Investigations on blockfields and related landforms at Blåhø (Southern Norway) using Schmidt-hammer exposure-age dating: palaeoclimatic and morphodynamic implications

ABSTRACT Schmidt-hammer exposure-age dating (SHD) was performed on blockfields and related landforms on Blåhø, Southern Norway. By developing a linear high-precision age-calibration curve through young and old control points of known age from terrestrial cosmogenic nuclide dating, it was possible to gain landform age estimates based on Schmidt hammer R-values. The aim of this study is to relate formation and subsequent stabilization of the landforms investigated to climate fluctuations since the Last Glacial Maximum (LGM) and to explore the palaeoclimatic implication of such periglacial landforms. The SHD ages range from 19.14 ± 0.91 ka for the Rundhø blockfield to 5.32 ± 0.73 ka for the lowest elevation rock-slope failure. The R-value frequency distributions obtained on the landforms studied indicate complex, long-term formation histories. Landforms above 1450 m a.s.l. share comparable SHD ages and seem to have stabilized during the Karmøy/Bremanger readvance (∼18.5–16.5 ka). The lower elevation rock-slope failures most likely occurred during the Bølling-Allerød interstadial (∼14.7–12.9 ka) and the Holocene Thermal Maximum (∼8.0–5.0 ka). The results contrast with the established model that rock-slope failures occur within the first millennia following deglaciation. Instead of the inferred ice coverage above 1450 m a.s.l. until 15.0 ± 1.0 10Be ka, our results suggest severe periglacial and ice-free conditions occurred earlier. Landforms above 1450 m a.s.l. do not show any form of reactivation during cold periods within the Late Glacial and Holocene. Our SHD results suggest that the landforms investigated were (at least partly) generated prior the LGM and survived beneath cold-based ice or were located on nunataks.