Strait of Dover
|Strait of Dover|
|Location||North Sea–English Channel (Atlantic Ocean)|
|Max. length||33.3 kilometres (20.7 mi)|
|Average depth||30 metres (98 ft)|
The Strait of Dover or Dover Strait (French: Pas de Calais [pɑdə kalɛ], literally Strait of Calais, Dutch: Nauw van Calais [nʌu vɑn kaˈlɛ]) is the strait at the narrowest part of the English Channel, marking the boundary between the Channel and North Sea, separating Great Britain from continental Europe. The shortest distance across the strait is from the South Foreland, 6 kilometres (3.75 miles) northeast of Dover in the county of Kent, England, to Cap Gris Nez, a cape near to Calais in the French département of Pas-de-Calais, France. Between these points lies the most popular route for cross-channel swimmers as the distance is reduced to 34 km (21 mi).
Most maritime traffic between the Atlantic Ocean and the North Sea and Baltic Sea passes through the Strait of Dover, rather than taking the longer and more dangerous route around the north of Scotland. The strait is the busiest international seaway in the world, used by over 400 commercial vessels daily. This has made safety a critical issue, with HM Coastguard maintaining a 24-hour watch over the strait and enforcing a strict regime of shipping lanes.
In addition to the intensive east-west traffic, the strait is crossed from north to south by ferries linking Dover to Calais and Boulogne. Until the 1990s these provided the only surface-based route across it. The Channel Tunnel now provides an alternative route, crossing beneath the strait at an average depth of 45 m (150 feet) below the seabed. The town of Dover gives its name to one of the sea areas of the British Shipping Forecast.
The strait is believed to have been created by the erosion of a land bridge that linked the Weald in Great Britain to the Boulonnais in the Pas de Calais. The predominant geology on both the British and French sides and on the sea floor is chalk. Although somewhat resistant to erosion, erosion of both coasts has created the famous white cliffs of Dover in UK and the Cap Blanc Nez in France. The Channel Tunnel was bored through solid chalk.
The Rhine (as the Urstrom) flowed northwards into the North Sea as the sea level fell during the start of the first of the Pleistocene Ice Ages. The ice created a dam from Scandinavia to Scotland, and the Rhine, combined with the Thames and drainage from much of north Europe, created a vast lake behind the dam, which eventually spilled over the Weald into the English Channel. This overflow channel was gradually widened and deepened into the Strait of Dover. A narrow deeper channel along the middle of the strait was the bed of the Rhine in the last Ice Age. In East Anglia there is a geological deposit that marks the old preglacial northward course of the Rhine.
A 2007 study concluded the English Channel was formed by erosion caused by two major floods. The first was about 425,000 years ago, when an ice-dammed lake in the southern North Sea overflowed and broke the Weald-Artois chalk range in a catastrophic erosion and flood event. Afterwards, the Thames and Scheldt flowed through the gap into the English Channel, but the Meuse and Rhine still flowed northwards. In a second flood about 225,000 years ago the Meuse and Rhine were ice-dammed into a lake that broke catastrophically through a high weak barrier (perhaps chalk, or an end-moraine left by the ice sheet). Both floods cut massive flood channels in the dry bed of the English Channel, somewhat like the Channeled Scablands or the Wabash river in the USA.
Many crossings other than in conventional vessels have been attempted, including by pedalo, jetpack, bathtub, amphibious vehicle and more commonly by swimming. French law bans many of these that British law does not, so most such crossings originate in England.
- "English Channel". The Cambridge Paperback Encyclopedia, 1999.
- See The Channel Navigation Information Service (CNIS)
- Gupta, Sanjeev; Collier, Jenny S.; Palmer-Felgate, Andy; Potter, Graeme (2007), "Catastrophic flooding origin of shelf valley systems in the English Channel", Nature 448 (7151): 342–346, Bibcode:2007Natur.448..342G, doi:10.1038/nature06018, PMID 17637667.
- Europe cut adrift, by Philip Gibbard, pp 259-260, Nature, vol 448, 19 July 2007