Rockglaciers on the run – Understanding rockglacier landform evolution and recent changes from numerical flow modeling
Abstract. Rockglaciers are landforms indicative of permafrost creep and received considerable attention concerning their dynamical and thermal changes. Observed changes in rockglacier motion on seasonal to decadal timescales have been linked to ground temperature variations and related changes in landform geometries interpreted as signs of degradation due to climate warming. Despite the extensive kinematic and thermal monitoring of these creeping permafrost landforms, our understanding of the controlling factors remains limited and lacks robust quantitative models for rockglacier evolution in relation to their environmental setting. Here, we use a holistic approach to analyze the current and long-term dynamical development of two rockglaciers in the Swiss Alps. Site-specific sedimentation and ice generation rates are linked with an adapted numerical flow model for rockglaciers that couples the process chain from material deposition to rockglacier flow in order to reproduce observed rockglacier geometries and their general dynamics. Modelling experiments exploring the impact of variations in rockglacier temperature and sediment/ice supply show that these forcing processes are not sufficient for explaining the currently observed short-term geometrical changes derived from multitemporal digital terrain models at the two different rockglacier. The modelling also shows that rockglacier thickness is dominantly controlled by slope and rheology while the advance rates are mostly constrained by rates of sediment/ice supply. Furthermore, timescales of dynamical adjustment are found to be strongly linked to creep velocity. Overall, we provide a useful modelling framework for a better understanding of the dynamical response and morphological changes of rockglaciers to changes in external forcing.