Permafrost

eneath a path (34 cm.) In the end of winter, 2006, the depth of freezing increased significantly.
The ground freezing in loamy sand and sand deposits (massive cryostructure) was much deeper
than in loamy and peat ones. Snow cover thickness was: early winter, 2004 – from 27 cm up to
70 cm (felling area), February, 2005 – from 40 cm (mean) up to 140 cm (gully). The two-level
composition of the river ice was found on the flood-plane and the river coast. The SFL
dynamics is caused mainly by the climate parameters, e. g.: the amount of negative degrees
during the winter 2004-2005 was 5800 deg.-hours while during 12 coldest days of January,
2006, it was 6100 deg.-hours, so the rate of freezing and the SFL depth has significantly
increased by the end of the freezing period. Investigations showed that the SFL dynamics is
strongly influenced by the rate of ground freezing, snow cover thickness, structure and
distribution depending on wind, relief and vegetation as well as landscape peculiarities and
ground properties.
Five year record on the progressing degradationof a lithalsa in the
Canadian Arctic
Georg Delisle 1 , Michel Allard 2 and Fabrice Calmels 2
(1.Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), Stilleweg 2, 30655 Hannover, Germany
2.Centre d’Études Nordiques, Université Laval, pavillon Abitibi-Price, Québec, QC, Canada, G1K 7P4)
Abstract: Numerous lithalsas have formed in marine clays which in the past have been exposed
to subaerial conditions in consequence of glacial rebound effects. Lithalsas are a valuable
indicator of past climate, since they are suspected to develop within a narrow band width of
mean annual air temperatures of between -4 to -6°C. A large population of lithalsas exists east
of the village Umiujaq near the eastern shoreline of the Hudson Bay. The structure and thermal
decay of one lithalsa due to climatic warming in the Canadian Arctic has been investigated and
monitored since the year 2000 jointly by teams of Laval University, Quebec, Canada, and of the
Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), Hannover, Germany. The
investigated structure has a diameter of about 50 m and rises on average by about 2.5 m above
the surrounding wetlands. A continuous record of thermal data from six bore holes, the results
of borehole investigations and on drill cores from within the lithalsa are now available.
The temperatures in the main mass of the lithalsa are between -0.8°C to -0.2°C.
Nevertheless, a highly complex image of the internal temperature field has emerged from the
temperature records. An estimated volume of 200 m³ of ice was lost from the interior of the
palsa during the last three years. The volume loss expresses itself by subsidence of the lithalsa
surface. A crescent-shaped pond has started to develop and the outline of a future thermokarst
lake surrounded by a rim has begun to show up. Ground subsidence actually affects about one
half of the lithalsa, creating a hollow that traps snow and water, therefore making the depressed
area a very effective heat source throughout the year which will speed up the thermal decay of
the lithalsa.
The rate of climatic warming in the area of investigation has slightly slowed down from
measured rates of 0.4°C per decade from 2000 to 2002 to currently about 0.2°C per decade
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