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Map showing the location of the Strait of Dover.

Cliffs at Dover

The Strait of Dover or Dover Strait (French: Pas de Calais, IPA: [pɑdə kalɛ], "Strait of Calais", Dutch: Nauw van Calais or Straat van Dover) is the strait at the narrowest part of the English Channel. The shortest distance across the strait is from the South Foreland, some 6 km (4 mi) north-east of Dover in the county of Kent, England, to Cap Gris Nez, a cape near Calais in the département of Pas-de-Calais, France. Between these two points – the most popular route for cross-channel swimmers – the distance is just 33 km (20 mi).

The strait lies at the east end of the English Channel, where it joins the North Sea. Its width is the shortest distance between France and England. On a clear day, it is possible to see the opposite coastline and shoreline buildings with the naked eye.

Most maritime traffic between the Atlantic Ocean and the North and Baltic Seas passes through the Strait of Dover, rather than taking the longer and more dangerous route around the north of Scotland. The Strait is one of the busiest international seaways in the world, regularly 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.^[1]

In addition to the intensive east-west traffic, the Strait is criss-crossed from north to south by ferries. Until the 1990s, these provided the only ground-based route for passengers and freight to cross it. The Channel Tunnel now provides an alternative route, crossing underneath the Strait at an average depth of 45 m (150 ft) underneath the seabed.

Satellite image of the Strait of Dover

NASA Satellite image December, 2002

NASA Terra Satellite image March, 2001

The Strait is believed to have been created through erosion. At one time there was land where the Strait is now, being a southeast extension of the Weald, joining what is now the island of Great Britain to continental Europe. The east end of this old longer Weald can be seen as the Boulonnais chalk area in the Pas de Calais. The predominant geology in the region on both the British and French sides and on the sea floor between to quite a depth into the earth's crust 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 Gris Nez on the French side of the Strait. This same rock also provided an excellent tunnelling medium for the Channel Tunnel.

Originally the Rhine flowed northwards into the North Sea as the sea level fell during the start of the first of the Pleistocene Ice Ages. However, the ice created a dam from Scandinavia to Scotland. 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 modern Strait of Dover. A narrow deeper channel along the middle of the Straits of Dover was the bed of the Rhine in the last Ice Age. In East Anglia there is a geological deposit which marks the old preglacial northward course of the Rhine.

However, a new study by Gupta et al. (2007)^{[2] [3]} suggests that the formation of the English Channel was formed not by gradual erosion, but by erosion caused by two major flooding events. 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 which broke catastrophically through a high weak barrier (perhaps chalk, or an end-moraines left by the ice sheet). Both floods cut massive flood channels in the dry bed of the English Channel, somewhat like what is seen in the Channeled Scablands in the USA.

In general crossing the straits other than in a conventional vessel is not encouraged. Many such crossings have been attempted including by pedalo, bathtub and more commonly by swimming. French law is stricter on such matters than UK law, so most such crossings originate in the UK.

• Battle of Dover Strait

1. ^ See The Channel Navigation Information Service (CNIS)
2. ^ Gupta, Sanjeev; Collier, Jenny S. & Palmer-Felgate, Andy et al. (2007), "Catastrophic flooding origin of shelf valley systems in the English Channel", Nature 448: 342-346.
3. ^ Europe cut adrift", by Philip Gibbard, pp 259-260, Nature, vol 448, 19 July 2007

• Channel Navigation Information Service
• Channel Swimming & Piloting Federation
• Channel Swimming Association
• Depth Chart showing straits and former course of Rhine

Coordinates: 51°01′17″N, 1°28′38″E