Glacial erosion rates at Forsmark derived from Terrestrial Cosmogenic Nuclides – additional results: SKB TR-23-21

Adrian Hall, Jakob Heyman, Andy Hein

Research output: Book/ReportCommissioned report

Abstract / Description of output

This report presents results for a set of Terrestrial Cosmogenic Nuclide (TCN) samples taken from four sites close to the present shoreline at Forsmark. The sampling was undertaken to support a new study of glacial micro-forms and erosion rates during deglaciation. The samples extend the previously reported TCN dataset for the wider Forsmark region.
The sample set includes five paired samples from the top and base of rock steps and one new surface sample. Additionally, one new short (2.3 m) drill profile was obtained from Wave Rock in massive granite gneiss that previous work had shown to hold large TCN inventories. Glacial erosion was simulated based on the depth and time dependent production of 10Be and 26Al for a range of scenarios that include different start times and erosion modes yielding various production rates over time for the individual samples. The glacial erosion estimates reported here conform with previous estimates of depths and rates of glacial erosion for the Forsmark region but tend towards the lower end of previous estimates. For the depth profile, simulations starting at 624 thousand years ago (ka BP) yield constant glacial erosion rates of 0–25 mm/ka for the full set of samples at Wave Rock. Results from four of the step samples are consistent with formation of steps by block removal (‘plucking/quarrying’) during the last ice-covered period (35.4–10.8 ka BP). Erosion estimates for the last ice-covered period were compared between i) abraded surfaces at the summit of Wave Rock and ii) surfaces with micro-erosion forms that indicate combined abrasion and block removal at three other lower elevation sites in the vicinity of Wave Rock and at five other coastal sites. Estimated abrasion depths for the last ice cover period are low (23–46 cm) compared to combined abrasion and block removal depths (117–215 cm), showing that combined abrasion and block removal operated approximately four times faster than abrasion alone
Original languageEnglish
Commissioning body Svensk Kärnbränslehantering AB (SKB)
Publication statusPublished - 1 Nov 2023

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