Water controls the seasonal rhythm of rock glacier flow

Rock glaciers are creeping periglacial landforms experiencing strong acceleration during recent atmospheric warming and raising concerns with regard to their future behaviour and stability. High resolution kinematic observations show strong seasonal and multi-annual variations in rock glacier creep, but the linking mechanisms to environmental forcing remain poorly understood and lack quantitative models. Here we investigate the interaction between rock glacier creep and climatic forcing - temperature and precipitation - by developing a novel conceptual and numerical modelling approach. The model is constrained and the results are compared with data from the Dirru Rock Glacier (Vallis - CH). We are able to reproduce the observed velocity variations both in magnitude and phase on seasonal and inter-annual time scales. We find that water from liquid precipitation and snow melt, rather than air temperature, is the main driver of variations in rock glacier creep. Our results imply that the influence of water on rock glacier creep is fundamental and must be considered when investigating the historic and future evolution of rock glaciers. •Seven years of continuous in-situ observations for Dirru Rock Glacier.•Surface velocity is the combination of different superimposed signals.•Our process based model can reproduce velocity variations both in magnitude and phase.•Flow variations are governed by water, rather than air and ground temperature.•Rock glacier dynamics is complex and its coupling to climate strongly non-linear.