Combining Cosmogenic Surface-Exposure and OSL Rock Surface Dating on a rock glacier in the Uinta Mountains (USA) - a comparative methodological study on exposure ages and a novel tool to constrain host rock erosion rates

Rock glaciers are common permafrost features in mountain landscapes around the globe. They pose a geo hazardous risk¹ sourcing large amounts of debris while also acting as aquifers storing large amounts of water². Due to limited dating efforts on rock glaciers, their long-term (i.e. centennial to millennial scale) dynamics and response to climate variability are poorly understood. Short term observations, via GPS, InSAR, UAVSAR, Lidar or feature tracking, show acceleration of flow rates of rock glaciers in all mountain regions³. Understanding past dynamics is key to project rock glacier behavior under future global warming.
This study combines cosmogenic radionuclide (CRN), and rock surface dating based on optically stimulated luminescence (OSL RSD) on a rock glacier in the Uinta Mountains (Utah, USA, 3300 m asl.). CRN dating of 8 quartzite boulders has been conducted by Munroe et al.⁴ and the same boulders were sampled for OSL RSD. 4 additional OSL samples of dark red quartzite were taken for increased dating resolution during fieldwork in 2024. The independent cosmogenic age control allows us to (i) test the applicability of OSL RSD in a high-altitude periglacial setting, (ii) investigate the sensitivity of the model parameters that are folded into the OSL bleaching-with-depth model and (iii) based on conceptual work by Sohbati et al.⁵ and Lehmann et al.⁶ to determine rock surface erosion rates of the quarzitic host lithology.

1.    Schoeneich, P. et al. Velocity Changes of Rock Glaciers and Induced Hazards. In Engineering Geology for Society and Territory - Volume 1, edited by G. Lollino, A. Manconi, J. Clague, W. Shan & M. Chiarle (Springer International Publishing, Cham, 2015), pp. 223–227.
2.    Jones, D. B., Harrison, S., Anderson, K. & Whalley, W. B. Rock glaciers and mountain hydrology: A review. Earth-Science Reviews 193, 66–90; 10.1016/j.earscirev.2019.04.001 (2019).
3.    Pellet, C. et al. Rock Glacier Velocity. In State of the Climate in 2023, edited by J. Blunden & T. Boyer (2024), pp. 44–46.
4.    Munroe, J. S., Laabs, B. J. C., Corbett, L. B., Bierman, P. R. & Handwerger, A. L. Rock Glacier Movement and Debris Transport Over Annual to Multi‐Millennial Timescales. JGR Earth Surface 129; 10.1029/2023JF007453 (2024).
5.    Sohbati, R. et al. Centennial- to millennial-scale hard rock erosion rates deduced from luminescence-depth profiles. Earth and Planetary Science Letters 493, 218–230; 10.1016/j.epsl.2018.04.017 (2018).
6.    Lehmann, B., Herman, F., Valla, P. G., King, G. E. & Biswas, R. H. Evaluating post-glacial bedrock erosion and surface exposure duration by coupling in situ optically stimulated luminescence and 10Be dating. Earth Surf. Dynam. 7, 633–662; 10.5194/esurf-7-633-2019 (2019).