Geology and landscape around the Arctic Circle in Norway – Part II GEOLOGICAL GUIDE 26 27 Saltfjellet Between Svartisen and the Swedish border there is an extensive mountain area with varying scenery, ranging from barren mountains to fertile valleys. Saltfjellet lies furthest east. Here mountain plateau, broad valleys and rounded summits characterize the landscape which is developed in mainly granitic rocks. Further west, the height differences are accentuated and lofty mountain summits and narrow valleys prevail. The largest valleys, Saltdalen, Beiardalen, Bjøllådalen and Stormdalen extend in a mainly north-south direction and are aligned along the main structures of the bedrock which is here dominated by mica-schist and marble. The valleys usually follow marble belts and therefore have quite a luxurious and species-rich vegetation. The bedrock on Saltfjellet is characterized by light-coloured granitic gneisses. The main minerals are quartz, feldspar and a little mica. A special type of gneiss., containing the aluminium-rich mineral kyanite, is also found among the rocks on Saltfjellet. The mineral topaz is also found in the same zone. There are few exposures along the road over Saltfjellet, but on the northern slope, through Lønsdalen, there are several outcrops of these rocks in road-cuts. The great ice-sheet covering Scandinavia began slowly to release its grip on Saltfjellet a little over 9,000 years ago. The mountain tops were the first to become ice-free, and afterwards more and more of the mountain areas emerged as the glacier surface melted down and the ice-front retreated into the valleys. The ice mass was still enormous further east and extended to the Gulf. of Bothnia. Its highest part (ice divide) was far inside the Swedish border. The climate was quite warm at this time and melting proceeded relatively rapidly. Much melt water ran westwards from large areas as far as the ice divide. The ice and melt water have left distinct traces on Saltfjellet and the trained eye can read the ice melt story almost like an open book in this forest-free, open terrain. In the final phase, the ice masses moved northwards through Lønsdalen and down towards Saltdalen. The ice surface sloped to the north and melt water, which ran along the ice edge, formed channels and flowed in this direction. When buried ice relics later melted there were many depressions ('dead ice hollows') on the land surface which today may be water-filled. Hills or ridges of sand and gravel are common in such a terrain and formed in cavities, joints or tunnels where the melt water sought passageways between the last ice remnants. 28 29 The view northwards through Lønsdalen towards Solvågtind and Båtfjellet (in the background to the right). In the foreground, forested sand terraces, formed between the mountain side and the glacier during melting of the inland ice 9,000 years ago, can be seen. Photo: Asbjørn Rune Aa. 30 Reconstruction of the melting of the inland ice in the area north of the Arctic Circle Center about 9,000 years ago (Figure on the next page). A: Only the highest summits are exposed above the ice. The ice movement and drainage of the melt water are northwards. B: The glacier has melted down further. Channels form in the moraine cover where the melt water follows the contact between the ice and valley sides to the north. The ice is only 100-200 m thick at Semska-Sørelva. C: The Lønsdal stage. The Semska-Sørelva area is now ice-free. The retreat of the ice is halted and from Junkerdalen in the northeast there is a slight advance of the ice to the north which dams up Lønsdalen. Marginal ice terraces, small marginal moraines and melt water channels form. Today these are 'casts' of the ice margin. The ice tongues to the south remain stable. The melt water carries much gravel, sand and silt into a glacier dammed lake between Semska and Sørelva. The water finds an outlet to the north, at the foot of Kjemåfjellet. D: The ice disappears from the mountain pass, but relics may still be present along Lønselva. Melt water from the south drains northwards until the water divide at Stødi becomes ice-free so that water from the southerly glacial tongue flows southwards to Dunderlandsdalen. In the north the ice dams up small glacial lakes at a lower level at Sørelva and Dypenåga. Here sand and silt terraces are formed between the ice and valley sides. The small frame shows the area shown on the map of the superficial deposits on page 36. 