A fjord or fiord ( or ) is a long, narrow inlet with steep sides, created in a valley carved by glacial activity.

Formation

see: Ice sheet dynamics#erosion The seeds of a fjord are laid when a glacier cuts a U-shaped valley through abrasion of the surrounding bedrock by the sediment it carries. Many such valleys were formed during the recent ice age. Glacial melting is also accompanied by a rebound in the earth's crust as the ice load is removed. In some cases this rebound may be faster than the sea level rise. Most fjords are, however, deeper than the adjacent sea; Sognefjord, Norway, reaches as much as 1,300 m (4,265 ft) below sea level. Fjords generally have a sill or rise at their mouth caused by the previous glacier's terminal moraine, in many cases causing extreme currents and large saltwater rapids (along the Pacific Northwest Coast of North America (see skookumchuck). Saltstraumen in Norway is often described as the worlds strongest tidal current. These characteristics distinguish fjords from rias (e.g. the Bay of Kotor), which are drowned valleys flooded by the rising sea.

Coral reefs

As late as 2000, some of the world's largest coral reefs were discovered along the bottoms of the Norwegian fjordsFact: date=September 2008 . These reefs were found in fjords all the way from the north of Norway to the south. The marine life on the reefs is believed to be one of the most important reasons why the Norwegian coastline is such a generous fishing ground. Since this discovery is fairly new, little research has yet been done. So far, only the deep sea diver who discovered the first reef at 60 meters has visited it, and even he has only been down three times. The reefs are host to thousands of lifeforms such as plankton, coral, anemones, fish, several species of sharks, and many more one would expect to find on a reef. However most are specially adapted to life under the greater pressure of the water column above it, and the total darkness of the deep sea.

New Zealand's fiords are also host to deep sea corals, but a surface layer of dark fresh water allows these corals to grow in much shallower water than usual. An underwater observatory in Milford Sound allows tourists to view them without diving.

Skerries

In some places near the seaward margins of areas with fjords, the ice-scoured channels are so numerous and varied in direction that the rocky coast is divided into thousands of island blocks, some large and mountainous while others are merely rocky points or rock reefs, menacing navigation. These are called skerries. The term skerry is derived from the old Norse sker, which means a rock in the sea.

Skerries are most commonly formed at the outlet of fjords where submerged glacially formed valleys perpendicular to the coast join with other cross valleys in a complex array. The island fringe of Norway is such a group of skerries (called a skjærgård); many of the cross fjords are so arranged that they parallel the coast and provide a protected channel behind an almost unbroken succession of mountainous islands and skerries. By this channel one can travel through a protected passage almost the entire 1,601.03 km route from Stavanger to North Cape, Norway. The Blindleia is a skerry-protected waterway that starts near Kristiansand in southern Norway, and continues past Lillesand. The Swedish coast along Bohuslän is likewise skerry guarded. The Inside Passage provides a similar route from Seattle, Washington and Vancouver, British Columbia to Skagway, Alaska. Yet another such skerry protected passage extends from the Straits of Magellan north for 800 km.