Landslides Flashcards
Landslide:
The movement of rock, earth, or debris down a slope due to gravity.
Mass Movement:
The downslope movement of rock, soil, and debris under the influence of gravity.
Slope Stability:
The resistance of a slope to failure or collapse.
Safety Factor:
A measure of slope stability that compares the forces resisting movement to the forces driving movement.
Types of Landslides:
Different classifications of landslides based on their movement characteristics, such as falls, slides, and flows.
Oso Landslide Event:
A specific landslide event that occurred in Washington State in 2014, known for its devastating impact.
Debris Flow:
A type of landslide characterized by the rapid movement of a mixture of rock, soil, and water down a slope.
What factors influence the speed of flows?
The speed of flows depends on the water content, type of materials, and the nature of the movement.
What causes creep?
Creep occurs due to the swelling and shrinking of the uppermost layer of the Earth’s surface.
What are mudflows?
Mudflows are fast-moving flows of mud, debris, and water.
What are lahars?
Lahars are volcanic mudflows, often triggered by volcanic eruptions.
What is the Bingham Canyon Mine known for?
The Bingham Canyon Mine is the largest open-pit copper mine in the United States.
What methods can be used to prevent mass movement?
Methods to prevent mass movement include building retaining walls, using rock bolts, controlling water, terracing, covering steep slopes, and reducing slope materials.
What is the purpose of retaining walls?
Retaining walls are built to hold back earth and prevent it from sliding or eroding.
What are rock bolts?
Rock bolts are long, anchored rods used to stabilize rock structures and prevent rockfall.
What is terracing?
Terracing involves creating steps on steep slopes to reduce the slope gradient and prevent erosion.
What are protective structures?
Protective structures are designed to shield areas from potential hazards, such as landslides or floods, by redirecting or containing the flow of materials.
Why is mass movement considered a costly type of natural hazard?
Mass movements can cause damage to living things and buildings, resulting in catastrophic losses.
How is the Safety Factor (SF) calculated to evaluate slope stability?
SF = Resisting forces / Driving forces. A SF > 1 indicates a safe or stable slope, while SF < 1 indicates an unsafe or unstable slope.
How does water affect slope stability?
Water can both increase and decrease slope strength. Small amounts increase surface tension between grains, while large amounts lubricate the grains, allowing them to flow more easily.
Why are slope failures common after forest fires?
Vegetation stabilizes slopes by slowing the removal of excess water and providing an effective stapling mechanism through roots. Removing vegetation can greatly increase the risk of slope failure.
How can earthquakes trigger mass movements?
Ground vibrations from earthquakes can decrease material friction and cause saturated sediments to liquefy, leading to mass movements.
What are the different types of flows in mass movement?
Flows include creep (slow), mudflow, debris flow, lahar (fast), and avalanche (very fast).
What is the angle of repose for fine sand?
The angle of repose for fine sand is approximately 35°.
What is the angle of repose for coarse sand?
The angle of repose for coarse sand is approximately 40°.
What is the angle of repose for angular pebbles?
The angle of repose for angular pebbles is approximately 45°.
What is the 1964 Great Alaska Earthquake known for?
The 1964 Great Alaska Earthquake triggered mass movements due to ground vibrations, causing decreased material friction and liquefaction of saturated sediments.
What are the primary factors for classifying types of mass movement?
The primary factors are the type of material, velocity of movement, amount of water present, and the type of movement (e.g., falls/slides, flows).
What are some examples of protective structures to prevent mass movements?
Protective structures include retaining walls designed to divert material, debris traps to prevent large debris movement, and shelters to minimize damage in areas prone to mass wasting.
What is subsidence?
Subsidence is the sinking of the land surface resulting from the removal of subsurface support, which can occur due to withdrawal of fluids, sinkholes, underground mining, and shrinking/swelling of clays.
What caused the 1963 Vaiont Dam disaster?
The 1963 Vaiont Dam disaster was caused by a landslide of 600 million tons of limestone into the reservoir, resulting in a destructive wave that destroyed villages and killed 2,600 people.
What was significant about the Bingham Canyon Mine Slide in 2013?
The Bingham Canyon Mine Slide in 2013 was the largest non-volcanic landslide in the known history of North America, causing substantial losses and halting production until the end of 2016.
Unconsolidated
granular material assumes a slope angle
angle of repose
The maximum angle at which a slope of loose materials will lie
without falling down
Angle of repose is a material property due to:
Particle size, shape, and the surface roughness
Which material (fine sand or angular pebbles) has the highest angle
of repose?
Angular Pebbles: 45°
Does adding water to dry sediments (i.e. sand) increase or decrease the
strength of the materials? Why?
Both!
depends on the amount of water
* Small amounts of water increase surface tension between grains
* Large amounts of water lubricate the grains, allowing them to
flow much more easily
Water reduces slope strength in several ways:
Water adds a lot of weight to the soil making it heavier
Water in the gaps between soil particles pushes them apart, making the soil break apart more easily
Water acts as lubricants between soil particles making them slide past each other more easily
true or false: Vegetation stabilizes slopes
True
True or false: earthquake can’t trigger mass movement
False, Earthquake can trigger mass movement
Four Primary Factors upon the classification type of mass movement:
- The type of material (rock,
regolith, snow, or ice) * Consolidated vs.
Unconsolidated - The velocity of movement
(fast, intermediate, or slow) - Amount of water present
- The type of movement
* Falls/Slides: moves more
or less as a coherent unit
* Flows: moves as if it were a
fluid
What does “Terra Firma” refer to?
Solid Earth.
What is a common characteristic of Earth’s surface?
It’s dynamic and not stable.
What triggers mass movements?
Changes in slope strength, water, and earthquakes
What happens to slope strength with water?
Water reduces the strength of the slope.
What can trigger mass movements after natural disasters?
Earthquakes and forest fires.
Describe the classification of mass movement.
It involves the rapid downhill movement of rock, debris, or soil from a steeply sloping surface by fall, bouncing, or rolling
How is talus formed?
It is formed by the accumulation of rock fragments due to weathering and mass movement.
True or false: is falls the fastest of all Rock movements?
True
What is shearing?
It’s when two big chunks slide past each other along a flat surface.
What happens in a slump?
The sliding surface is curved, and it’s a slow movement.
What is a debris or rock slide?
It’s when the sliding surface is flat, and it’s a faster movement.
Flows
Downslope movement of continuously internally deforming (mixing) materials
The type of flow is depended on?
Materials, water content and velocity
Minimizing the landslides hazard
1-evaluation of topography
2-types and conditions of bedrock that underlie slope
3-type and thickness of soil present
Subsidence can occur from
1-Withdrawal of fluids
2-sinkholes
3-underground mining
4- clays (shrinking/ swelling)
