Glacial Erosion Patterns in Valley Systems in Northern Sweden Investigated Using Cosmogenic Nuclides

Erosion patterns associated with glaciation of the Vávlájähkä , Dievssajávri, and Rávtasjávri valley systems in northern Sweden were investigated using cosmogenic nuclide (¹⁰Be and ²⁶Al) apparent exposure ages and inferred inheritance signals. Sequences of samples taken across valleys known to have been covered repeatedly by the Fennoscandian ice sheet revealed two primary patterns of erosion. In Vávlájähkä the exposure age pattern has consistent deglaciation ages (8-10 kyr) along the entire profile, indicating erosion of > ∼2 m at all sites during the last glacial cycle. At Rávtasjávri and Dievssajávri, deglaciation ages in the valley bottom contrast with apparent exposure ages two to four times older than deglaciation on the valley sides. Older ages on the valley sides are interpreted as reflecting cosmogenic nuclide inheritance due to limited (<2 m) erosion of the valley sides during the last glacial cycle. The pattern of erosion at Rávtasjávri and Dievssajávri indicates that in some locations glacial valley formation is a result of multiple glacial cycles rather than the result of topographic modification during a single glacial cycle. Initial data comparing hanging valley and trunk valley sites do not show distinct differences in apparent exposure ages. Slightly older ages on samples from hanging valley bottoms may suggest inheritance indicating lower erosion than trunk valleys, as would be expected given the marked topographic step between hanging and trunk valleys. Overall, initial data from this pilot study suggest that patterns of cosmogenic apparent exposure age data can in some cases provide constraints on spatial patterns of erosion and help refine understanding of the timing and scope of landform modification by glaciation.