A fjord (or fiord) is a narrow inlet of the sea between cliffs or steep slopes, which results from marine inundation of a glaciated valley. Typical characteristics of a fjord include: a narrow inlet, a bottom glacially eroded significantly below sea level (allowing deep-draft vessels to navigate easily), steep-sided walls which continue to descend below the sea surface, greater depths in the upper and middle reaches than on the seaward side, and communication with the open sea.
Fjord is an English loan word taken from the Scandinavian term fjord, which derives from the Old Norse fjörðr (pronounced "fyurthr", now fjörður in Icelandic) meaning firth or inlet. The term fjord, although commonly used in Norwegian and Danish, is not universally used for naming fjords in other countries. Many fjords are called "canals", "inlets" and "sounds", e.g. Hood Canal and Burrard Inlet in the Pacific Northwest.
Fjords are found in locations where current or past glaciation extended below current sea level. A fjord is formed when a glacier downwastes, or melts faster than it is moving, after carving its typical U-shaped valley, and the sea fills the resulting valley floor. This forms a narrow, steep sided inlet (plunging up to 1900 m or 6300 ft below sea level) connected to the sea. Overdeepening of the glacier bed is common, which when combined with the terminal moraine often deposited at the fjord's entrance, usually results in shallower water at the neck of the fjord than in the main body of the fjord. Overdeepenings form near glacier heads or anywhere along the length of a glacier, but are prominent in downglacier reaches (i.e., areas where the glacier dropped significantly tend to be overdeepened at the base of the ice descent).
Fjords commonly have channels which follow the faults of the underlying rock, including occasional sharp corners. The valley at their head, in many cases, extends into the mountains. Sometimes a small residual glacier remains at the valley head. If there is no residual glacier, the river which flows in the valley will begin to build a delta at the head of the fjord; frequently this delta is the best place for farms and villages.
The shallow threshold, great depth and the protection afforded by the valley's sides generally means that fjords are excellent natural harbours. Consequently fjords often provide a home port to fishing fleets, and in industrialised locations have come to be used for fish farming and shipbuilding.
The circulation of the water in a fjord primarily depends upon the characteristics of the sill created by the terminal morraine and river flow into the fjord. Taller or longer sills can block deep intrusions of ocean water. The sill can also act as a hydraulic control. The deep inner basin of many fjords only gets replenished with new ocean water once a year, which can lead to Anoxic sea water. In addition to the sill, the combination of tides, winds, river flow and ocean density determine how frequently the deep water gets flushed.
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. They can be found 8 m (26 ft) below the surface in Acheron Passage, near Resolution Island. An underwater observatory in Milford Sound allows tourists to view them without diving.
Skerries are most commonly formed at the outlet of fjords where submerged glacially formed valleys at right angles with 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 1,600 km (1000 mi) 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 to Skagway, Alaska. Yet another such skerry protected passage extends from the Straits of Magellan north for 800 km (500 mi).
The principal mountainous regions where fjords have formed are in the higher middle latitudes where, during the glacial period, many valley glaciers descended to the then-lower sea level. The fjords develop best in mountain ranges against which the prevailing westerly marine winds are orographically lifted over the mountainous regions, resulting in abundant snowfall to feed the glaciers. Hence coasts having the most pronounced fjords include the west coast of Europe, the west coast of North America from Puget Sound to Alaska, the west coast of New Zealand, and the west coast of South America. Other areas which have lower altitudes and less pronounced glaciers also have fjords or fjord-like features.
The longest fjords in the world are:
Deep fjords include:
Even deeper is the Vanderford Valley (2,287 m or 7,503 ft), carved by the Antarctica's Vanderford Glacier. This undersea valley lies offshore, however, and so is not a fjord.
The Gulf of Kotor in Montenegro has been suggested by some to be a fjord, but is in fact a drowned river canyon or ria. Similarly the Lim bay in Istria, Croatia, is sometimes called "Lim fjord" although it is not actually a fjord carved by glacial erosion but instead a ria dug by the river Pazincˇica. The Croats call it Limski kanal which does not transliterate accurately to the English equivalent either.
Limfjord in the north of Denmark is a fjord in the Scandinavian sense, but is not a fjord in the English sense. In English it would be called a channel, since it separates the island of Vendsyssel-Thy from the rest of Jutland.
While the long fjord-like bays of the New England coast are sometimes referred to as "fiards", the only glacially-formed fjord-like feature in New England is Somes Sound in Maine.
The fjords in Finnmark (Norway), which are fjords in the Scandinavian sense of the term, are considered by some to be false fjords. Although glacially formed, most Finnmark fjords lack the classic hallmark steep-sided valleys of the more southerly Norwegian fjords since the glacial pack was deep enough to cover even the high grounds when they were formed.
Some Norwegian freshwater lakes which have formed in long glacially carved valleys with terminal moraines blocking the outlet follow the Norwegian naming convention; they are named fjords. Outside of Norway, the three western arms of New Zealand's Lake Te Anau are named fjords as well. Another freshwater "fjord" in a larger lake is Baie Fine, located on the northeastern coast of Georgian Bay of Lake Huron in Ontario. Western Brook Pond, in Newfoundland's Gros Morne National Park, is also often described as a fjord, but is actually a freshwater lake cut off from the sea, so is not a fjord in the English sense of the term.
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