Straits of Dover
The Straits of Dover or Dover Straits are the seaway at the narrowest part of the English Channel. The Straits mark the end of the English Chanel and the beginning of the North Sea.
The shortest distance across the strait is from the South Foreland, 4 miles northeast of Dover in Kent, to Cap Gris Nez, a headland near Calais in France. Between these two points lies the most popular route for cross-channel swimmers as the distance is reduced to 21 miles.[1]
On a clear day, it is possible to see the opposite coastline and shoreline buildings with the naked eye, and the lights of land at night, as in Matthew Arnold's poem "Dover Beach".
Name
The name is of the Straits is sometimes written in the singular. The French call the passage the Pas de Calais, after their own town on the straits. The Romans knew it as the Fretum Gallicum or Fretum Britannicum or Fretum Morinorum.
Shipping traffic
Most maritime traffic between the Atlantic Ocean and the North Sea and Baltic passes through the Straits of Dover, rather than taking the longer and more dangerous route around the north of Britain. The strait is the busiest international seaway in the world, used by over 400 commercial vessels daily. This has made safety a critical issue and HM Coastguard maintains a 24-hour watch over the strait and enforces a strict regime of shipping lanes.[2]
In addition to the intensive east-west traffic, the strait is criss-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 underneath the strait at an average depth of 150 feet beneath the seabed.
Geological formation
The straits are believed to have been created through erosion. At one time there was land where the strait is now, a south-east extension of the Weald joining what is now Great Britain to Europe. The eastern end of this old longer Weald is the Boulonnais chalk area in northern France.
The predominant geology on both the British and French sides and on the sea floor between is chalk. Although somewhat resistant to erosion, such erosion of the chalk can be seen on both coasts as impressive sea cliffs, the famous white cliffs of Dover, and Cap Blanc Nez on the French side of the strait. This same rock provided an excellent tunnelling medium for the Channel Tunnel.
The Rhine 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 North Britain, and the Thames, joined by the Rhine, carried the drainage from much of northern Europe to create 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 Straits of Dover. A narrow deeper channel along the middle of the strait was the bed of the Thames-Rhine in the last Ice Age. In East Anglia there is a geological deposit that marks the old preglacial northward course of the Thames-Rhine.
However, a study in 2007 by Sanjeev Gupta and others[3][4] suggests that 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.
Unusual crossings
Many crossings other than in conventional vessels have been attempted, including by pedalo, 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 Kent.
Outside links
- Channel Navigation Information Service
- Channel Swimming & Piloting Federation
- Channel Swimming Association
- Depth Chart showing straits and former course of Rhine
References
- ↑ "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. 448. 342–346. doi:10.1038/nature06018. Bibcode: 2007Natur.448..342G..
- ↑ Europe cut adrift", by Philip Gibbard, pp 259-260, Nature, vol 448, 19 July 2007