoming unstable due to heavy rains. Put the first step at the top and the last at the bottom.
Precipitation begins. Water infiltrates the soil. Water reaches a low permeability layer. Voids in sediment fill with water. Pore pressure begins to push outward. Material loses friction and begin to slide.
Which of the following are prevention techniques for avoiding damage from collapsed sinkholes?
Prevent surface water from infiltrating Limit large withdrawals from the water table Restrict building over large cavities
Which of the following are often triggers of sudden, rapid landslides?
Rapid melting of abundant snow Heavy rainfall Earthquakes
Which of the following are applications for terracing?
Reducing mass wasting risk Agricultural terrain
How do human activities influence slope stability?
Removing vegetation decreases slope stability. Highway roadcuts decrease slope stability.
What is an effective placement of retaining walls?
Retaining walls should intersect the plane of movement.
Which of the following might be included in a debris flow?
Sand Boulders Water Vegetation
Match the types of sediment to the relative angle of repose the material could form if it were in a naturally formed pile.
Saturated sediment = Little to no angle Sediment with angular grains = High angle of repose Sediment with rounded grains = Low angle of repose
Which of these factors or conditions can cause mudflows or debris flows?
Saturated soils Sparse vegetation
What processes are involved in slope failures caused by heavy rain events?
Saturation of pore spaces Decrease in friction and cohesion within the materials
How do earthquakes influence mass wasting?
Seismic waves vibrate slope materials, decreasing frictional forces. They are a common trigger of mass wasting.
How does a karst landscape form?
Sinkholes collapse, creating an area covered in shallow depressions.
Which of the following are trigger mechanisms for a snow avalanche?
Skiers or snowmobilers Heavy accumulations of fresh snow Surface melting of snow
Which of the following accurately describe the mass wasting movements known as slides?
Slides involve a single unit or rock or soil slipping downward along a clearly defined surface or plane. Most rockslides occur along planes or bedding surfaces between rock layers.
What is the name of mass wasting events that involve snow instead of rock or sediment?
Snow avalanches
Which of the following accurately describe the mass movements known as flows?
Snow avalanches are a kind of flow. Common flows involve fine-grained sediments and water called mudflows. The downslope movement of material behaves like a fluid.
Gravity is always acting on sediments and rocks. Which of these factors influences gravity's ability to move material down slope?
Steepness of the landscape
What purpose do stream cutbanks serve?
Stream cutbanks are part of an undercutting process that widens valleys as streams migrate from side to side.
When rocks fall from hillsides or cliffs, they form a talus slope at the bottom of the valley. How are these rocks removed from the valley so it does not fill in with loose rubble?
Streams generally weather or carry away rocks.
Which of the following describes the use of protective structures to deal with threats posed by mass wasting?
Structures are built so earth material can just flow or slide over the shelter instead of the protected area. The method does not work if the land the shelter would need to be built on is also moving.
Which of the following are accurate with regards to the role of fluids in mass movements?
The addition of some moisture to dry soils may increase the soil's adhesion, making mass wasting less likely. The addition of fluids to a body of geological materials increases its mass, making mass wasting more likely.
Which of these best explains the relationship of vegetation to slope stability?
The complex relationship between vegetation & slope stability depends on vegetation density, precipitation intensity & slope water content.
Which of the following accurately describe the use of rock bolts to stabilize a rocky slope?
The method generally works when the weakness planes are oriented in the same direction as the slope. Rock bolts have been proven to work in tunneling and mining.
What is solifluction?
The slow movement of wet soil over permafrost
How is a slump supported so that it is somewhat stable?
The toe of the slump stabilizes the mass.
Which of the following movements are classified as mass wasting?
The vertical collapse of soil and rocks down a sinkhole A rapid movement of unconsolidated rocks down a cliff A slow, subtle creep of soil down a gentle slope
On what basis are mass movements classified?
The way material moves downslope The type of material moved
Under what circumstances are retaining walls used?
They are used when a flat surface is needed in sloping terrain for development.
Which of the following accurately describe the mass wasting movements known as slumps?
They involve a downslope motion of materials that often includes a curving component in which the top layer is relatively undisturbed. The toe of the slump may transition into a flow at its bottom.
