The U-shaped valley is chraracteristic of glacial erosion. The passage of the gigantic mass of a glacier marks the landscape with imposing tracks. Its abrasive power tears away the walls of blocks of rock. These are crushed and carried downstream. These are the moraines.
Glaciers are numerous during glacial periods (the last one ended 10,000 years ago). Numerous lakes and fjords bear witness to their presence, long after they have receded.
Thick sedimentary layers that have accumulated at the bottoms of fjordsand lakes conceal the true depth of the original valley.