31 32 Locality 1 - The Arctic Circle Centre The Centre is situated close to E6 on sand and gravel deposited by glacial rivers during the last ice age.l,700 million years old, underlie the superficial deposits and are their source, here two extremes of the geological time-scale meet old gneisses. All the rocks in the mountains near the Centre are Precambrian, but the superficial deposits here are younger than 100,000 years old. On Nasafjellet, which lies southeast of the Arctic Circle Centre, one can see the basement on which the Caledonian mountain chain rests. Here, weathering and erosion have carved down through the stack of nappes forming a so-called window. Through and within this window one can see the rocks over which the nappe units of the Caledonian mountain chain have been transported. The rocks around the Arctic Circle Centre originally belonged to this basement, but were detached by the thrust processes and now form the lowermost nappe unit. The Arctic Circle Centre is beautifully located in the mountainous terrain of Norway. View to the west towards Bolnatind. 33 Section through the upper part of the crust from the Arctic Circle Centre to the southeast towards the mountain area west of Krokstrand (to the left). The section shows how the rock units (nappes) are stacked up on each other by thrusting and subsequently folded, and how weathering and erosion have carved a "window" through them, so that the basement on which they rest is exposed at the present land surface. Locality 2 - Offersteinan. A Lappish sacrifical site 2 km north of the Arctic Circle Centre On Saltfjellet there are numerous so-called erratic blocks which were transported and deposited during the last ice age. Most are small and of local origin, but some are quite large. Some have been transpol1ed for long distances. As the ice melted and lost its capacity for transport, the blocks were left stranded. The largest of these are now prominent landmarks. Locality 3 - Saltfjellet at Stødi-Semska The 4 largest parking places (marked with P on the map) are located 8-16 kilometres north of the Arctic Circle Centre. A good view of the extensive superficial deposits can be obtained from all these places. The deposits are very thick and only occasionally can the bedrock be seen. 34 Old Lappish sacrificial site in the vicinity of three large erratic blocks at Stødi. The blocks are of the same rock as the bedrock on which they rest. They may however, have been transported many kilometres by the ice since this rock type is present many kilometres to the east and south-east. Locality 4 - Semska Large terraces are present on the valley floor east of the road. These were built up of gravel and sand carried by glacial melt water which flowed northwards during the Lønsdal stage (see fig. C, pages 31-32). The terraces terminate at the south end of a 10-20 m slope which is the 'cast' of the ice margin (ice contact-slope). The grave1 was transported to this place upon, within, or along the margin of the glacier and later washed forwards and deposited in terraces. Locality 5 - Semska-Sørelva Two large, north-south trending drumlins are present on this section, west of the road. They form marked ridges 20-40 m above their surroundings, and have a width of several 100 m. The largest is about 2 km long. 35 Superficial deposits and other traces of glaciation. Part of NGU's Quaternarygeological map Lønsdal 2128 III, scale 1:50,000 (each square on the map is 1 km2). The valley floor is covered by sand and gravel deposited during melting of the ice (orange), as terraces, ridges and hills. Fine grained glacial lake deposits (pale yellow) are also present. The valley sides and mountain plateau are characterized by thick till deposits which were earlier deposited under the sole of the inland ice (green). Elongate, streamlined ridges in the till surface (drumlins), reflect the direction of ice movement (black arrows). The whole area has numerous channels which are traces of melt water drainage 9,000 years ago (red symbols). 36 The gravel terraces on the valley floor were deposited about 9,000 years ago in front of a glacier tongue which dammed up the valley to the south (to the right). In the background, on the mountain side, some north-trending channels (towards the left) in which the water flowed at an early stage of the ice age melting can be seen. Photo: Harald Sveian. The largest and most prominent drumlin on the Saltfjellet, located near Sørelva close to E6. This is an elongate, streamlined moraine ridge oriented parallel to the ice movement direction. Photo: Harald Sveian. 37 Linear melt water channels in the till cover can be seen in the easterly valley slope north of Semska, the mountain in the background. In the foreground, large melt water deposits of sand and gravel are present. These form pronounced hills and ridges with depressions in between. Photo: Harald Sveian.