Paraglacial and periglacial processes drive headwall erosion in a deglaciating Swiss cirque

Abstract

Cirques are located at the top of the sediment cascade in high Alpine environments and are considered as glacial landforms. While glaciers erode the cirque vertically, the horizontal or headwall erosion usually is suggested to be a result of enhanced weathering and rockfall processes. Here, we quantified glacier dynamics of the Rothorn Cirque Glacier in the Swiss Alps since the Little Ice Age using glacier extent maps from Swiss glacier inventories in combination with own glacier extent mapping based on orthophotos. Furthermore, we quantified headwall erosion by rockfall processes using structure-for-motion photogrammetry for the period 2019 and 2023 and reanalysed rockfall data derived from laser scanning for the period 2016 to 2019. To analyse drivers of headwall erosion, we linked rockfall activity to glacier dynamics and previously published frost weathering intensities and rock permafrost distribution models. Finally, we compared our derived erosion rates to published headwall erosion rates from the European Alps. Our results revealed that cirque glacier retreat was accelerating, however, the role of paraglacial adjustment for headwall erosion was decreasing from the period 2016-2019 to 2019-2023. Therefore, our data suggests that frost weathering and rock permafrost occurrence were more important for headwall erosion. Headwall erosion rates for the Rothorn Cirque were lower than published erosion rates of the European Alps due to decreased importance of paraglacial adjustment. In summary, our data revealed that both paraglacial and periglacial processes drive headwall erosion in deglaciating cirques but the importance of drivers shifts from paraglacial to periglacial processes.