Assessing the risk of hazards at Norwegian plateau glaciers in a warmer climate

The maritime plateau glacier Folgefonna (60^oN) is Norway's southernmost glacier. With its costal location the mass balance of the glacier responds to both changes in North Atlantic sea surface temperatures and changes in the westerlies transporting humid air towards the west coast of Norway. Many of the steepest outlet glaciers has a short (sub decadal) response time to climatic shifts and is therefore well suited for reconstructing high-resolution glacier fluctuations. Here we present results from lakes that have been cored in order to record past glacier variability based on sediments deposited in distal glacier-fed lakes combined with mapping and independent dating of marginal moraines. Based on ice radar measurements we have identified a number of possible glacier-dammed lakes, lakes with potential calving fronts and possible rerouting of meltwater drainage, all risks that will appear as the glacier melts in a warmer world. In depth we have investigated one outlet glacier with historical documented GLOFs that have formed repeatedly during periods with glacier extent similar to the present (13 times) and are thus used to pinpoint the Holocene variability in ELA to this level. Based on ice radar measurements and lake sediments we have in detail recorded the Holocene history at Folgefonna. We use past changes in glacier size to evaluate scenarios for how the glacier will respond to future warming with especially focus on meltwater routing relevant for the hydropower producers. Folgefonna melted away around 8000 yrs ago and reformed in mid-Holocene glacier growth (6400 cal. yr BP). First phase was characterized by gradual glacier expansion culminating in the glacial event at 2300 cal. yr BP. During the last 2000 years, Folgefonna expanded and decayed with significant decadal variability.