Lakes and glaciers of the Alps
TODAY glaciers cover 3,200 km2 ofthe Alps--roughly the same area as those of Scandinavia and some twenty times more than those of the Pyrenees, but barely one-tenth of the maximum glacier area during the Pleistocene Epoch. The erosive action of this enormous mass of ice as it advanced and retreated gradually shaped most of the lake basins in the Alps, although tectonic occurrences also contributed to the formation of many such basins including those of the Bodensee and the Traunsee.
But one thing is certain. The basins ofsome Alpine lakes were formed very long ago, possibly even in the Tertiary Period (more than 1.5 million years ago), whereas the present lake stage may be scarcely older than 18,000 years.
So one of the most interesting questionsfacing limnology, the scientific study of lakes, is how our modern lakes developed. So far our knowledge of their history is fragmentary. One piece of information was gleaned when construction work on the highway near the Mondsee in Upper Austria brought to light lake sediment from the last interglacial period (between the Riss Glacial Stage and the Wurm Glacial Stage). This revealed not only that the water level of the Mondsee was then 60 metres higher than it is today but also that it formed part of a much bigger lake embracing both the Irrsee and the Attersee. It has also been established that the water level of Lake Waginger in Bavaria has fallen 15 to 20 metres since the Wurm Glacial Stage.
On the other hand, archaeologists areconvinced that the construction methods used in Alpine lakeside dwellings between 4,200 and 5,900 years ago were possible only if the water level was several metres lower. But this assertion, which would imply the absence of outflows and therefore a higher salt content in the lakes in question, has not been confirmed by limnology.
There were also--and no doubt stillare--a number of lakes with a lifespan of no more than a few thousand years. They largely originated during the retreat of the great glaciers, as in the Salzach and Enns valleys, which were filled with boulders and debris within this short period. Masses of water could also be dammed up behind terminal moraines and lead to the flooding of valleys. This phenomenon, which is found more rarely in the Alps than in some other mountain regions, led to catastrophe in the Andes not long ago.
Some small lakes connected with theadvance and retreat of glaciers have an even shorter lifespan. Since the last maximum glacier level around the middle of the nineteenth century, many lakes have emerged in this way and in some cases disappeared, including the small Eisrandsee near Hochkonig (Salzburg), which completely emptied through a newly formed ice tunnel in September 1934. …