Alps rivers such as the Danube have major tributaries flowing into them that originate in the Alps. The Rhône is second to the Nile as a freshwater source to the Mediterranean Sea; the river begins as glacial meltwater, flows into Lake Geneva, and from there to France where one of its uses is to cool nuclear power plants. The Rhine originates in a 30 square kilometre area in Switzerland and represents almost 60 percent of water exported from the country. Tributary valleys, some of which are complicated, channel water to the main valleys which can experience flooding during the snow melt
Geology of the Alps valleys repeatedly covered all of the Swiss plain and shoved the topsoil into the low rolling hills seen today. They scooped out the lakes and rounded off the limestone hills along the northern border. The last great glacier advance in the Alps ended some 10,000 years ago, leaving the large lake now known as Lake Neuchatel. The ice in this region reached some 1,000 m (0.6 mi) in depth and flowed out of the region behind Lake Geneva some 100 km (60 mi) to the South. Today large granite boulders are found scattered in the forests in the region. These