Strait of Dover#Geological formation
{{Short description|Strait at the narrowest part of the English Channel}}
{{Use British English|date=November 2012}}
{{Use dmy dates|date=January 2020}}
{{redirect|Pas de Calais|the French department|Pas-de-Calais}}
{{Infobox body of water
| name = Dover Strait
| other_name =
| image = File:France manche vue dover.JPG
| caption = View from France across the Strait of Dover towards the English coast
File:Strait of Dover map.png
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| location = North Sea–English Channel (Atlantic Ocean)
| coords = {{coord|51|00|N|1|30|E|type:waterbody_dim:300000|display=inline,title}}
| type = Strait
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| basin_countries = France
United Kingdom
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| min_width = {{convert|20.5|mile|km}}
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| depth = {{convert|150|ft}}
| max-depth = 68 m (223 ft)
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The Strait of Dover or Dover Strait,{{efn|{{langx|fr|Pas de Calais}} {{IPA|fr|pɑ d(ə) kalɛ||Fr-Paris--Pas-de-Calais.ogg}}, "Strait of Calais"; {{langx|pcd|Pas d'Calés}}; {{langx|nl|Nauw van Calais}} {{IPA|nl|ˈnʌu vɑŋ kaːˈlɛː|}} or, less used, {{lang|nl|Straat van Dover}}.}} historically known as the Dover Narrows, is the strait at the narrowest part of the English Channel, marking the boundary between the Channel and the North Sea, and separating Great Britain from continental Europe. The shortest distance across the strait, at approximately {{convert|20|mi|km|abbr=off}}, is from the South Foreland, northeast of Dover in the English county of Kent, to Cap Gris Nez, a cape near to Calais in the French département of Pas-de-Calais. Between these points lies the most popular route for cross-channel swimmers.{{cite book |editor1-last = Crystal |editor1-first = David |title = Cambridge Paperback Encyclopedia |date = 1999 |publisher = Cambridge University Press |isbn = 978-0521668002 |pages = 1080 |edition = 3rd |language = en |chapter = English Channel }} The entire strait is within the territorial waters of France and the United Kingdom, but a right of transit passage under the United Nations Convention on the Law of the Sea allows vessels of other nations to move freely through the strait.{{cite book |last1 = López Martín |first1 = Ana G. |title = International Straits: Concept, Classification and Rules of Passage |date = 2010 |publisher = Springer Science & Business Media |isbn = 9783642129063 |page = 95 & 102 |edition = Illustrated |language = en }}{{cite journal |last1 = Glegg |first1 = G |last2 = Jefferson |first2 = R |last3 = Fletcher |first3 = S |editor1-last = Sheppard |editor1-first = Charles |editor2-last = Galgani |editor2-first = Francois |editor3-last = Hutchings |editor3-first = Pat |editor4-last = Quintino |editor4-first = Victor |title = Marine Governance in the English Channel (La Manche): Linking Science and Management |journal = Marine Pollution Bulletin |date = 30 June 2015 |volume = 95 |issue = 2 |pages = 707–718 |doi = 10.1016/j.marpolbul.2015.02.020 |pmid = 25819447 |language = en |doi-access = free |hdl = 10026.1/3662 |hdl-access = free }}{{cite book |last1 = Van Dyke |first1 = Jon M. |chapter = Transit Passage Through International Strait |editor1-last = Chircop |editor1-first = Aldo |editor2-last = McDorman |editor2-first = Ted |editor3-last = Rolstons |editor3-first = Susan |title = The Future of Ocean Regime-Building |date = 2009 |publisher = Brill (1618) |isbn = 978-9004172678 |pages = 175–232 |language = en }}
On a clear day, it is possible to see the opposite coastline of England from France and vice versa with the naked eye, with the most famous and obvious sight being the White Cliffs of Dover from the French coastline and shoreline buildings on both coastlines, as well as lights on either coastline at night, as in Matthew Arnold's poem "Dover Beach".
Shipping traffic
File:AIS Manche Est.png display showing traffic in the strait in 2006]]
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 one of the busiest international seaways in the world, used by over 400 commercial vessels daily. This has made traffic safety a critical issue, with HM Coastguard and the Maritime Gendarmerie maintaining a 24-hour watch over the strait and enforcing a strict regime of shipping lanes.{{cite web |url = http://www.mcga.gov.uk/c4mca/mcga-hm_coastguard/channel_navigation_information_service_(cnis).htm |title = The Channel Navigation Information Service (CNIS) |archive-url = https://web.archive.org/web/20071017200620/http://www.mcga.gov.uk/c4mca/mcga-hm_coastguard/channel_navigation_information_service_(cnis).htm |archive-date = 17 October 2007 }}
In addition to the intensive north-east to south-west traffic, the strait is crossed from north-west to south-east by ferries linking Dover to Calais and Dunkirk. Until 1994 these provided the only route across it except for air transport. The Channel Tunnel now provides an alternative route, crossing beneath the strait at an average depth of {{cvt|45|m|ft}} below the seabed.
