Right after the second category three climb, the Col des Mosses, we descend back into the valley of the Rhône, this time before it empties into the southeastern side of Lake Geneva (Lac Léman) — the river that we saw in France emerges from the southwestern side of the Lake.
The area of the lake that we pass today is yet another Ramsar site: Les Grangettes, the Rhône delta in the lake. The actual inflow of the river into the lake is an impressive sediment plume.
Most of the delta of the river is composed of sediments on the bottom of the lake. Where exactly those sediment end up depends on the relative density of the lake waters and the river water (Moscariello 2012). When the river water is denser than the warm waters on the surface of the lake (the epilimnion) but lighter than the cooler deep waters (the hypolimnion) the sediment-heavy river water floats on the boundary between the two lake layers and is transported out into the lake. The Coriolis force pushes these waters to the north, and the fine silt sediment settles out in a fan to the north. When the river water is denser than the hypolimnion, the river water flows down to the lake bottom, where it carves out a network of submarine channels.
Moscariello, Andrea, Frédéric Arlaud, Yosef Akhtman, Flavio S. Anselmetti, and Ulrich Lemmin. “Searching the Rhone delta channel in Lake Geneva since François Alphonse Forel.” Archives des Sciences 65 (2012): 103-118.