13. April 2008

BTS measurements at Iskoras, Finnmark

Contact person for additional information: Herman Farbrot

Text and photos by Herman Farbrot

 

Summit of Iskoras early March 4, 2008, looking east. Large areas of the mountain ridge is bare-blown.

 

Early March 2008 Karianne Staalesen Lille°ren and Herman Farbrot (both University of Oslo ) went to Northern Norway to investigate permafrost conditions through so-called BTS measurements (Basal Temperature of Snow cover).

The BTS method measures the ground surface temperatures beneath a thick snow cover (>80-100 cm) before the onset of melting. Due to the low thermal conductivity of snow, the ground surface temperatures reflect the thermal regime of the subsurface. Hence, low temperatures (below c. -3oC) indicate permafrost whereas temperatures close to 0░C indicate no permafrost.

The measurements were conducted at Iskoras, an east-west aligned mountain ridge, 20 km to the south of the city Karasjok. Iskoras is the highest mountain in Finnmarksvidda, south of the river Karasjohka. Close to the summit (597 m a.s.l.) the telecompany Telenor has established a antenna station (see photo above), where we kindly were allowed to stay overnight.

In our investigation, we focussed on the north and the south side of the mountain ridge. It was difficult to find sites with thick snow cover suitable for BTS measurements. However, a consistent picture of lower BTS values in the northfacing slope of the mountain compared to the southfacing slope emerged.

Preliminary results indicate no permafrost at snow covered sites in the southern slope, while permafrost may be present down to about 500 m a.s.l. at snow covered sites in the northern slope. The top plateau was mainly bare-blown with snow cover thicknesses of just a few cm. Here, a 10,7 m deep borehole was drilled September 2007 as part of the TSP Norway drilling campaign in Northern Norway . During the BTS campaign we for the first time obtained reliable ground temperature measurements from this site. Somewhat surprisingly there is no permafrost in the borehole. However, the lowermost sensor at 10.3 m depth showed distinct seasonal variation with temperatures both above and below 0░C. Hence, permafrost may be present at greater depth (assuming mean long-term borehole temperatures below 0░C).

Permafrost distribution in the region will be further investigated by geophysical investigations (electrical resistivity tomography and seismics) the coming summer.

Karianne Staalesen Lille°ren dressed up for BTS measurements and snowmobile ride in air temperatures close to -30oC.