Can the retreat of the Morteratsch glacier be stopped?

All over the world glaciers are retreating. Shrinking of glaciers started in the middle of the 19th century (somewhat later at higher latitudes), and continues until today. There is little doubt that this is a response to global warming. In many regions the retreat has accelerated during the past few decades, notably in the Alps. Here, summer temperatures have risen at a rate 2.5 times greater than the global mean.

Figure 1. Vadret da Morteratsch in 2003, looking south. Front positions are indicated for selected years. The 2035 front position has been calculated for a scenario in which climate does not change.

Since 1860, the Morteratsch glacier, situated close to St Moritz in Switzerland (Figure 1) has retreated over a distance of 2700 m (550 m since 2000). The glacier is a major tourist attraction, and the gravel road to the glacier snout, visible in the photograph, is one of the most frequented hikes in Switzerland. Unfortunately, the glacier front has now retreated across a rock outcrop and can hardly be seen anymore from the end of the road. Pontresina, the community in which this glacier is located, fears that a significant further retreat of the Morteratsch glacier will negatively impact the attractiveness of the landscape. It therefore has commissioned a study to investigate possibilities to stop or slow down the retreat of this glacier.

Figure 2. The Diavolezza glacier under a fleece cover, photographed in September 2016 from the cable car.

The idea is partly inspired by the success of a glacier protection project on the Diavolezza ski run, which is situated close to the Morteratsch glacier. The Diavolezza glacier (Figure 2) is a very small one, but essential for the maintenance of the local ski run. Without the glacier, which fills a cirque, the upper part of the ski run would become too steep. The technique to protect the glacier is a simple one. Around mid-May, when snow accumulation normally stops, the glacier is covered by a sheet of white fleece (Figure 2). This protects the snow from melting, so that after the summer a significant fraction of the winter snowpack is saved for the next winter. In mid-October the fleece is removed again. This method has been applied now for more than 10 years, and the glacier has thickened by about 10 m.

However, the surface area of the Morteratsch glacier is two orders of magnitude larger than that of Diavolezza glacier, which makes it impossible to use a similar technique. After considering several alternatives, the best option appears to be the maintenance of an artificial snow cover through the summer in part of the glacier’s ablation area. The production of artificial snow is a trade-off between the availability of meltwater (summer half year) and sufficiently low temperatures (winter half year). Twenty years of data from the IMAU automatic weather station on the Morteratsch glacier have been used to run a snow production model, that calculates the amount of snow that can be deposited with a snow lance. Based on the surface energy budget, the model also calculates which part of the accumulated snow will melt again. The model simulation shows that it is possible to maintain a summer snow cover in the altitude range from 2300 to 2600 m. Melt water can be tapped from a natural, moraine-dammed lake. This lake is not visible in the photograph (blue arrow). The variations in the volume of this lake are currently being monitored, because it is a crucial parameter for water availability.

A second step in this study is to find out what a particular perturbation of the surface mass balance actually means for the future behaviour of the glacier. This can be investigated with a glacier flow model, carefully calibrated with observed glacier changes (in this case the length record over the period 1850 - 2015). A flowline model with a 20 m spatial resolution has been especially constructed for this purpose.

A mass balance history was then generated with an optimization method, by matching the observed and simulated length records. Integrating the calibrated model in time, with climatic conditions equal to the average over the past 15 years, reveals that the glacier will approach a steady state around the year 2040. The corresponding front position is indicated in Figure 1 by the black dashed line. The glacier will then be 1100 m shorter than today. A continuous mass balance perturbation of +1 m (water equivalent) per year in a 0.7 km2 region below the ice fall (the blue area in Figure 1) will make the glacier 150 m longer in 2040, and about 350 m in the long run.  This was considered as a minimum perturbation that is feasible and would have a modest but significant effect.

Further experimentation with the glacier model will provide more detailed answers about the expected effect of stronger mass balance perturbations over larger areas, for different climate change scenarios. This work is in full swing, and results will be presented at the EGU Assembly in April 2017.

Hans Oerlemans

Note: This work is carried out in close collaboration with Felix Keller (Academia Engiadina and ETH Zürich) and Martin Haag (Technische Fachhochschule Nordwestschweiz, Olten, Switzerland).

'Rettungsmission Morteratsch', Hans Oerlemans in the Tages-Anzeiger, Switzerland's largest newspaper.

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