How do plants influence mass wasting events?
They remove moisture from soil and in doing so increase friction up to a point. They add weight to the mass of soil, increasing the weight on a slope. Their roots can provide a strong, interlocking network that binds particles together.
Which of the following are trigger mechanisms for submarine mass wasting events?
Tsunamis Hurricanes Seismic activity
How can submarine mass wasting effect life above the ocean?
Tsunamis can be triggered. Oil and gas lines can be damaged.
In which of these situations are rock bolts commonly used?
Tunnel ceilings Rock walls Cliff faces
Which of the following are ways caves are formed?
Underground mining of minerals Draining of magma from a chamber Groundwater circulating through soluble rock
How should water be managed on slopes to maximize stability?
Water should be diverted from slopes to prevent accumulation of moisture.
Match the letter to the correct force acting upon the rock on this slope.
a = Friction (shear resistance) b = Shear force of gravity c = Gravity d = Perpendicular force of gravity
The maximum slope angle at which unconsolidated material can be piled and remain stable is called the _____ of ______
angle; repose
The weak planes that develop between different layers of snow in the mountains makes them susceptible to ______
avalanche
What force is getting larger as the slope gets steeper?
b - shear force of gravity
Any process that quickly adds weight, decreases friction, or increases pore pressure in earth materials can ______ mass wasting.
be a trigger causing
Sediment and sedimentary rocks contain ______ planes, which represent a change in the deposition process. They are weak zones and prone to splitting or breaking along those surfaces.
bedding
When water circulates through soluble rock, minerals dissolve and leave behind voids known as ______.
caves
When sediments contain ______ minerals, the sediments may behave plastically. These minerals can greatly reduce friction between grains when they take on ______ and begin to flow.
clay; water
This image shows how individual grains of soil move in order to produce ______ as soil expands and contracts.
creep
Valleys become wider when meanders in rivers form ______ as they undercut stream banks. Over time, this erosion removes material from both sides of the stream, slowly widening the valley.
cutbanks
A type of flow consisting of a wide range of materials from fine sediments to rocks and trees is called a _____ flow.
debris
What type of mass wasting event occurred on Leyte Island in the Philippines in 2006 after a period of heavy rains?
debris slide
As slope increases, the component of gravity pulling ______ becomes more dominant.
downslope
Landslides and debris avalanches are often triggered by ______ as the energy from them stresses and fractures earth materials and jars apart soil and rock masses.
earthquakes
The mass wasting movement called a(n) ______ involves the free-falling action of material that is not always in contact with the ground; these movements often include rocks, but other materials can be involved as well.
fall
True or false: Debris flows are limited to a specific geologic setting of volcanic soils and climate setting in arid environments.
false
True or false: The 2014 Oso, Washington, deadly slump event was a complete surprise to scientists and engineers.
false
The mass movement involving surface materials moving continuously and turbulently downslope is called a(n) ______.
flow
During a snow avalanche, the slab breaks into smaller and smaller pieces. The mass moves like a ______ with a density ______ that of the human body.
fluid; less than
A landslide is a ______.
general term for the result of a rapid mass movement of geological materials
Pumping large quantities of water or oil from reservoirs below the surface reduces pore pressure between grains. This is the leading cause of ______ land subsidence.
gradual
In Texas, _____ subsidence of up to 10 feet has been caused by withdrawals of water and ______. The new lower elevation of the land has increased the frequency and intensity of flooding.
gradual; oil
Movement of rock and sediment occurs when the force of ______ is stronger than the forces that hold the material in place.
gravity
Which of these factors influences the appearance of Earth's surface by working to soften the rough terrain created through tectonic activity?
gravity
After the 2006 slide on Leyte Island in the Philippines, researchers concluded that ______ from four days prior caused the event. Multiple choice question.
heavy rain
Both small and large scale mass movements at La Conchita, California, have been triggered by ______.
heavy, seasonal rains
Investment in prevention, management, and mitigation of mass wasting contradicts the issue that much of what is being stabilized, reinforced, or restored has been caused by _____ action in the first place.
human
Recent mass movements at La Conchita, California, have ______.
included slumps, earth flows, and debris flows
When a thin film of water forms within the pore space between sediment grains, electrical forces act to ______ sediment cohesion.