The town of Dover gives its name to one of the sea areas of the British Shipping Forecast.
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==Geological formation==
The formation of strait was through scouring by erosion. It had for many millennia (since the last warm interglacial) been a land bridge that linked the Weald in Great Britain to the Boulonnais in the Pas de Calais. Though pitted by troughs and rivers, the English Channel was almost mainly land at the height of the last ice age.{{Cite encyclopedia |title=English Channel {{!}} channel, Europe |encyclopedia=Encyclopædia Britannica |url=https://www.britannica.com/place/English-Channel |access-date=16 May 2017 |language=en |archive-url=https://web.archive.org/web/20170403222035/https://www.britannica.com/place/English-Channel |archive-date=3 April 2017 |url-status=live}} The predominant geology of both and of the seafloor is chalk. Although somewhat resistant to erosion, erosion of both coasts has created the famous white cliffs of Dover in the UK and the Cap Blanc Nez in France. The Channel Tunnel was bored through solid chalk – compacted remains of sea creatures and marine-deposited, ground up calciferous rock/soil debris.
The Rhine (as the Urstrom) flows northeast into the North Sea as the sea (covering most of the Netherlands) fell during the start of the first of the Pleistocene Ice Ages. The new ice unusually 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 followed by further scouring became recognisably the Short Straits (an alternative name for this strait) about 425,000 years ago. A narrow deep channel along the middle of the strait is the remnants of the main (summer) outflow of the northern Ustrom glacial lake (a collect for other then-seasonal rivers, in winter iced up, such as the Thames and Weser) in the last Ice Age. A deposit in East Anglia marks the old preglacial northward course of the Urstrom-Thames when it also drained Doggerland. The deep sea floor east of Lincolnshire and East Yorkshire, connecting to the Atlantic via the Pentland Firth in the last glaciation (of over 300,000 years) is a condition for the relatively late cutting through of the Strait to the south.
File:Strait of Dover MODIS.jpg
A 2007 study concluded that the Strait was formed by erosion caused by two major floods.{{cite journal |last1 = Gupta |first1 = Sanjeev |last2 = Collier |first2 = Jenny S. |last3 = Palmer-Felgate |first3 = Andy |last4 = Potter |first4 = Graeme |title = Catastrophic Flooding Origin of Shelf Valley Systems in the English Channel |journal = Nature |volume = 448 |year = 2007 |doi = 10.1038/nature06018 |pmid = 17637667 |issue = 7151 |pages = 342–5 |bibcode = 2007Natur.448..342G |s2cid = 4408290 }}{{cite journal |title = Europe Cut Adrift |first = Philip |last = Gibbard |journal = Nature |volume = 448 |issue = 7151 |pages = 259–60 |date = 19 July 2007 |doi = 10.1038/448259a |pmid = 17637645 |bibcode = 2007Natur.448..259G |doi-access = free }} The first was about 425,000 years ago, when an ice-dammed lake in the southern North Sea overflowed and broke the Weald-Artois (Boulonnais) chalk range in a catastrophic erosion and flood event. Consequently the ice-age-muted flows from the Thames and Scheldt flowed through the gap into the English Channel/Inlet, but the Meuse and Rhine still flowed without any significant link to the inlet (such as today's IJssel distributary supports). In a second flood about 225,000 years ago supported by glaciers extending from areas then land such as the Zuiderzee, 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. A further update in 2017 attributed underwater holes in the Channel floor, "100 m deep" and in places "several kilometres in diameter", to lake water plunging over a rock ridge causing isolated depressions or plunge pools.{{cite news |url = https://www.bbc.co.uk/news/science-environment-39494740 |title = Evidence of Ancient 'Geological Brexit' Revealed |first = Rebecca |last = Morelle |author-link = Rebecca Morelle |work = BBC News:Science & Environment |date = 4 April 2017 |access-date = 6 April 2017 }}
The melting ice and rising sea levels submerged Doggerland, the area linking Britain to France, around 6,500–6,200 BCE.
