A tarn (or corrie loch) is a mountain lake or pool, formed in a cirque excavated by a glacier. A moraine may form a natural dam below a tarn. High altitude snowy mountain peak. Dangerous summit and cliffs. U-shaped shape trough troughs valleys, with steep, straight sides and a flat or rounded bottom (carved V-shaped in cross-section). Glaciated down a slope carving the valley by the action of scouring. Alpine alp climate highland sediment sediments crater mountainous hilly peaks sharp rocky rock wall summits snow ice moraine cliff fly flying glaciation. 4K UHD 3840×2160 30p.