Sonntag, 27. September 2009

The Permafrost Menace

The term permafrost is primarily associated with regions such as Alaska and Siberia, with a vegetation-free tundra, rock-hard frozen ground, and with the famous finds of well preserved carcasses of ice age mammals. But permafrost occurs in much wider geographic range, at least 23% of the Earth surface is influenced by permafrost.

Permanently frozen ground or permafrost is by definition material (bedrock or loose material), which remains at least for one year or two winters frozen, with temperatures below 0 ° C. Water, and so ice, is not necessary "needed" in permafrost, therefore called dry permafrost, but this kind of frozen ground plays geomorphological a minor role.

Climatic change has important effects on the distribution and the energy balance of permafrost , so influencing the amount of ice conservated in it. Permafrost occurence depends of various climatic (like temperature, insolation, precipitation and snowcover) and also from geomorphological (like exposition) and biological (like vegetation cover) factors - the role and interplaying between this factors is still poorly understand.
Permafrost in the middle latutudes lays only some degress under the melting point of water of 0°C, even a sligthly warming of the mean air temperature - and surface temperature, can heavily affect permafrost. The distribution diminuishes, and the depth of the active layer - the layer of permafrost that defrost´s during summer, increases.

How exactly permafrost reacts to the observed warming of 0,5°C during the last century in the Alps is still poorly known, and the exact mechanisms not understand. The strong retreat of glaciers is obvious, but permafrost was though to react much slower, because of the insolation effect of the covering debris layer. But observations of temperature profiles in drillholes showed that percoliating water, resulting from melting of more superficial ice, can "tranport" heat much faster in the underground.

Studying permafrost is a hard job, especially if it hides inside compact rock. PermaNet drill site in the valley of Schnals.

Morains and talus cones not only are habitats for specific, sometimes endemic animals and plants, but consists of loose debris hold together most time only by ice in the cavities between the boulders. Loosing permafrost can destabilise rock walls and debris, causing rockfalls and debris flows, and so putting infrastructures and humans life in danger. In the last 10 years the greatest rockfalls in the Swiss Alps occured in permafrost affected areas, one of the most spectacular in summer 2006 felt from the east-wall of the Eiger.

The rockfall of the Thurwieser mountain (3.652m, 46° 29` 45`` N, 10° 31` 28`` E) occurred on 19.09.2004 (first image befor, second after). 4,5 million cubic meters material felt on the underlying glacier and boulders up to 50 cubic meters slipped on it until 2000m a.s.l. The rockfall was caused probable by ice degradation.

The melting permafrost can influence the percolation and the paths that groundwater can take, so influencing springs. Observations in the european Alps and the Colorado Front Range showed also a change in the water chemistry in lakes and springs where permafrost features, like rock glaciers, occur in the catchement area. The change in water balance and presence can also effect the distribution of vegetation and the species richness of a habitat.

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