increase
Which of the following best describes the role of fluids in mass wasting? Generally, the addition of fluids to geological materials ______.
increases the likelihood of mass wasting, although dry soils and sand may become more stable when some moisture is added
The 2014 Oso, Washington, mass wasting tragedy ______.
involved glacial sediments was a debris slide and flow
A climate that has dry summers with wildfires followed by winter rainy season ______.
is likely to have mass wasting because the vegetation is removed
The general term for all downward movement of geological materials due to the force of gravity is _____ ______
mass wasting
The movements in landslides, rockslides, and avalanches, and the collapse of sinkholes are all examples of ______.
mass wasting
Which preventative method should be used when engineering stabilization methods are expected to be very costly?
material removal
Mass wasting hazard maps showing high-risk areas can be used to ______ activities that trigger mass wasting events.
minimize
A common method of spreading seed over a bare slope is called hydroseed, which is a slurry mixture containing ______. The mixture immediately helps reduce surface erosion, helps seed sprout, and stabilizes top soil with grass roots.
mulch seeds fertilizer
Subsurface materials are capable of maintaining pore spaces, open fractures, and voids so long as the ______ pressure does not exceed the strength of the rock or sediment.
overburden
When sediment on a slope becomes saturated, what force repels the grains from each other and can cause slope destabilization?
pore pressure
Engineering controls applied to mass wasting aim to minimize hazards to humans and development. The first approach to this goal is to _____ movement. The second approach is to provide ______ from movement that is inevitable.
prevent; protection
Restricting development and reinforcing weak slopes are two _______ methods used to avoid damages from mass wasting events. These two methods cost significantly less than the cost of the possible damage.
preventative
A _______ wall is an engineering structure that is used to strengthen oversteepened slopes.
retaining
Most of the talus that builds up from falls at the base of steep cliffs is carried away by ______ rather than remaining and ultimately filling up the valley with debris.
rivers glaciers
The fairly cohesive movement of a unit of rock or soil as it slips down a clearly defined surface or plane is called a ______.
slide
Construction and development activities in sloped terrain cut away at material to make flat areas. This often results in oversteepened ______ that are unstable both above where material has been ______ and below the cut where material has been piled.
slope; removed
A jumbled-looking, downslope motion of earth materials that typically includes a curving movement is called a ______
slump
Mass wasting known as ______ includes sliding and flowing, and is problematic to deal with because once movement has begun, it is nearly impossible to stop. When the toe of these slopes are removed, the material above is left unsupported.
slump
A ______ can reach speeds of up to 80 miles per hour. While flowing, it has a liquidlike consistency and a low density that people can "swim" through. Once this flow stops, the mass almost immediately solidifies into something as hard as concrete.
snow
What is the name of the special type of creep that occurs in very cold climates and involves permafrost?
solifluction
Rocks with minimal weathering are capable of forming ______ slopes, whereas rocks with more advanced weathering form ______ slopes.
steep; gentle
Traps, diversions, and shelters are all protective _____ that are employed when using physical stabilization methods are too costly or too dangerous.
structures
Earthquakes, hurricanes, or tsunamis can be trigger mechanisms for ______ mass wasting.
submarine
Gradual _____ occurs when clay minerals are forced to align in a parallel manner and the material becomes more compact.
subsidence
The lowering of the land surface due to the closing of void spaces, large and small, is called ______
subsidence
Earth's topographic relief is created by _____ activity, whereas the physical force of ______ causes many processes that wear down Earth's rough surface.
tectonic; gravity
The clues present in this diagram indicate ______.
the soil is slowing creeping down the slope
Processes called ______ mechanisms reduce the frictional forces on a slope and increase the effect of gravity, which puts the slope at a much higher risk for downslope movement.
triggering
When the top layer of snow melts, refreezes, and is then covered with fresh snow, a _____ layer forms between the old and new snow. This layer is covered in a thick slab of coherent snow prone to ______
weak; slide
The expansion of rock fractures as moisture freezes is called frost ______ and is caused by the increase in volume that occurs as water freezes. This expansion drives rocks apart and makes them susceptible to ______.
wedging; rockfalls
