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Lecture 15

GEG 1301 Lecture Notes - Lecture 15: Frost Heaving, Permafrost, Solifluction

Course Code
GEG 1301
Denis Lacelle

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Slope Processes
December 2, 2015
- Slope processes are primarily controlled by gravity
Water and ice may play a role, but they are not dominant
- While creep is typically a slow process, it can be quite rapid under the right conditions
Freeze-thaw movement = Discontinuous creep
- Continuous creep is caused by the deformation of the soil/rock due to its own weight
Typically less than 1 mm per year
Can be faster in permafrost environments (rock glaciers – several cm/year)
- Solifluction: A combination of frost creep and gelifluction (downslope movement of
saturated soil), leads to internal deformation
Surface rates ~ 1-5 cm/year, as you get deeper speed decreases
- One-sided freezing = concave downslope velocity profile, seasonally
frozen ground and discontinuous permafrost
- Two-sided freezing = convex downslope velocity profile, continuous
Can form lobes or sheets (from a few m – 10s of m, and rising 0.5-3 m)
No upslope scar zone
- Flows: Movement incorporating viscous, fluid or plastic motion (high moisture content),
typically leaves scars
Earthflow: Slowest flow, rarely cause damage, crescent scar, short flow track and
bulging lobe. Vegetation tends to remain intact
Mudflow: Most fluid & fastest flow, most dangerous. At least 50% fine material
& >30% water. Basin-shaped source, long narrow track and expanded deposition
Debris flow: Similar form to mudflows (deposition is more spread out), but
contain large particles and are usually slower. Most often caused by heavy
Quick clay flow: Horse-shoe shaped with slumping around the headwall &
mudflows on the floors. Caused by the leeching out of marine salts from Leda
clays. Clay is liquefied & flows due to high precipitation or an earthquake
- End of material for the final
- Slides:
Slumps: Movement of cohesive mass of sediments, failure surface is deep-seated
and curved
Rock slide:
Debris slide:
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