Why are the highest peaks to be found in the Western Alps and not in the range which extends to the south and east? Are the glaciers under threat? Frédéric Herman gives his answers.
Associate Professor in the Faculty of Geosciences and Environment, Frédéric Herman (Institute of Earth Surface Dynamics) has just led a study into the relationship between plate tectonics and climate in the Franco-Swiss Alps. This research was published in March 2015 in Geology, the journal of the Geological Society of America.
When referring to this dynamic relationship which has been known to experts for twenty years, the researcher talks of tectonic-climate ‘linkage’. This new article underlines the efficiency of linkage in the Western Alps. While the range continues to move under the influence of plates in Austria and further east, subduction (plate convergence), it has been noted, stopped in the Franco-Swiss Alps a few million years ago. Could the Alps, like the Pyrenees, become old, dead mountains, slowly eroding beyond human observation?
“The rock which plunged beneath the mantle under the effect of subduction and which was pulling the range downwards has become detached and no longer has any influence to the west where Cervin, Mont Blanc and all the other 4000-metre plus peaks are to be found,” explains Frédéric Herman. Their summits are now rising at a rate of one to two millimetres a year, equivalent to two to four kilometres over the past two million years. As it was colder, glaciers were able to develop, points out the professor. What about more significant erosion in the west than the east, as demonstrated in the present study? Should this loss of volume of rock not in fact reduce the height of the peaks in question?
The professor responds by explaining that the erosion is much more marked in the west, as it is ice which is gouging out rocks as it moves, carving out valleys and filling them with sediment in a ‘self-defeating’ process, in other words a sort of glacial cannibalism. This loss is compensated for by the rebound effect which is the result of the cessation noted in the action of the plate which was pulling the mountain downwards. “The upward movement maintains the range at a sufficient height to create favourable climatic conditions for the development of glaciers,” sums up Frédéric Herman.
Effects of global warming
In contrast, the eastern Alpine range is still subject to subduction and to the downwards impetus of the plate once it had plunged beneath the Earth’s mantle. It should be remembered that the links between tectonics and climate were already established by research carried out into the formation of the Himalayas; the creation of such a large range as a result of the collision between India and Asia disrupted atmospheric circulation to the point where cooling was maintained and has continued over the past 50 million years.
What of global warming then? Will its acceleration melt the glaciers despite the rebound that is maintaining the peaks? The professor’s believes so, if the current rate of warming continues to increase as rapidly.
Frédéric Herman is at present working on other studies in the Alps of South New Zealand, which are subject to a conflicting process of elevation and erosion. He recently also explored the cordillera of the Patagonian Andes to gather samples which will be analysed in the UNIL laboratories. “We are also developing models of glacial erosion and analysing satellite images of glaciers. The models enable us to understand the physics of the erosion process and the satellite images enable us to measure the pace of glacial runoff,” he explains. His team is, in addition, interested in the Saint Elias range in Alaska. “These regions are characterised by extreme glaciation, high precipitation and active tectonics, thus producing a striking example of the linkage between tectonics and climate,” concludes this expert.