Geology Chapter 8

Which statement best describes slumping, a mass wasting process?

a block or blocks of unconsolidated regolith slide downhill along a curved slip surface

How do the strength and cohesion of clay-rich regolith or soil change with the addition of water?

water lowers the strength and cohesion

The steepest, stable, slope angle possible in unconsolidated, granular materials like sand and gravel is called the angle of retention.

false

Consider a steep highway cut made by removing slightly weathered to fresh, fractured, granite bedrock. Which of the following situations is most stable against rockslides?

one set of widely spaced, sub-horizontal fractures

A scarp is the exposed portion of the rupture surface beneath a slump block.

true

What caused the mudflows (1985) on the Nevado del Ruiz volcano?

hot ash fell onto snow near the summit

Consider a weathered rock or soil particle lying on a slope. How will the gravitational force pulling the particle downward along the land surface vary with the inclination of the slope?

it will decrease as the slope angle is lessened

During wet weather or times when snow is melting, sometimes the downhill toe of a slump ________.

becomes an earth flow

Slump describes the very slow, downhill movement of soil and regolith.

false

How do freezing, thawing, wetting, and drying contribute to soil creep?

the soil expands and contracts, lifting particles and dropping them a slight distance downslope

All of the following are possible indicators that creep is occurring except for ________.

an extremely thick soil profile

A geologist wants to locate a horizontal coal bed on a soil-covered slope where soil creep is active. A distinctive sandstone bed underlies the coal bed. On the basis of weathered sandstone fragments in the soil, where is the coal bed?

just above the highest piece of sandstone seen in the soil

Which of the following was a major factor leading to the Gros Ventre, WY slide?

soils and shallow bedrock were very wet and locally saturated

Which disaster was triggered by a huge mass of soil and rock that suddenly slid into a water-filled reservoir?

Vaiont Canyon, Italy, 1963

Of the following, which one would most likely be triggered by an earthquake?

rock avalanche

Which mass wasting process has the slowest rate of movement?

creep

The Gros Ventre slide of 1925 was actually a mudflow triggered by an earthquake.

false

A triggering mechanism, such as heavy rains or an earthquake, are necessary for mass wasting to occur.

false

Lahars are essentially mudflows associated with volcanoes and volcanism.

true

Which one of the following operates primarily in areas of permafrost?

solifluction

________ denotes the exposed, crescent-shaped rupture surface at the head of a slump.

scarp

Earthflows and slumps generally involve movement of unconsolidated or weakly consolidated soil and regolith.

true

Bedding planes and fractures can both act as slip surfaces for rockslides.

true

Which one of the following materials has the maximum, sustainable, slope angle, as determined by the angle of repose?

dry sand

The most rapid type of mass movement is a ________.

rock avalanche

Repeated freezing and thawing can be important in soil creep movements.

true

All of the following are factors affecting mass wasting except for ________.

geologic age

Submarine landslides are generally much smaller than similar mass wasting events on land.

false

Solifluction is an important mass wasting process in areas of permafrost.

true

Solifluction occurs during the warmer summer months.

true