Geology Chapter 15

Slide

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

Why can rock avalanches move at such great speeds?

Air becomes trapped and compressed beneath the falling mass of debris, which allows the debris to move as a flexible sheet across the surface of the slope.

What causes creep, and how can it be recognized?

Creep is caused by the repeated expansion and contraction of the regolith, which may be caused by repeated freezing and thawing or wetting and drying. Creep can be recognized by tilted trees, tilted fences, and displaced retaining walls.

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.

Forest Fire

Forest Fire alters soil: 'Bakes' the ground Can cause top layer to become dry and loose

Which of the following landslides was caused in part because the underlying sedimentary bedrock was oriented parallel to the slope that failed?

Gros Ventre Landslide (Wyoming)

Rapid movements

In the mountains, mechanical weathering produces angular rock fragments that fall to the base of a cliff. Over time, a talus slope forms.

Slump

Mass movements that move blocks of materials and unconsolidated materials down a curved surface creating scarps on a slope are known as

stream valleys

Mass wasting and running water produce ______.

What is mass wasting, and how does it differ from other erosional processes (e.g., streams, glaciers, wind)?

Mass wasting is the downslope movement of rock material driven by the force of gravity. It differs from other erosional processes in that mass wasting does not require a transporting medium.

Part complete What is permafrost, and what can result from disturbing it?

Permafrost is permanently frozen ground. If the thermal balance of permafrost is disturbed, ice within the permafrost may melt, causing the ground to slide, slump, or subside.

Mass Wasting Triggers

Saturation of materials with water Oversteepening of slopes Removal of anchoring vegetation Ground vibrations from earthquakes

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.

What landscape feature indicates that mass wasting has helped shaped a river valley?

The river valley is much wider than it is deep.

Classification of mass wasting based on:

Type of material involved: -debris, mud, earth, rock Kind of motion displayed: -fall, slide, flow Velocity of movement

How can the addition of water make a slope fail, creating a landslide?

Water can easily flow downslope. Water makes the slope material heavier. Water in pore spaces reduces cohesion between particles.

Fall

When large rocks become dislodged and drop down a steep slope, the mass movement is called a

Flow

When unconsolidated material moves downslope as a viscous fluid it is called a

____ is a trigger for mass wasting.

a wildfire oversteepening of a slope adding water to sediments

In which environment are rapid mass-wasting processes most likely to occur?

among rugged, geologically young mountains

Angle of Repose

angle at which a material assumes a stable slope Typically 25 to 40 degrees for unconsolidated granular particles

Creeps

are very gradual mass movements in which the whole slope moves downhill slowly.

Which of the following triggers generated the 1958 landslide and tsunami at Lituya Bay, Alaska?

earthquake

Which of the following is the major contributing factor in all landslides?

gravity

oversteepened slope

has a slope angle steeper than the angle of repose for that material

In a river valley, mass-wasting processes can ______.

make the valley walls less steep make the river valley wider

Which landscape is most prone to generating landslides?

mountains

Permafrost

permanently frozen ground near and in Earth's polar regions

What terms are used to describe the way material moves during mass wasting?

slide fall flow

Rapid mass-wasting events do not always need a trigger.

true