Midterm Study Guide 6

Question 1

List three effects of water (e.g. via heavy rain) on mass wasting processes.

Answer 1

1) Water in permeable materials adds weight (mass)
2) Abundant water added to unconsolidated materials reduces their cohesiveness
3) Fluid pressures in earth materials reduces all normal stresses in those materials by the amount of the fluid pressure (the effective stress concept). Shear stresses are not affected.

Question 2

What range of velocities are spanned by mass wasting processes in nature?

Answer 2

Creep (mm to cm/yr) to catastrophic (several hundred km/hr).

Question 3

What is a toe and a head in the context of mass wasting?

Answer 3

toe = material pushed out at the base of the landslide; supports the landslide. Head = top of landslide that used to be part of the original ground surface.

Question 4

List three effects determining the likelihood of a landslide.

Answer 4

water content, friction, pressure

Question 5

What is anisotropy of strength?

Answer 5

When a certain material is stronger in a way rather than a different way

Question 6

What role does friction play in the stability of a hill side?

Answer 6

Friction holds everything in place. It helps keep all the grains or sediment more intact. The less friction the more it is deemed to fail.

Question 7

What is effective normal stress?

Answer 7

a force that keeps a collection of particles rigid. It normally applies to sand, soil or gravel. Example: If you pinch a stack of coins between your fingers, the stack stays together. If you then loosen the pressure between your fingers, the coin stack falls apart. Similarly, a pile of sand keeps from spreading out like a liquid because the weight of the sand keeps the grains stuck together in their current arrangement, mostly out of static friction. This weight and pressure is the effective stress

Question 8

What is the relationship between force and stress?

Answer 8

Stress = Force/Area

Depending on what you are holding constant stress is the outcome of greater force or greater area

Question 9

What role does erosion play in mass wasting?

Answer 9

shaping the landscape

Question 10

What is the angle of repose?

Answer 10

• The angle of repose is the steepest angle at
  which a pile of unconsolidated grains remains
  stable, and is controlled by the frictional
  contact between the grains. In general, for dry
  materials the angle of repose increases with
  increasing grain size.

Question 11

What man-made or natural processes can affect the stability of an existing hill side negatively?

Answer 11

Cutting into the hillside to form a flat surface for houses or roads - creates a very steep vertical cliff that is highly unstable.

Question 12

landslide

Answer 12

Landslide is any perceptible downslope movement of bedrock, regolith.

Question 13

friction coefficient

Answer 13

Friction coefficient is the ratio of the frictional force to the force acting perpendicular to the two surfaces in contact

Question 14

potential energy

Answer 14

the energy of an object or a system due to the position of the body or the arrangement of the particles of the system.

Question 15

erosion

Answer 15

Erosion is the process by which soil and rock are removed from the Earth’s surface by exogenetic processes such as wind or water flow, and then transported and deposited in other locations.

Question 16

effective normal stress

Answer 16

the force that keeps a collection of particles together.

Question 17

critical angle

Answer 17

Critical angle refers to the highest angle the light can possibly refract into or between objects without disappearing

Question 18

normal stress

Answer 18

Normal stress is the component perpendicular to each plane. Wants to hold rock together.

Question 19

rock fall

Answer 19

ice wedging often breaks rocks along joints, preparing them to loosen and fall away

Question 20

talus

Answer 20

Talus is a sloping mass of rock fragments at the foot of a cliff.

Question 21

fluid pressure

Answer 21

Fluid pressure is the pressure at some point within a fluid, such as water or air. reduces the normal stresses but doesn’t affect shear stresses. Once normal stress is gone, it’s more likely that things will slide.

Question 22

angle of repose

Answer 22

Angle of repose is the steepest angle at which a sloping surface formed of a particular loose material is stable.

Question 23

shear stress

Answer 23

Shear stress is defined as a stress which is applied parallel or tangential to a face of a material, as opposed to a normal stress which is applied perpendicularly. Wants to break rock apart.

Question 24

creep

Answer 24

a. Creep is the gradual downward movement of
disintegrated rock or soil due to gravitational
forces.

b. Two types of creep
i. Seasonal creep: movement of soil by heave
caused by expansion and contraction of soil,
wetting and drying , freeze thaw from
weather change (operates in upper few feet
of soil
ii. Continuous creep: strain reponse to stress
generated by weight of overburden driven
by gravity alone, not heave which may
affect consolidated rock ( function at levels
well below the surface)

*(hopefully this helps clarify the difference between all the slides, flows, etc.)

Question 25

Avalanche (flow)

Answer 25

flows downhill after eq loosens large masses – flows down on air (which acts as the fluid).

Question 26

Fall

Answer 26

rocks broken along joints and they free fall as individual blocks (rock fall). A vertical drop.

Question 27

Slide

Answer 27

• jointed bedrock layers broken along joints and
  move downhill as a unit (rock slide).
  • Slump – a mass slides down as a unit for a
    short distance fastly then stops,
    leads to a scar.
    - Debris soil – rock/soil/surface features like
    trees move as units downward. Key
    to slide – moving as unit.

Question 28

Flow

Answer 28

• Rain soaked stuff flows. Soil (earth flow) or a
  mixture of rock/mud/debris (debris flow).

       - Lahar – water and lava.