Introduction to Mass Wasting Effects

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Questions and Answers

What is the primary driving force behind mass wasting?

Human activities

Magnetic forces

Wind erosion

Gravity (correct)

Which of the following factors does NOT influence the rate of mass wasting?

Vegetation

Slope

Soil color (correct)

Water or Ice

When the shear strength is greater than the shear force, what is the outcome?

Debris will disintegrate

Debris will remain in place (correct)

Debris will flow easily

Debris will erode quickly

What effect does water saturation have on debris during mass wasting?

Increases likelihood of flowing Signup and view all the answers

Which is considered a trigger of mass wasting?

Heavy rainfall Signup and view all the answers

How does vegetation influence mass wasting?

Provides stability through root systems Signup and view all the answers

Which force attempts to hold rock in place against mass wasting?

Normal force Signup and view all the answers

What effect does increased pore pressure from water have during mass wasting?

Decreases shear strength Signup and view all the answers

What is the classification of mass wasting based on the rate of movement?

Less than 1 cm/year Signup and view all the answers

Which type of material is classified as 'debris' in mass wasting?

Unconsolidated material at Earth's surface Signup and view all the answers

What distinguishes a translational slide from a rotational slide?

Translational slides move along a plane parallel to the slope. Signup and view all the answers

What is 'creep' in the context of mass wasting?

Very slow downward movement of soil or unconsolidated debris. Signup and view all the answers

What characterizes a slump in mass wasting?

Material moves en masse along a curved surface. Signup and view all the answers

Which of the following is NOT a type of flow in mass wasting?

Glacial flow Signup and view all the answers

What triggers an earthflow?

Heavy rain saturating soil Signup and view all the answers

What happens during a debris flow?

Motion occurs with soil, regolith, and large amounts of water. Signup and view all the answers

What is solifluction primarily associated with?

Colder climates Signup and view all the answers

What material typically underlies saturated soil in solifluction?

Bedrock or permafrost Signup and view all the answers

What type of flow is characterized by a mixture of debris and water, generally occurring through a channel?

Mud flow Signup and view all the answers

Which type of mass wasting event is the fastest and most turbulent?

Debris avalanche Signup and view all the answers

During a rockslide, which surface does the mass of bedrock typically slip along?

Inclined surface of weakness Signup and view all the answers

Which human activity can increase the risk of mass wasting?

Construction on slopes Signup and view all the answers

What kind of preventative measure can help reduce the risk of rockfalls and rockslides on highways?

Identifying planes of weakness Signup and view all the answers

What is one suggested measure to prevent mass wasting in debris?

Building terraces Signup and view all the answers

Study Notes

Mass Wasting Definition

Movement of bedrock, rock debris, or soil down a slope due to gravity.
Ranges from slow creep to fast landslides.

Mass Wasting Importance

Causes loss of life and property.
According to the USGS, mass wasting killed more people in the last 3 months of 1985 than other geologic hazards over 20 years.
Costs an average of $1.5 billion in the US and 25 lives per year.
Costs more than triple the combined cost of floods, earthquakes, hurricanes, and tornadoes.

Factors Influencing Mass Wasting

Slope: steeper slopes increase shear force.
Relief: the vertical distance between the valley floor and mountain summit.
Water or Ice: saturation increases weight and reduces shear strength.
Abundance of loose material: more material available for movement.
Vegetation: roots provide stability and anchor soil.
Earthquakes: seismic activity can trigger mass wasting.

Other Factors Influencing Mass Wasting

Orientation of weakness planes: bedding, foliation planes.
Climatic factors:
- Precipitation: heavy rainfall increases water saturation.
- Freezing and thawing: cycles can contribute to soil instability.

Gravity and Mass Wasting

The primary driving force in mass wasting.
Two forces involved:
- Normal force: perpendicular to the slope and holds rock in place.
- Shear force: parallel to the slope and causes movement.
Steeper slopes and heavier rocks increase shear force.

Shear Strength

Resistance to movement and deformation.
Controlled by the cohesiveness of the material and related to the normal force.
If shear strength is greater than shear force, debris will not move.

Water and Mass Wasting

A critical factor.
Water saturation makes debris heavier and more prone to flowing down.
Reduces shear strength by increasing pore pressure and forcing grains apart.

Mass Wasting Triggers

Seismic activity (earthquakes).
Heavy rainfall.
Construction: added weight and removal of vegetation.

Mass Wasting Classification

Based on:
- Rate of movement: slow to fast.
- Type of material: bedrock or debris.
- Nature of movement: flow, fall, slide.

Rate of Movement Classification

Ranges from less than 1 cm/year to over 100 km/hour.

Type of Material Classification

Debris: unconsolidated material at the Earth's surface, such as soil, rock fragments, earth, or mud.

Type of Movement Classification

Flow: descending downslope as a viscous fluid.
Fall: mass free-falls or bounces down a cliff.
Slide: descending mass remains relatively intact.

Types of Slides

Translational slide: mass moves along a plane parallel to the slope.
Rotational slide (slump): involves a curved surface. The upper part moves downward, while the lower part moves outward.

Types of Mass Wasting

Creep: very slow downward movement of soil or unconsolidated debris.
- Shear force is only slightly greater than shear strength.
- Rate: less than 1 cm per year.
- Factors: water and daily cycles of freezing and thawing.
- Plant roots help anchor the soil.
Slump: material moves en masse along a curved surface.
- Involves rotational slide.
- Usually does not travel fast or far.

Mass Wasting Flows

Earthflow: debris moves downward as a viscous fluid.
- Can occur slowly or rapidly.
- Usually occurs on hillsides with thick debris cover after heavy rains saturate the soil.
Solifluction: type of earthflow associated with colder climates.
- Flow of water-saturated debris over impermeable material like bedrock or permafrost.
Mudflow: flowing mixture of debris (fine-grained) and water, usually through a channel.
- Solid particles are normally clay or silt.
- Occurs after heavy rains.
- Common in areas without vegetative cover.
Debris avalanche: fastest variety of debris flow, turbulent mass of debris, air, and water.
Lahars: volcanic mudflows and debris.

Rockfall and Rockslides

Rockfall: bedrock breaks off and falls freely or bounces down a cliff. Talus forms at the base.
Rockslide: rapid slipping of bedrock along an inclined surface of weakness (bedding plane, fracture, foliation plane).

Debris Slides and Falls

Debris slide: coherent form of debris moving along a well-defined surface.
Debris fall: free-fall mass of debris.

Human Impact on Mass Wasting

Construction makes slopes susceptible to mass wasting:
- Undercutting slopes removes natural support.
- Removal of vegetation increases erosion and water in debris, increasing weight.
- Building on upper slopes also increases weight.

Preventing Mass Wasting in Debris

Building retaining walls where cuts have been made to a slope.
Installing drainpipes to remove water from debris.
Avoiding oversteepening of slopes by cutting back using terraces.

Preventing Rockfalls and Rockslides on Highways

Planes of weakness parallel to the slope of hills can lead to rockslides when road cuts are made.

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Description

Explore the critical concepts of mass wasting, including its definition, factors influencing it, and its significant impact on life and property. This quiz highlights how various elements such as slope, vegetation, and water can affect the likelihood of mass wasting events. Test your knowledge about this important geological hazard.