Changing Alpine landscape: Lakes are replacing glaciers

As a result of climate change, Alpine glaciers are retreating. Today, they lose 2-3% of their surface area and volume each year. At this rate, there will be only very few remaining glaciers at high altitude by the end of the 21st century. Their retreat often leads to the formation of new mountain lakes.

More than a few puddles

A study by the Federal Office of the Environment concluded that the retreat of Alpine glaciers will create 500-600 basins susceptible to becoming lakes. Their total surface area might be between 50 and 60 square kilometres -- the lake of Thun, in comparison, has a surface area of 47 square kilometres. The depth of some of these lakes will surpass 100 meters and their volume will be greater than 10 million cubic meters, comparable with a medium-sized reservoir.

As part of NRP 61, researchers of the universities of Zurich and Berne as well as the EPF Lausanne studied this transformation of the Alpine landscape -- which will see the Konkordiaplatz of the Aletsch Glacier being replaced by a lake -- with regard to tourism, hydro-electric power and natural dangers. In one case study, researchers focused on Lake Trift in the Valley of Gadmen (Bernese side of the Susten Pass).

This lake appeared towards the end of the 1990s behind a glacial barrier and interrupted the path leading to the Trift mountain hut. To avoid the obstacle, the local authorities built a breathtaking suspension bridge, whose design was inspired by Nepalese rope bridges. This new bridge quickly became a tourist attraction. At this point, the Kraftwerke Oberhasli AG (KWO -- hydro-electric power company in the Grimsel area) re-activated an old cable car to bring tourists up to the area of the bridge. The mountain hut has received many more visitors as a result. While the retreating glacier represents an irreplaceable loss in terms of landscape, the loss in terms of tourism has been more than compensated by the attractive combination of glacier, lake and bridge. But what will happen once the glacier has disappeared completely in a few decades?

Limiting conflicts of interest

The new lake also has the potential of generating hydro-electric power. By building a dam at the level of the glacial barrier, the lake could be enlarged and integrated into the system of dams at the Grimsel (run by KWO). By considering the local hydrology and its evolution in the context of climate change, the researchers performed a quantitative analysis of several options -- from simple seasonal reservoir to integration into the existing turbine-pump-infrastructure -- and their impact in terms of hydro-electric power production. Irrespective of the chosen option, if a dam were built, it would considerably lessen the attractiveness of the site for tourists.

Whether the lake remains natural or becomes artificial, there is a significant risk of rock or ice avalanches due to the longterm destabilisation of slopes previously supported by the Trift glacier and the potential collapse of the current glacier tongue. Such avalanches can trigger a surge wave in the lake with disastrous consequences. The construction of a dam of adequate size could protect the area from floods and allow for the generation of power but it would reduce the appeal for tourists.

Legal questions regarding ownership and responsibility with regard to these new lakes are difficult to answer and the researchers urgently recommend integrated studies of the various lakes. The aim of such studies would be to develop visions focusing on the intelligent and sustainable use of the new lakes and landscapes. This will be particularly relevant in view of the renewal of concessions for many dams.

Reference: Wilfried Haeberli, Michael Bütler, Christian Huggel, Hansruedi Müller, Anton Schleiss, Frédéric Jordan, Therese Lehmann, Matthias Künzler, Yvonne Schraub, Stéphane Terrier (2012). Neue Seen als Folge der Entgletscherung im Hochgebirge: Klimaabhängige Bildung und Herausforderungen für eine nachhaltige Nutzung (NELAK). Forschungsbericht NFP 61.