Perma frost

By sreeremya.s

Assistant professor

• Permafrost grows by freezing from its base downward

• or, when new material is added to the ground

• surface, from the top upwards, or by a combination of

• these processes. The first permafrost on Earth likely

• formed prior to or during the first ice age about 2.3

• billion years ago, and its occurrence, distribution, and

• thicknesses have varied in response to repeated ice ages

• throughout Earth’s history.

There is scientific and geotechnical interestin permafrost principally because it contains ice,is close to its thawing point, and is sensitive tochanges in surface conditions caused by humanactivities and climate. Temperatures in permafrostpresent retrievable records of past climate, andclimatic change commonly leaves an imprint on thestratigraphy of ground ice. Ice-rich permafrost containsice in excess of the water content at saturation,with the ice masses commonly distributed as lenses,millimeters to centimeters in thickness, within theground. Massive ground ice with dimensions typicallyfro

• Permafrost, ground that remains at or below 01C

• for two or more years, underlies about a fifth

• of the land surface of the Earth. Permafrost terrain

• consists of an active layer at the surface that freezes

• and thaws each year, underlain by perennially frozen

• ground.

The top of permafrost is at the base of theactive layer, and the base of permafrost occurs wherethe ground temperature rises above 01C at depth(Figure 1).The first scientific reports on permafrost werepublished in the 1830s by the Royal GeographicalSociety of London.

These papers reported the thicknessof frozen ground in a well at Yakutsk, Russia, andprovided instructions to officers of the Hudson’s BayCompany on describing the phenomenon. The firstsystematic study published in English of perenniallyfrozen ground was prompted by strategic considerationsinWorldWar II, when the Alaska Highway wasbuilt through northern British Columbia andYukon toAlaska, with the associated Canol Pipeline. At that