Unit 8

Question 1

Landslide

Answer 1

a sudden event where large quantities of rock and soil move down steep slopes

Question 2

Mass Wasting

Answer 2

the downslope movement of rock, regolith, and soil under the direct influence of gravity

Question 3

What process does Mass wasting normally follow?

Answer 3

Weathering

Question 4

What is the controlling force of mass wasting?

Answer 4

Gravity

Question 5

What does saturating sediment do?

Answer 5

Saturation reduces friction

Question 6

Angle of repose

Answer 6

The steepest angle at which a material can remain stable

Question 7

What are the controls and triggers of mass wasting

Answer 7

• Oversteepened Hills
• Removal of Vegetation
• Earthquakes
• Slope materials gradually weaken over time- eventually if the strength falls below what is necessary to maintain slope stability, a landslide will occur

Question 8

How can plants protect against erosion?

Answer 8

Plants protect against erosions by binding soil and regolith together.
They also shield the soil surface from raindrop impacts

Question 9

How is vegetation removed?

Answer 9

By humans or by forest fires

Question 10

How can earthquakes trigger mass wasting?

Answer 10

Earthquakes and aftershocks can dislodge rocks and unconsolidated materials

Question 11

Liquefaction

Answer 11

During periods of ground shaking, water-saturated surface materials behave as fluid-like masses that flow

Question 12

How are mass wasting processes classified?

Answer 12

By the type of material:

– Debris, mud, and earth are used if soil and regolith move

– “Rock” is used if bedrock moves

Question 13

Types of Motion in Mass wasting

Answer 13

• Fall
• Slide
• Flow

Question 14

Fall (Type of Motion)

Answer 14

The free fall of detached pieces

Question 15

Talus Slopes

Answer 15

Built by rock fall

Question 16

Slide (Type of Motion)

Answer 16

slide occurs when there is a distinct zone of weakness separating the slide material from the underlying material

Question 17

Rotational Slide

Answer 17

surface of rupture is concave up

Question 18

Translational Slide

Answer 18

material moves along a flat surface

Question 19

Flow (Type of Motion)

Answer 19

occurs when material moves downslope as a viscous fluid

Most are saturated with water

Question 20

What are the different rates of movement for classifying mass wasting processes?

Answer 20

• Fast

- slow

Question 21

Fast (Rate of Movement)

Answer 21

A rock avalanche is the most rapid type of mass wasting – Rocks float on air as they move downslope

Question 22

Slow (Rate of movement)

Answer 22

• Creep moves particles a few millimeters per year

- A wide range of rates exists between these two extremes

Question 23

What are the classifications for mass wasting processes?

Answer 23

• Type of Motion

- Rate of movement

Question 24

Rapid forms of mass wasting

Answer 24

• Slump
• Rockslide
• Debris Flow
• Lahar
• Earth Flow

Question 25

Slump

Answer 25

• Rapid form of mass wasting

– A slump is the movement of a mass of rock or unconsolidated material as a unit along a curved surface (rotational slide) (Can involve a single mass or multiple blocks)

– Occurs along oversteepened slopes

Question 26

Rockslide

Answer 26

• Rapid form of mass wasting

occurs when blocks of bedrock slide down a slope

• A debris slide occurs when unconsolidated material slides down a slope

– Generally very fast and destructive

– Sometimes triggered by melting snow or rain

• Most common during the spring

– Sometimes triggered by earthquakes
• New Madrid, Yellowstone, Gros Ventre

Question 27

Debris Flow

Answer 27

rapid form of mass wasting that involves the flow of soil and regolith with water (mudflow if the material is fine grained)

– Tend to occur more frequently in semi-arid mountainous regions

• Sudden rainfall or snowmelt washes large quantities of sediment into rivers

– Lack of vegetation to anchor soil

– Often confined to channels and canyons

Question 28

Lahar

Answer 28

Rapid form of Mass Wasting

Debris flows composed mostly of volcanic materials

• Example: Mount St. Helens

– Historically some of the most deadly volcanic hazards

• Can occur during a volcanic eruption or when a volcano is quiet
• Take place when highly unstable layers of ash and debris become saturated with water
• Generally follow stream channels

Question 29

Earthflow

Answer 29

Rapid form of mass wasting

Earthflows form on hillsides in humid regions during heavy precipitation or snowmelt

• Water saturates the soil and regolith
– Commonly involve materials rich in clay and silt

• Very viscous, move at slower rates than more fluid debris flows

– Range in size from a few meters to more than a kilometer long and several hundred meters wide!

Question 30

Slow forms of mass wasting

Answer 30

• Creeps
• solifluction
• The Sensitive Permafrost Landscape

Question 31

Creep

Answer 31

Creep is the gradual movement of soil and regolith downhill

• Imperceptibly slow!
• Aided by the alternate expansion and contraction of the surface material
• Caused by freezing and thawing or wetting and drying – Causes fences and utility walls to tilt

Question 32

Solifluction

Answer 32

the downslope movement of water logged soils

• Literally: “soil flow”
• Promoted by a deeper dense clay hardpan or impermeable bedrock layer
• Common in regions underlain by permafrost

– Occurs in the active layer, the zone above the permafros

Question 33

The Sensitive Permafrost Lanscape

Answer 33

Permafrost is permanently frozen ground

• Summers are too short and cool to melt ice below the
shallow surface

• Deeper ground remains below 0oC (32oF) throughout the year

– Extensive around the Arctic Ocean

• Land use is regulated to prevent the permafrost from melting