Permafrost

Thickness

Where it is present since several glacial cycles, permafrost can be thick several hundreds of meters:

of 440 meters in Barrow, Alaska with approximately 750m in the Arctic Canadian
approximately 600 meters in Eastern Siberia with the maximum ones until more: 1000 meters in certain areas (mounts of Verkhoïansk).

Extension

Currently, it accounts for approximately 20% of the ground surface of the world, 25 million km ², of which a quarter of the emerged grounds of the Northern hemisphere.

The maximum last goes back: 20000 years, whereas all the northern half of France was cold and the sea much lower. The minima goes back: 6000 years. It is known as “Holocène optimum”.

Since except a warming of a few centuries in years 800 after JC, the summers of the northern hemisphere cooled causing a tendency to the territorial extension of permafrost, until the intrusion of the man in the climatic system.

In southern limit, permafrost at a temperature close to zero in summer could quickly melt. Canada considers that its southern limit can thus go up of 500 kilometers towards north in one century. A little more towards north, only the “active layer” will gain thickness in summer, inducing a growth of the vegetation, but also of the movements of ground, a hydrological modification and emissions of Méthane, the appearance of population of Moustique S. Certains models (Canadian) estimate that the significant effects will appear in the years 2025 to 2035.

The zone known as “activates”

It is the zone which thaws out in summer. It varies according to altitude and the latitude, but also in space and time at the rate/rhythm of the glaciations and warmings, sometimes brutally as soon as snowing up moves back and lets appear a dark ground which collects heat that the Albédo of the ices and snow returned towards the sky. This zone is generally deep today of a few centimetres to a few decimetres. With its southern limit, where it is less thick, it could extend quickly towards north. In the Scandinavian zones architecture rests today on piles inserted with several meters of depth, and it is recommended to preserve a vacuum under the house.

In the the Alps, the permafrost is found with the top of: 2500 meters on the Ubac S. a thaw of these zones could cause important crumblings.

In Swiss, the federal Office of environment (OFEV) published a chart and a brought up to date list of the particularly threatened inhabited areas. The dangers of crumblings exist especially for the localities which are located at the bottom of the valleys. Among them the commune of Zermatt appears, surrounded by three sides of mountain which rest on permafrost. The list also mentions Saint-Moritz, Saas Balen and Kandersteg. The probability that a large event occurs increases with the increasing cast iron of the ice. Risk carries not only on fact that important masses of rocks detach, but that those cause chain reactions which could generate damage in the inhabited areas, as it was the case in the Caucasus. In this area, in 2002, a rock collapse of a few million cubic meters involved a whole glacier with him, causing a gigantic landslide which completely destroyed a valley of more than thirty-three kilometers.

Moreover, this thaw, due to the Climate warming, could increase because of gas release with Greenhouse effect, of which the famous Méthane twenty-and-a time more effective than the CO2 but having one lifespan shorter than this last, from where the possible racing (even if one does not know precisely when) climatic machine .

The cast iron of the ice of permafrost is likely to create Thermokarst S, phenomena of solifluction and important movements of the grounds, which worries because about many constructions, as well as pipelines are posed without foundations on these grounds. Whole cities are built on permafrost like Iakoutsk posed on three hundred meters of ground and rocks frozen, where the annual average temperature increased 2°C in thirty years without in-depth observable consequence to date, according to the Institute of the permafrost founded in this city. Even if the ground does not melt, a differential warming between the surface and deep layers of ground or between elements more or less rich in water of the roadbases of ground could cause major damage by differential expansion.

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