Past and future impact of glacial erosion in Forsmark and Uppland. Final report

The following report constitutes a final report of a comprehensive study on denudation and glacial erosion conducted at Forsmark and in the surrounding Uppland province, Sweden, between 2015 and 2019. The aim was to quantify the amount of past denudation at the Forsmark site and the broader Uppland region, with special focus on glacial erosion, by employing a range of methodologies. The methods included geomorphological mapping and analysis of the bedrock surface and Quaternary deposits, cosmogenic exposure dating, bedrock fracture mapping, and shallow bedrock stress modelling. The results were also used together with results from a long-term climate modelling study to quantify the potential amount of glacial erosion at Forsmark over the coming one million years. The study was initiated by Jens-Ove Näslund (SKB) and it was jointly designed by Jens-Ove Näslund, Adrian Hall (Stockholm University), Karin Ebert (Södertörn University), Bradley Goodfellow (Stockholm University, SGU), Clas Hättestrand (Stockholm University), Jakob Heyman (University of Gothenburg) and Arjen Stroeven (Stockholm University). Adrian Hall coordinated the scientific work within the study, and also conducted the studies on long-term burial and erosion history (Chapter 2) and glacial erosion (Chapter 4). Karin Ebert developed the digital elevation models of the unconformity and derived the glacial erosion estimates derived from summit erosion surfaces. Bradley Goodfellow contributed across the project and conducted the study of topographic stress perturbation, with mathematical modelling by Seulgi Moon (University of California, Los Angeles) (Chapter 3). Clas Hättestrand developed geomorphological maps of the unconformity and of glacial bedforms. Maarten Krabbendam (British Geological Survey) contributed to Chapter 2 on the longterm burial and erosion history and to Chapter 4 on glacial erosion and mapped landforms associated with glacial ripping in Uppland. Sample site selection and cosmogenic nuclide sample collection was carried out by Jakob Heyman, Bradley Goodfellow, Arjen Stroeven, Marc Caffee and Adrian Hall. Jakob Heyman conducted the modelling of cosmogenic nuclide erosion and burial histories. Bradley Goodfellow was involved in cosmogenic nuclide sample preparation at Purdue University. Reporting and interpretation of cosmogenic nuclide results in Chapter 5 was done by Jakob Heyman, Arjen Stroeven and Bradley Goodfellow. All authors contributed to the final revision of the report. The study includes several additional important contributions. Marc Caffee (Purdue University) was responsible for all cosmogenic isotope laboratory analyses and guided and participated in the discussions of interpretation of results (Chapter 5). Stephen Martel (University of Hawaii) and Taylor Perron (Massachusetts Institute of Technology) were involved in the fracture mapping and modelling (Chapter 3). Mikis van Boeckel (Stockholm University) produced many of the figures in the report from digital elevation model data from the Swedish mapping, cadastral and land registration authority (Lantmäteriet) and SGU. In connection to the present study, two additional studies have been performed employing similar methods (e.g. geomorphological analysis and cosmogenic exposure dating) for studying the sub- Cambrian unconformity in the Trollhättan area in south-western Sweden. The two associated studies will be published in separate reports (Goodfellow et al. 2019, Hall et al. 2019a). The results will be used, together with other published scientific information, for constructing future scenarios of climate and climate-related processes in SKB’s work on assessing long-term safety of nuclear waste repositories in Sweden. The safety assessments performed for the planned repository for spent nuclear fuel in Forsmark, Sweden, cover a total time span of one million years. Since this time span covers the timescales relevant for glacial cycles, the effect of future glacial erosion needs to be analysed in the safety assessments. In this context, the present study provides important results on the potential amount of glacial erosion that may be expected in the topographical, geological, and glaciological setting of the Forsmark site. A separate study models changes in climate over the next 1 million years and has been published ahead of this report (Lord et al. 2019).