DEFINITION OF PERMAFROST

Any soil, gravel, porous bedrock, or any part of

the regolith that has remained below freezing temperatures for

long periods of time, generally ranging from 2,000 to more

than 10,000 years. It underlies about one-fifth of the world’s

continental land area and is found in arctic, subarctic, and

alpine environments. Much of Canada, Siberia, Alaska, the

Tibetan Plateau, and even submerged areas around the Arctic

Ocean are underlain by permafrost. Most permafrost extends

to depths between 12 inches and 3,281 feet (30 cm–1,000 m)

and may be laterally continuous or discontinuous.

The upper surface of permafrost is known as the permafrost

table and is typically overlain by an active layer

consisting of up to a few meters of material that freezes

and thaws on an annual basis. The thickness of the active

layer is determined by soil type, latitude, and the presence

of standing bodies of water that tend to limit the layer’s

thickness. The active layer in permafrost layers tends to

become saturated with water since the meltwaters cannot

percolate downward through the permafrost. This results

in the layer becoming very weak, enhancing the formation

of landslides, solifluction lobes, and other slip features on

slopes.

The presence of permafrost in an area can make it

extremely difficult to construct roads, pipelines, buildings,

and other features that can change the temperature of the

ground, melting the permafrost layer and resulting in the

sinking or destruction of the artifact. This problem has been

growing in recent decades with increasing populations moving

into subarctic and arctic environments, and petroleum

exploration in places including northern Alaska. Houses

must be built on pillars that extend to bedrock, roads often

cannot be paved, and pipelines must be built either above

ground, or insulated and with special expansion/contraction

joints. Many recent studies have focused on the influence of

climate change and global warming on the distribution of

permafrost and have noted that permafrost regions contain

large amounts of trapped organic carbon that, if released to

the atmosphere, could increase CO2 levels, escalating global

warming.

See also SOILS.

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