EOSC 114 LANDSLIDES Exam 2025
Questions with Correct Answers |New
Version with complete solutions
Mass Movement/Wasting - Answers -✔✔ Movement of earth material downslope due to
gravity.
Landslide - Answers -✔✔ Specific type of mass movement involving sliding.
Human Vulnerability to Landslides is Increasing Cause: - Answers -✔✔ Of population
growth in mountainous areas, and more infrastructure near unstable slopes.
Why Is BC Prone to Landslides? - Answers -✔✔ 1. Steep mountainous terrain
2. heavy rainfall
3. unconsolidated glacial sediments
4. complex geology
5. many natural and human triggers
Landslide Classification is Based On: - Answers -✔✔ 1. Material: Rock, soil, mud,
debris
2. Type of Movement: Fall, slide, flow, complex
3. Rate of Movement: Fast or slow
(Landslides) Falls - Answers -✔✔ A sudden detachment on steep slopes caused by
fractures or weakness that are VERY FAST.
(Landslides) Slides - Answers -✔✔ Cohesive movement along a failure surface: either;
1. Rotational (slump): curved surface, slower, weak materials
2. Translational: Flat surface, faster, stronger material
(Landslides) Flows - Answers -✔✔ Chaotic, fluid-like movement of debris, ranging from
slow to fast, water content is higher
(Landslide) Complex Movements - Answers -✔✔ Combination of the above (e.g a slide
becomes a flow)
(Landslides) Soil Creep - Answers -✔✔ Slowest movement, surface materials shift
subtly over time.
Shape of Failure Surface - Answers -✔✔ MOST important difference between landslide
types
,Angle of Repose - Answers -✔✔ Steepest angle a loose material can hold without
sliding, depends on: material type, particle size/shape, & moisture
content...Steeper=less stable. At angle of repose: Fs= ~1
Adding Water to Loose Material: - Answers -✔✔ can either stabilize (cohesion) or
destabilize (overload + lubrication)
Stability of Slopes: Driving Forces - Answers -✔✔ Gravity leads to shear stress
(τ)=downslope pulling force.
The steeper the slope the stronger the stress is.
Stability of Slopes: Resisting Forces - Answers -✔✔ 1. Friction (resists sliding)
2. Cohesion (how well materials stick together)
3. Combined=Shear Strength(τf)
Factor of Safety (Fs) - Answers -✔✔ Fs= Shear Strength(τf) divided by Shear Stress (τ)
....
Fs>1=stable
Fs=1=slope on edge
Fs<1=failure likely
Material Strength: Crystalline Rock - Answers -✔✔ Friction: Mod.
Cohesion: Very High
Avg. Strength: High
Material Strength: Sedimentary Rock - Answers -✔✔ Friction: Mod.
Cohesion: Mod-High
Avg. Strength: Mod.
Material Strength: Sediment - Answers -✔✔ Friction: Low-Mod.
Cohesion: Low
Avg. Strength: Low
Landslide CAUSE - Answers -✔✔ Long term weakening:
-lowers shear strength/raises stress
-doesn't directly initiate movement
Landslide TRIGGER - Answers -✔✔ Specific short-term event:
-initiates the landslide
-there can be many causes, but only one trigger e.g rainstorm, earthquake, etc. Failure
occurs when Fs drops to 1.0
External Causes: Slope Angle - Answers -✔✔ No slope= no landslide
Steeper= more potential movement
, External Causes: Undercutting - Answers -✔✔ Base of slope removed by rivers, roads,
waves, excavation, etc
External Causes: Overloading - Answers -✔✔ Added weight on top of slope
Can be buildings, fill, snow, etc.
External Causes: Vegetation - Answers -✔✔ Stabilizes the slope because:
1. roots bind the soil
2. removes water via transpiration
External Causes: Climate - Answers -✔✔ 1. More rain→more water=more mass + less
cohesion
2. Weathering weakens rock
3. Freeze-thaw cycles cracks and loosens rock
4. Atmospheric rivers=major external trigger (like BC storm)
Internal Causes of Landslides - Answers -✔✔ These are factors inside the slope that
reduce shear strength(τf) or shear stress(τ).
1. Water Content
2. Freeze-Thaw/Frost Wedging
3. Inherently Weak Materials
4. Adverse Geologic Structures
Internal Causes: Water Content - Answers -✔✔ Water on slopes:
-Adds weight, increasing driving force(τ).
-Reduces friction between particles, lowering resisting force(τf).
-Is a medium for flows
-Can cause saturation, mainly in sediments
-In solid rock, water infiltrates fractures & weakens the rock
Water Content Effect on Angle of Repose - Answers -✔✔ No water=low angle
Some water=higher angle (stability)
Too much water=very unstable, flows easily
Internal Causes: Freeze-Thaw/Frost Wedging - Answers -✔✔ Water in cracks expands
when frozen which widens fractures.
Weakens slope over time.
More rockfalls in colder alpine zones.
