Fjord

A fjord is a long, deep, narrow coastal inlet drowned by the sea, carved by a glacier that scoured a U-shaped valley below sea level. Overdeepening by ice gives the seaward sill, a bedrock or moraine threshold shallower than the inner basin, which restricts deep-water exchange and can leave the inner basin stagnant and anoxic. Fjords are steep-sided, often hundreds of meters to over a kilometer deep, as in Sognefjord in Norway. They concentrate on glaciated high-latitude coasts: Norway, Chile, Greenland, New Zealand, Alaska. The shallow sill is a navigational and oceanographic control on circulation and under-keel clearance.