Øverbøtjern

Centrally located in the Siljan valley, just east of Siljan’s center, lies Øverbøtjern.

This idyllic lake is a popular swimming spot and a great place to take a break when traveling between Skien and the Lågendal valleys. The lake is not directly part of the Siljan watercourse, but about 10,000 years ago, both the watercourse and the lake were part of a mighty fjord system that stretched from today’s coastline all the way up to Opdalen in Siljan. At that time, the great inland ice sheet that covered Norway during the last Ice Age had melted back, and seawater flooded into a landscape that had been weighed down by ice masses for thousands of years. Large amounts of clay and sand were deposited on the fjord floor, which has contributed to Siljan’s active agriculture today, with very fertile soil.

The upper limit of the fjord’s reach is called the marine limit. On a map of the marine limit, it is easy to see how the settlement in the Siljan valley has mostly developed on the former fjord floor, which is connected to the important resource of arable land. Above the marine limit, there are large forest areas-another natural resource that has been significant for Siljan. The watercourse that developed after the land rose and the fjord water retreated has played a central role in the historic timber floating down to Larvik.

The bedrock in Siljan dates to a special era in Norway’s geological history. At the transition between the Carboniferous and Permian periods, about 300 million years ago, there was intense volcanic activity in this area. This volcanic activity produced distinctive rocks such as larvikite and rhomb porphyry. Larvikite, Norway’s national rock, can be found in the north of Siljan and also in the area around Auen further south. Rhomb porphyry, which consists of ancient lava flows or rocks that solidified in cracks in the earth’s crust, is easily recognized by its light, angular spots and is found around Vindfjell and down toward Steinsholt.

The dominant rock type around Øverbøtjern is syenite, a rock that solidified deep beneath the volcanoes. Everything that once lay above the syenite has been worn away over the long time since the Permian. Ramsås, the steep hill on the eastern side of Øverbøtjern, consists of syenite, which is also the dominant rock in Siljan’s center. The scree below the hill is evidence that processes wearing down the landscape are still ongoing