A fjord is a long, narrow inlet with steep sides or cliffs, created by a glacier. It is a deep, narrow and elongated sea or lake drain, with steep land on three sides. The opening toward the sea is called the mouth of the fjord, and is often shallow. The fjords inner part is called the sea bottom. Fjords are often set in a U-shaped valley with steep walls of rock on either side. They exist on the coasts of Antarctica, British Columbia, Greenland, Alaska, and Chile. Fjords are formed when a glacier retreats, after carving its way through a valley. The resulting valley floor forms a narrow, steep-sided inlet connected to the sea. The terminal moraine pushed down the valley by the glacier is left underwater at the fjord’s entrance, causing the water at the neck of the fjord to be shallower than the main body of the fjord behind it. The most famous fjords in Norway are the Geirangerfjord, the Aurlandsfjord, the Nærøyfjord, and the Lysefjord.