27. September 2008

First full year of TSP field measurements in Adventdalen, Svalbard

Contact person for additional information: Hanne H. Christiansen

Text and and figures: Håvard Juliussen and Hanne H. Christiansen, UNIS.

The TSP Norway project takes advantage of having staff based at UNIS in Longyearbyen in Svalbard, to be able to run several year-round permafrost related manual field measurements in the Adventdalen valley close to Longyearbyen in central Svalbard. The focus is on obtaining more detailed knowledge of active layer thermally controlled processes such as summer thawing and autumn and winter freeze-back and their climatic control. This is in addition to the many automatic measurements of e.g. the permafrost temperature now running in more than 10 boreholes, and automatic periglacial process monitoring in Svalbard .

Field measurements of ground resistivity going on in Adventdalen in autumn.

These days, the first full year of manual monthly ground electrical resistivity measurements at two sites in Adventdalen has been completed. By applying an electrical current to electrodes inserted in the ground and measuring the resulting electrical potential field (see photo above), an image of the ground electrical resistivity can be acquired (see diagram below). Since there is a considerable difference in electrical resistivity between frozen and thawed ground, the ground electrical resistivity image can be used to monitor ground thaw and freeze. The diagram below shows the relatively slow development of an increasingly thicker high-resistive, frozen layer (red colors) during autumn, reaching down to around 70 cm only in November. This shows the progressive ground freezing from the ground surface with the advance of the freezing front into the active layer. The entire active layer was only frozen during December. The blue colors indicate unfrozen conditions. This autumn more intensive daily to weekly field measurements are performed by UNIS master-student Angela Oswald for her master thesis.

Electrical resistivity of the upper part of the ground during 3 day in autumn 2007.

The development of the active layer has also been monitored by manual probing every 14 days of the 121 grid points in the UNISCALM grid, through the thawing season from end of May to mid September. Such measurements have been collected since 2000, and are part of the international CALM Network (Circumpolar Active Layer Monitoring Network). The mean active layer thickness on 16 September 2008 was 110 cm, the thickest recorded so far in the UNISCALM grid. Within the previous 8 years the active layer thickness in the UNISCALM grid has varied from 74 to 105 cm. This fairly large interannual temperature variation is mainly controlled by summer air temperatures and amount of summer radiation.

Several UNIS geology students have been involved in performing the many field measurements; many also joined the Permafrost Young Researchers Network.