Mass Wasting and Slope Dynamics

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Questions and Answers

Which of the following best describes mass wasting?

The horizontal movement of soil due to wind.

The downslope movement of rock or soil as a coherent mass. (correct)

The upward movement of water in soil.

The lateral movement of tectonic plates.

Water saturation can act as a driving force in mass wasting.

True

What is the Angle of Repose?

The maximum slope angle at which a given unconsolidated material is stable.

The ____ factor is the ratio of resisting forces to driving forces in mass wasting.

Safety Signup and view all the answers

What type of mass wasting involves the rapid slide of rock along planes of weakness?

Rockslide Signup and view all the answers

Match the type of mass movement with its description:

Fall = Freefalling of detached individual pieces of any size. Slump = Downward slipping along a curved surface. Creep = Slow downhill movement of soil and regolith. Rock avalanche = Very rapid downslope movement of rock and debris. Signup and view all the answers

Deep-rooted vegetation can enhance mass wasting.

False Signup and view all the answers

What is a potential slip plane in the context of mass wasting?

Geologic surfaces of weakness such as bedding, foliation, or fractures. Signup and view all the answers

What percentage of particles in a debris flow are coarser than sand?

<blockquote> 50% </blockquote> Signup and view all the answers

Vegetation increases slope stability by completely removing the risk of landslides.

False Signup and view all the answers

List one factor that triggers rapid mass wasting.

Rain Signup and view all the answers

A __________ is the slow-moving flow of saturated materials during wet weather conditions.

mudflow Signup and view all the answers

Match the mass wasting processes with their characteristics:

Debris Flow = Flow of coarse material Rockslide = Movement on a low-friction surface Creep = Very slow movement Earthflow = Viscous debris flow Signup and view all the answers

Which of the following is NOT a measure to prevent landslides?

Increase load on the slope Signup and view all the answers

What role does water play in slope stability?

Water can saturate soil, leading to shallow slips and erosion, which decreases slope stability. Signup and view all the answers

Earthquakes are a factor that can trigger rapid mass wasting.

True Signup and view all the answers

Study Notes

Mass Wasting

Downslope movement of rock or soil
All inclusive term for any downslope movement of earth materials

Forces on Slopes

Driving forces: move earth materials downslope
- Downslope component of weight of material, including vegetation, fill material, or buildings
Resisting forces: oppose movement
- Strength of material

Potential Slip Planes

Surfaces of weakness in the slope material including bedding, foliation, and fractures

Angle of Repose

Maximum slope angle at which unconsolidated material is stable

Safety Factor

Ratio of resisting forces to driving forces (RF/DF)
- SF > 1: Slope is stable
- SF < 1: Slope is unstable

Triggers for Mass Wasting

Gravity: Driving force of all mass wasting
Undercutting: Stream eroding valley wall
Wave Action: Waves eroding base of cliffs

Role of Vegetation

Stabilizes ground through deep roots
Protects soil from erosional effects of rain
Mass wasting enhanced where plants are lacking: steep slopes, forest fires, human removal of plants.

Types of Mass Wasting

Fall: Freefalling of detached pieces of any size
Rockslide: Rapid slide of rock downslope along planes of weakness
Slump: Downward slipping of rock or unconsolidated material along a curved surface
Creep: Slow downhill movement of soil and regolith
Rock Avalanche: Very rapid downslope movement of rock and debris, can reach speeds of over 200 kilometers per hour
Debris Flow: Downslope flow of relatively coarse material, more than 50% of particles are coarser than sand

Debris Flow

Movement may be very slow or very fast
Mudflows, debris avalanches, and debris flows
- Small to moderate magnitude events
- Occasional large magnitude events

Earthflow

Viscous (thick) debris flow
Slow-moving
- Faster in wetter weather

Creep

Very slow movement
Result of freezing and thawing

Triggers for Rapid Mass Wasting

Rain: Triggers landslides and mass wasting
Oversteepening: Cutting at the foot of the slope or adding material at the head of the slope
Deforesting/Devegetating: Removal of vegetation
Earthquakes: Trigger landslides and mass wasting

Preventative Measures

Slope Reduction: Reduce slope angle, add supporting material, reduce the load
Retention Structure: Use ground covers or vegetation to prevent mass wasting
Fluid Removal: Decrease water content or pore pressure by improving drainage on slope surface

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Description

This quiz explores the concepts of mass wasting, the forces acting on slopes, and various factors influencing slope stability. It covers the mechanics involved, such as driving and resisting forces, as well as the importance of vegetation in preventing erosion.