Lecture 12: Periglacial Hazards: Highland and Lowland Flashcards
Amazing behaviour of ice/water/vapour:
Hard Strong Bonds Weak Mobile 9% Expansion
Permafrost is a physical state…
Ground that has been frozen for more than 2
consecutive winters
Main areas in permafrost
Active layer and Permafrost, plus unfrozen areas called talik
Main types of permafrost are…
Continuous (90-100% frozen), discontinuous (50-
90% frozen) and sporadic (10-50% frozen)… plus isolated (0-10% frozen)
Most common alpine, cold-climate hazard =
Snow avalanches
Speed of snow avalanches
- Hard to measure
* Related to amount of vertical fall and wetness of snow
Main types of avalanche:
- Loose snow
2. Slab-avalanche
Main controls of snow avalanches:
- Meteorology
2. Terrain
Main controls of snow avalanches:
1. Meteorology:
- Snow
- What happens after fall
- Particular weather patterns
Main controls of snow avalanches:
2. Terrain
• Slope angle 15o to 60o (especially 25o
to 40o)
• Aspect
• Roughness (trees)
Impact pressure (kPa) 1 5 30 100 1000
Potential damage Break windows Push in doors Destroy wood-framed structures Uproot mature spruce trees Move reinforced concrete structures
Permanent snow supporting
structures
Snow bridges and snow nets
Stone walls
Lowland periglacial permafrost hazards
Key factors
- Low altitude
- Frequently on large floodplains
- Areas of relatively high population
Lowland permafrost especially susceptible to thermokarst as it is:
- relatively warm
- frost susceptible (floodplain deposits)
- most populated and disturbed by human activity
Mitigation of lowland periglacial hazards
Management includes:
- Hazard mapping
- Geotechnical engineering
• Thermosyphons
• Piling
• Insulation
