Permafrost Flashcards
What is a permafrost?
- An area where material is frozen all year round.
- This area is not covered by snow or ice and so is exposed to fluctuations in air temperatures.
What is the active layer of permafrost?
- The active layer can be found at the top of the permafrost layer and alternates between thawing out through the summer and freezing in the winter, causing many problems for geotechnical engineers.
- Global warming is causing the active layer to increase in size, so materials which have been frozen for a long time are thawing out.
- These materials contain lots of methane which is released into the atmosphere which will cause a flip in the global climate.
What is found below a permafrost?
Frost-free soil, as it is closer to the hot core.
Where can permafrost be found?
- How deeply a permafrost reaches depends on how low the temperatures get at ground surface.
- Water insulated the ground below it and so you are less likely to find permafrost.
What are the different types of permafrost?
Why can permafrost areas be dangerous to build in?
- Areas where we have permafrost are very dry and so there is lots of transportation/deposition of sand and silt.
- This can easily fill hollows and gaps which can then be mistaken for solid ground.
Why is cryoturbation dangerous?
- When there is repeated freezing and thawing, the layers of deposition get mixed up in a process called cryoturbation because as the ground freezes it expands.
- This causes water to be drawn towards the freezing front.
- If the water moves through the ground quickly enough, thick lenses of ice form in the ground leading to lots of disruption/expansion.
How are ice-wedge casts formed?
- The ground freezes and shrinks resulting in cracks forming.
- This then fill with dust which is locked in place forming an ice-wedge cast.
How are stone polygon patterns formed?
Stones are moved around on the ground surface due to freezing and thawing depending on their size, leading to a pattern of stone polygons.
How are pingos formed?
- The ground around a lake freezes which traps the water inside the lake.
- Then, as the ground below the lake begins to freeze, the ice can only be forced upwards increasing pressure.
- This freezing draws water towards it producing thick lenses of ice which force the soil upwards to form mounds which eventually crack.
- These mounds are found in lakes and made up of blocks of ice covered in deposited sediment.
How are open system pingos formed?
Open system pingos are formed on spring lines where ground water comes up to the surface producing a pingo in the middle of a land mass.
What is frost heaving?
Frost heaving causes the surface of a road to become uneven due to the materials which it is built upon changing in volume during freezing and thawing.
