fjord

thumb|Geirangerfjord, [[Norway]] In physical geography, a fjord (also spelled fiord, a variant most common in New Zealand English; ) is a long, narrow sea inlet with steep sides or cliffs in a valley created by a former glacier, which has since become inundated with water. They are the glacial equivalent of drowned river valleys, known as rias. Fjords exist on the coasts of Antarctica, the Arctic, and surrounding landmasses of the northern and southern hemispheres. Areas with extensive fjords demonstrate an extreme example of the coastline paradox; Norway's coastline is estimated to be long with its nearly 1,200 fjords, but only long when excluding the fjords.

==Formation== thumb|A glacier in eastern Greenland flowing through a fjord carved by the movement of ice thumb|Illustration of how a fjord is created thumb|Fjords often continue as U-shaped valleys above sea level and freshwater fjord lakes: [[Sørfjorden (Hardanger) can be seen here transitioning into Sandvinvatnet and the Odda Valley. Odda sits on the isthmus, Folgefonna on the right.]] A true fjord is formed when a glacier cuts a U-shaped valley by ice segregation and abrasion of the surrounding bedrock. According to the standard model, glaciers formed in pre-glacial valleys with a gently sloping valley floor. The work of the glacier then left an overdeepened U-shaped valley that ends abruptly at a valley or trough end. Such valleys are fjords when flooded by the ocean. Thresholds above sea level create freshwater lakes. Glacial melting is accompanied by the rebounding of Earth's crust as the ice load and eroded sediment is removed (also called isostasy or glacial rebound). In some cases, this rebound is faster than sea level rise. Most fjords are deeper than the adjacent sea; Sognefjord, Norway, reaches as much as below sea level. Fjords generally have a sill or shoal (bedrock) at their mouth caused by the previous glacier's reduced erosion rate and terminal moraine. In many cases this sill causes extreme currents and large saltwater rapids (see skookumchuck). Saltstraumen in Norway is often described as the world's strongest tidal current. These characteristics distinguish fjords from rias (such as the Bay of Kotor), which are drowned valleys flooded by the rising sea. Drammensfjorden is cut almost in two by the Svelvik "ridge", a sandy moraine that was below sea level when it was covered by ice, but after the post-glacial rebound reaches above the fjord.