Lecture 12 Flashcards
What is the controlling force of mass wasting ?
Gravity
Why the trigger is not the sole ?
Because it is the last straw
What are others contributing factors of mass wasting ? (IMPORTANT)
- Saturation of material with water
- Over-steepened slopes : unstable
- Loss of anchoring vegetation
- Earthquake ground vibration
What is the role of water ? (IMPORTANT)
- Saturation of the material with water
- May occur from heavy rainfall or snowmelt
- Reduces particle cohesion and friction
- Water adds weight to the sediment and gravity pulls it downwards
What is mass wasting?
Downslope movement of rock, regolith, and soil under influence of gravity.
Not requiring a transporting medium like water, wind, or ice
How does mass wasting contribute to landform development?
Widens valleys by carrying debris downslope after weathering weakens rocks, working alongside running water to shape stream valleys.
What are the main controls and triggers of mass wasting
- Gravity: controlling force
- Triggers : water saturation, over-steepened slopes, loss of vegetation, and earthquakes.
How does water saturation affect slope stability?
Reduces particle cohesion, adds weight, and increases the downward pull of gravity, making slopes more prone to failure.
What is the angle of repose?
25º to 40º
What happens when slopes exceed the angle of repose?
- Unstable
- Sediments falls
What are the effects of removing vegetation on slopes?
- Increases erosion
- Slope instability
How do earthquakes trigger mass wasting?
Dislodge rocks and soil.
Water-saturated materials can liquefy = like fluid and flowing downhill.
What are the three types of motion in mass wasting?
- Fall: Particles drop through air = talus slopes.
- Slide: Material moves along surface as coherent mass.
- Flow: Material moves down as a viscous fluid.
What factors classify mass wasting processes?
- Material type: Soil/regolith (debris or earth) or bedrock (rock).
- Rate of movement: Sudden or gradual
What is a slump (rotational slide)?
A mass of material slides along a curved surface, creating a spoon-shaped scarp and tilting backward.
What is a debris flow?
A rapid flow of soil, regolith, and water, often in mountainous or volcanic regions, confined to canyons or channels.
What are some preventive measures to reduce or lessen the impact of mass wasting?
- Drain slopes using drainage tiles and drilled holes.
- Insert rock bolts (anchors) to secure rock faces.
- Cover faces with wire mesh or spray cement.
- Install retaining walls to keep debris off infrastructure.
- Plant vegetation with strong root systems.
- Prevent undercutting of slopes.
How does water affect the internal cohesion of clay-bearing soils and regolith?
The soil or regolith has less internal cohesion when wet than when dry.
What two properties of rainwater and snowmelt have the greatest effect on soil strength and slope stability?
Increased lubrication and added weight.
What is the major and immediate controlling force in mass wasting?
Gravity, as this pulls matter downhill.
How much of Alaska and Canada is covered by permafrost?
Permafrost covers over 80% of Alaska and about 50% of Canada.
What are periglacial features?
Pingoes: Ice-cored mounds above ponds or lakes.
Palsas: Peat mounds with ice lenses.
Felsenmeer: Bedrock shards covering the ground.
Thermokarst: Thaw lakes formed from melting permafrost.
What is solifluction?
A slow, saturated soil flow common in permafrost regions, where water cannot escape deeper layers, often forming lobes on gentle slopes.
What is creep?
The gradual downhill movement of soil and regolith, caused by freezing/thawing or wetting/drying cycles, leading to tilted fences and J-shaped trees.
