Rock glaciers are comparatively climate-robust permafrost landforms. We estimated the energy budget of the seasonally thawing active layer (AL) of Murtèl rock glacier (Swiss Alps) based on a novel sub-surface sensor array. In the coarse blocky AL, heat is transferred by thermal radiation and air convection. The ground heat flux is largely spent on melting seasonal ice in the AL. Convective cooling and the seasonal ice turnover make rock glaciers climate-robust and shield the permafrost beneath.