Comparative numerical surface exposure-age dating (10Be and Schmidt hammer) of an early-Holocene rock avalanche at Alstadfjellet, Valldalen, southern Norway

ABSTRACT Application of calibrated Schmidt-hammer surface-exposure dating (SHD) to the run-out debris of a rock avalanche at Alstadfjellet, Valldalen, southern Norway, has yielded ages that are consistent within uncertainties with terrestrial cosmogenic 10Be surface-exposure ages for the debris. SHD calibration was based on young and old control sites that were, respectively, recent road cuts / rockfall boulders of known age, and Younger Dryas moraines for which 10Be ages had been obtained. Three SHD calibration equations were generated based on different correction factors for the 10Be ages from the moraines. The SHD ages (10.3 ± 0.59–11.1 ± 0.64 ka) for the run-out debris are from 1.1 ka to 1.3 ka older than the corresponding 10Be ages (9.2 ± 0.7–9.8 ± 0.7 ka). In addition, the former ages have a precision of 1.18–1.28 ka (95% confidence intervals) as opposed to 2.8 ka (2σ range) for the latter ages. This work demonstrates that calibrated SHD can be of comparable accuracy to and may have improved precision over 10Be ages, and should be given greater consideration and prominence in Quaternary dating studies.