THE DESTINY OF UPPER LAKES
Mountain streams erode the terrain they cross and carry sand, gravel and pebbles. This alluvium threatens the lakes in which they are deposited. When the torrent flows into the waters of a high altitude lake, the speed of its course suddenly slows down. The coarsest and heaviest alluvium then samass at the level of the mouth. The lighter ones remain in suspension in the water, they settle a little further to the bottom of the lake. The deposits thicken over time and progress towards the middle of the lake. These two dynamics led, inexorably, the lake of Cubourré to evolve into a wetland at altitude. The upstream of the Lacustre basin filled with sediments while the downstream was filled by accumulation of peat. On the surface of the lake, peat tremors were developing. When they broke away, they formed floating rafts.
FROM LAKE TO WETLAND...
Since their formation at the end of the last glaciation, the lakes of Plagnes and Cubourré have evolved into wetlands.
If you go to famònt de Cubourré (in the direction of the Tinderets refuge and the Ardens chalets). you will see a stream meandering a flat wetland. This plateau was originally a glacial lake