The Norwegian mountains: the result of multiple episodes of uplift and subsidence

The elevation of the mountains in Norway is geologically young. Much of the present-day land surface was buried below a thick cover of relatively young sediments in the early Miocene, 23 Ma, when Scandinavia started to be uplifted. Big river systems eroded deeply into the rising landscape and transported sand and gravel from Norway and Sweden to Denmark where the detritus was deposited in a large delta. In Norway, the erosion formed an extensive plain near sea level that included the present-day mountain plateau of Hardangervidda and extended across a thick pile of sediments that covered the present-day coastal areas of Norway. Hardangervidda was uplifted to its present elevation of about 1200 m after a second phase of uplift that began about 5 Ma, in the early Pliocene. The hard bedrock of Hardangervidda has preserved this part of the plain as an elevated plateau, but the part of the plain that extended across the sediments has been eroded away, exposing the underlying basement rocks. That re-exposed basement surface was shaped in the Jurassic when the climate was warm and humid. The basement rocks were weathered where rainwater seeped into fracture zones. Erosion of the weathered rocks has left a terrain of fracture valleys and hilly relief that contrasts with the sub-horizontal plain of Hardangervidda. This weathered landscape is today exposed on the slope between the west coast and Hardangervidda. While the elevation of the mountains is young, today's landscape has a long history.