Geology - Chapter 15 HW
When dry sediment accumulates, the angle of repose represents what property of the deposit?
The steepest angle at which those sediments can accumulate and remain stable.
How might a wildfire influence mass movement?
Wildfire destroys plants which anchor soils and loosen upper layers of soils, increasing mass movement events.
The Gros Ventre slide is evident today by _______________.
a scar, runout area, and landslide debris filling the valley
When large rocks become dislodged and drop down a steep slope, the mass movement is called a __________.
fall
Which of the following are classifications describing how rock and other material move downslope?
fall, slide, slump, creep, flow
When unconsolidated material moves downslope as a viscous fluid it is called a _________.
flow
Which type of mass movement event requires the addition of water?
flow
What ways material can move during mass movement events?
flow fall slide
When considering mass wasting, which of the following factors is most influential in the downslope movement of weathered particles?
gravity
Which of the following is a reason the Gros Ventre rockslide took place?
Because the river eroded material at the valley base, there was no support of the material upslope.
Sphere
Biosphere Atmosphere Hydrosphere
Slide
Blocks of bedrock broken loose and sliding downhill
Part B - Slumps
Blocks of materials or unconsolidated sediments along a curved surface
Look at the image carefully. You will see several processes and features. Some of these are agents of mass wasting while others have resulted from the processes of mass wasting itself. Which of the following features is the result of mass wasting?
Boulders
Part B - Fall
Boulders on a rocky cliff
Which of the following external processes are clearly active/evident in the image above?
Erosion Mass wasting
How is a fall different from creep?
Falls occur rapidly and in areas with high slope, whereas creep occurs slowly in areas with low slope.
Part B - Flow
Fined-grained materials that can easily flow like a liquid
Event
A wildfire burns through a section of forest. Humans create a new highway road cut.
___________ are very gradual mass movements in which the whole slope moves downhill slowly.
Creeps
How are debris avalanches and flows related?
Debris avalanches are large, rapid flows of rock.
How is a lahar different from a debris flow that might occur in southern California?
Debris flows are composed of soil and regolith, whereas lahars are composed of volcanic materials.
What is the difference between an earthflow and a debris flow?
Debris flows generally occur within semiarid areas and tend to be restricted to channels, whereas earthflows most often occur on hillsides in humid areas.
Describe how a soil particle moves downhill during the freeze-thaw process.
During the freeze, a soil particle moves at a right angle away from the surface, and thawing causes the particle to fall back to a slightly lower lever.
What is the significance of the angle of repose in regard to mass wasting?
If a slope becomes any steeper than the angle of repose, then material will start moving downslope via mass wasting.
What is the relationship between earthquakes and landslides?
If a slope that has not previously experienced mass wasting is covered by surface materials that are saturated with water, the vibrations of an earthquake may trigger liquefaction of these materials, causing them to travel downslope. If a slope exists under conditions that favor mass wasting but has not had any movement occur, the shaking force from an earthquake may jar the material loose from the slope.
How does water affect mass movement processes?
Large amount of water fills the pores between sediment, destroying the sediment's overall cohesion. When few water is added to make the sediment on a slope slightly damp, the sediment sticks together and resists downward pull. Water adds weight to the material on a slope, making the slope to fall.
Define mass movement. How does it differ from erosional agents such as streams, glaciers, and wind?
Mass movement is the downslope movement of rock material driven by the force of gravity. It differs from erosional processes in that mass movement does not require a transporting medium.
Part B - Creep
Piece of rock and loose sediments gradually transported downhill; movement of such material is unseen
Process
Saturates surrounding soil with water and increases evaporation. Quickly and drastically loosens rock material on a steep slope. Removes material from below the ground surface, allowing for subsidence or collapse of the ground.
How are slumps and slides related?
Slumps are a type of slide in the special case where the rupture surface is curved.
____________is an example of mass wasting commonly seen in the active layer above permafrost.
Solifluction
During which season does solifluction occur in the Arctic, and why?
Solifluction occurs during the Arctic's summer, when the top meter or so of the active layer thaws. Because the resulting meltwater has nowhere to go, it saturates the active layer, causing it to slowly flow.
Which of the following correctly states the role of rivers and mass wasting in the formation of the Grand Canyon?
The Colorado River erodes downward, then mass-wasting processes move material from high to low areas, then the Colorado River transports material downstream.
Define mass wasting.
The downslope movement of sediment and rock under the direct influence of gravity.
If permafrost is melted, which of the following is a consequence?
The ground subsides because the volume of water is less than that of ice.
Which of the following statements is true regarding the aftermath of the Gros Ventre rockslide?
The rockslide debris dammed up the river and formed a lake.
What would likely happen to a fence on a hill over time if the fence were built perpendicular to the hill's slope?
The top of the fence would likely bend uphill as creeping rocks moved under the fence and pushed the fence bottom downslope.
Why would trees be J-shaped?
The trunks become tilted in the downhill direction due to creep, but continue to grow toward the sun.
Slump
Triggered by curved oversteepened slopes
Fall
Triggered by ice wedging or plant activities on steep slopes
Flow
Triggered by large amounts of water and steep slopes
Creep
Triggered by repeated freezing and thawing of soils on gentle slopes
Which of the following responses are examples of how water can promote mass wasting?
When water is added to weathered particles, the mass of the sediment is increased, which can cause slope instability. Water can saturate sediment, reducing the integrity of the slope and allowing it to move. Waves and streams can undercut banks and cliffs, causing them to fail.
A____________ is a common result of creep.
broken retaining wall
Over time, mass wasting causes _________.
canyons to widen
A______________ acted as a sliding surface across which material moved downhill during the Gros Ventre Slide.
clay layer
Creep is ____________.
mass wasting by the gradual downhill movement of sediment, influenced by freeze-thaw or wet-dry cycles.
What is mass movement?
movement of material under the influence of gravity alone
Permafrost is ___________.
permanently frozen ground of tundra and subarctic climates that has remained 0 degrees Celsius for two years or more
Heavy rainfall caused the clay to lubricate and the sandstone to become _______________.
saturated and heavy
What rock type is the easiest for a river to cut through?
shale
A mass movement in which a cohesive block of earth or rock slips downhill relatively quickly in one piece along a zone of weakness is called a ____________.
slide
A________________ is formed when vertical incision by a stream is the primary process, with relatively minimal mass wasting.
slot canyon
Which of the following is associated with creep?
slow and subtle movement of material
Mass movements that move blocks of materials and unconsolidated materials down a curved surface creating scarps on a slope are known as ___________.
slump
What is used to keep the Trans-Alaska pipeline from melting permafrost?
stilts
What is name of the near-surface layer that thaws in the summer?
the active layer