Internal Causes: Inherently Weak Materials - Answers -✔✔ Fail even at a low slope
angle.
example: -volcanic rock (weak layering, weathered ash)
-quick clay (special type of marine clay)
Questions with Correct Answers |New
Version with complete solutions
Mass Movement/Wasting - Answers -✔✔ Movement of earth material downslope due to
gravity.
Landslide - Answers -✔✔ Specific type of mass movement involving sliding.
Human Vulnerability to Landslides is Increasing Cause: - Answers -✔✔ Of population
growth in mountainous areas, and more infrastructure near unstable slopes.
Why Is BC Prone to Landslides? - Answers -✔✔ 1. Steep mountainous terrain
2. heavy rainfall
3. unconsolidated glacial sediments
4. complex geology
5. many natural and human triggers
Landslide Classification is Based On: - Answers -✔✔ 1. Material: Rock, soil, mud,
debris
2. Type of Movement: Fall, slide, flow, complex
3. Rate of Movement: Fast or slow
(Landslides) Falls - Answers -✔✔ A sudden detachment on steep slopes caused by
fractures or weakness that are VERY FAST.
(Landslides) Slides - Answers -✔✔ Cohesive movement along a failure surface: either;
1. Rotational (slump): curved surface, slower, weak materials
2. Translational: Flat surface, faster, stronger material
(Landslides) Flows - Answers -✔✔ Chaotic, fluid-like movement of debris, ranging from
slow to fast, water content is higher
(Landslide) Complex Movements - Answers -✔✔ Combination of the above (e.g a slide
becomes a flow)
(Landslides) Soil Creep - Answers -✔✔ Slowest movement, surface materials shift
subtly over time.
Shape of Failure Surface - Answers -✔✔ MOST important difference between landslide
types
,Angle of Repose - Answers -✔✔ Steepest angle a loose material can hold without
sliding, depends on: material type, particle size/shape, & moisture
content...Steeper=less stable. At angle of repose: Fs= ~1
Adding Water to Loose Material: - Answers -✔✔ can either stabilize (cohesion) or
destabilize (overload + lubrication)
Stability of Slopes: Driving Forces - Answers -✔✔ Gravity leads to shear stress
(τ)=downslope pulling force.
The steeper the slope the stronger the stress is.
Stability of Slopes: Resisting Forces - Answers -✔✔ 1. Friction (resists sliding)
2. Cohesion (how well materials stick together)
3. Combined=Shear Strength(τf)
Factor of Safety (Fs) - Answers -✔✔ Fs= Shear Strength(τf) divided by Shear Stress (τ)
....
Fs>1=stable
Fs=1=slope on edge
Fs<1=failure likely
Material Strength: Crystalline Rock - Answers -✔✔ Friction: Mod.
Cohesion: Very High
Avg. Strength: High
Material Strength: Sedimentary Rock - Answers -✔✔ Friction: Mod.
Cohesion: Mod-High
Avg. Strength: Mod.
Material Strength: Sediment - Answers -✔✔ Friction: Low-Mod.
Cohesion: Low
Avg. Strength: Low
Landslide CAUSE - Answers -✔✔ Long term weakening:
-lowers shear strength/raises stress
-doesn't directly initiate movement
Landslide TRIGGER - Answers -✔✔ Specific short-term event:
-initiates the landslide
-there can be many causes, but only one trigger e.g rainstorm, earthquake, etc. Failure
occurs when Fs drops to 1.0
External Causes: Slope Angle - Answers -✔✔ No slope= no landslide
Steeper= more potential movement
, External Causes: Undercutting - Answers -✔✔ Base of slope removed by rivers, roads,
waves, excavation, etc
External Causes: Overloading - Answers -✔✔ Added weight on top of slope
Can be buildings, fill, snow, etc.
External Causes: Vegetation - Answers -✔✔ Stabilizes the slope because:
1. roots bind the soil
2. removes water via transpiration
External Causes: Climate - Answers -✔✔ 1. More rain→more water=more mass + less
cohesion
2. Weathering weakens rock
3. Freeze-thaw cycles cracks and loosens rock
4. Atmospheric rivers=major external trigger (like BC storm)
Internal Causes of Landslides - Answers -✔✔ These are factors inside the slope that
reduce shear strength(τf) or shear stress(τ).
1. Water Content
2. Freeze-Thaw/Frost Wedging
3. Inherently Weak Materials
4. Adverse Geologic Structures
Internal Causes: Water Content - Answers -✔✔ Water on slopes:
-Adds weight, increasing driving force(τ).
-Reduces friction between particles, lowering resisting force(τf).
-Is a medium for flows
-Can cause saturation, mainly in sediments
-In solid rock, water infiltrates fractures & weakens the rock
Water Content Effect on Angle of Repose - Answers -✔✔ No water=low angle
Some water=higher angle (stability)
Too much water=very unstable, flows easily
Internal Causes: Freeze-Thaw/Frost Wedging - Answers -✔✔ Water in cracks expands
when frozen which widens fractures.
Weakens slope over time.
More rockfalls in colder alpine zones.
Internal Causes: Inherently Weak Materials - Answers -✔✔ Fail even at a low slope
angle.
example: -volcanic rock (weak layering, weathered ash)
-quick clay (special type of marine clay)
