Abstract. Debris-covered glaciers often exhibit large, flat tongues. Many of these glaciers show high thinning rates today despite thick debris cover. Due to lack of observations, most existing studies have neglected the dynamic interaction between debris cover and glacier evolution over longer time periods. The main aim of this study is to reveal this interaction by reconstructing changes of debris cover, glacier geometry, flow velocities, and surface features of Zmuttgletscher (Switzerland), based on historic maps, satellite images, aerial photographs, and field observations. We show that debris cover extent has increased from ~ 13 % to > 32 % of the total glacier surface since 1859 and that the debris is sufficiently thick to reduce ablation compared to bare ice over much of the ablation area. Despite the debris cover the volume loss of Zmuttgletscher is comparable to that of debris-free glaciers located in similar settings whereas changes in length and area have been small in comparison. Increased ice mass input in the 1970s and 1980s resulted in a temporary velocity increase, as well as a lowering of the upper margin of debris cover and exposed-ice area, and a reduction of ice cliffs. Since ~ 2001, the lowest ~ 1.5 km are stagnant despite a slight increase in surface slope of the glacier tongue. We conclude that the debris cover governs the pattern of volume loss without changing its magnitude, which is due to the large ablation area and strong thinning in regions with thin debris further up-glacier and in the regions of meltwater channels and ice cliffs. At the same time rising temperatures lead to increasing debris cover and decreasing glacier dynamics, thereby slowing down length and area losses.
Supplementary material to "The role of debris cover in the evolution of Zmuttgletscher, Switzerland, since the end of the Little Ice Age"
