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Glossary of Permafrost Terms

Glossary of Terms


Active layer — the top layer of the ground, that freezes and thaws.


Adaptation- any action that reduces the negative impacts of climate change or takes advantage of potential new opportunities.


Climate- weather conditions over a long period of time.


Climate change- a change in the distribution or irregularity of weather patterns that carries on for a long time.


Excess ice — the extra volume of ice in the ground over and above the total amount of water under natural unfrozen conditions.


Frost boil- small mounds of earth or mud formed by frost action.


Frost heave — the upward or outward movement of the ground surface caused by ice formation in the soil.


Frost jacking — upward movement of objects in the ground due to freezing and thawing.


Frozen ground- ground containing ice


Glacier- a slow-moving mass or river of ice formed by compacted snow over a period of time.


Hummocky ground- land surface covered with small mounds.


Ice lens — a mainly horizontal, lens-shaped body of ice.


Ice-rich permafrost — permafrost containing excess ice.


Ice wedge-  ice in a triangle shape pointing downward below the active layer, often occurring with regular-shaped patterns of ground or vegetation.


Icing- sheets of ice on the ground or on top of lake or river ice, caused by freezing water from the ground.


Pad and wedge- stacks of wood that hold a building off the ground and keep the building level. These blocks of wood should be on a gravel pad and may need annual adjustment using wedges to keep the building level.


Permafrost — ground (soil, rock, water, and ice) that remains at or below 0°C for several years. Permafrost may not be permanent, because changes in the climate or landscape may cause the temperature of the ground to rise above 0°C.


Screw jacks- adjustable jacks that hold a building off the ground and keep the building level. These jacks are placed on wooden platforms on a gravel pad to spread the weight. Annual maintenance may be needed.


Space frames- a web of aluminum tubes that spread the weight of a building onto many points. This system is often used when there is a high chance of unstable permafrost in the ground underneath.


Steel piles — long slender columns drilled deep into the ground to provide support for buildings. Piles that are not drilled deep enough into the permafrost can shift up and down during the year as permafrost freezes and thaws.


Solifluction- slow downslope movement of wet ground, also known as a landslide.


Subsidence- downward movement of ground after thawing.


Talik — an area of unfrozen ground in permafrost terrain, often under lakes or rivers.


Thaw-sensitive permafrost —frozen ground that may experience significant downward movement if it thaws.


Thaw Slump- frozen ground that thaws and caves in causing a hole.


Thermosyphon — a refrigeration device using no electricity, that transfers heat from the ground to the air and helps keep the area below a building cool.  


Thermokarst -- The annual thawing of the active layer that results in soil flow and the soil surface collapsing.


Weather- the current state of the atmosphere. Weather is often what you think of when you look outside on a given day.