The Lobourg strait, the deepest part the strait, runs its {{cvt|6|km|0|adj=on}}wide slash on a NNE–SSW axis. Nearer to the French coast than to the English, it borders the Varne sandbank (shoals) where it plunges to {{cvt|68|m}} and further south, the Ridge bank (shoals) (French name "Colbart") with a maximum depth of {{cvt|62|m}}.{{cite web |url = http://www.sea-seek.com/?geo=1354 |title = Pas de Calais – Dover Strait |website = sea-seek.com }}{{cite web |url = http://www.sussex.ac.uk/geography/researchprojects/coastview/Offshore/offshore.htm |title = CoastView – What happens offshore? |work = GEOSYNTH-Project |publisher = University of Sussex }}
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Marine wildlife
File:Dover AST 2001073 lrg.jpg Terra satellite image, March 2001]]
The depth of the strait varies between {{cvt|68|m}} at the Lobourg strait and {{cvt|20|m}} at the highest banks. The seabed forms successions of three habitats:
- rocky zones relatively deserted by ships wanting to spare their nets
- sandy flats
- sub-aqueous dunes.
The strong tidal currents of the strait at depth slow around its rocky masses as these stimulate countercurrents and deep, calm pockets where many species can find shelter.{{cite web |url = https://www.youtube.com/watch?v=vfTrDGK3j3w |title = Underwater video of the ridens |website = YouTube }} In these calmer lee zones, the water is clearer than in the rest of the strait; thus algae can grow despite the {{cvt|46|m}} average depth. They help increase diversity in the local species – some of which are endemic to the strait. Moreover, this is a transition zone for the species of the Atlantic Ocean and those of the southern part of the North Sea.
This mix of various environments promotes a wide variety of wildlife.{{cite journal |last1 = Davoult |first1 = D. |last2 = Richard |first2 = A. |title = Les Ridens, haut-fond rocheux isolé du Pas de Calais: un peuplement remarquable |trans-title = The Ridens, Rocky Shallows in the Center of the Channel: A Distinguished Settlement |journal = Cahiers de Biologie Marine |url = http://cat.inist.fr/?aModele=afficheN&cpsidt=7856448 |volume = 29 |date = 1988 |issue = 1 |pages = 93–107 |language = fr }}
The Ridens de Boulogne, a {{cvt|10|-|20|m}} deep rocky shoal, partially sand-capped,{{cvt|15|nmi}} west of Boulogne, boasts the highest profusion of maerl in the strait.{{cite web |language = fr |url = http://www.eptb-bresle.com/userfiles/files/PNM_%203estuaires_Vol1_richesses%20de%20la%20mer.pdf |title = Richesses de la mer |trans-title = Richness of the sea |publisher = Picardy Estuaries and Opal Sea Marine Natural Park }}
Thus some {{cvt|682|km2}} of the strait is classified as a Natura 2000 protection zone named Ridens et dunes hydrauliques du Pas de Calais (Ridens and sub-aqueous dunes of the Dover Strait). This includes the sub-aqueous dunes of Varne, Colbart, Vergoyer and Bassurelle, the Ridens de Boulogne, and the Lobourg channel which provides calmer and clearer waters due to its depth reaching {{cvt|68|m}}.{{cite web |url = http://inpn.mnhn.fr/site/natura2000/FR3102004 |title = Ridens et dunes hydrauliques du Pas de Calais |publisher = Natura 2000 |language = fr }}
Unusual crossings
{{Further|English Channel#History of Channel crossings}}
Many crossings other than in conventional vessels have been attempted, including by pedalo, jetpack, bathtub, amphibious vehicle and more commonly by swimming. Since French law bans many of them, unlike English law, most such crossings originate in England.{{citation needed|date=July 2017}}
Ice
In the late 17th century during the "Little Ice Age", there were reports of severe winter ice in the English Channel{{cite web|url=http://www.pastpresented.info/frost1683.htm|website=www.pastpresented.info|title=The Great Frost of 1683-4|access-date=20 March 2020}}{{cite journal |url=https://archive.org/details/sim_notes-and-queries_1861-03-16_11_272/page/218/mode/2up |title = Notes and Queries |journal=Notes and Queries |series = Second Series |volume = 11 |page = 219 |date = 16 March 1861 |via=archive.org}} and Strait of Dover, including a case in 1684 of only a league of open water remaining between Dover and Calais.{{cite book |url = https://archive.org/details/worldofwondersre00londrich/page/22/mode/2up |title = The World of Wonders: A Record of Things Wonderful in Nature, Science, and Art |location = London |publisher = Cassel Petter & Galpin |year = 1869 }}
See also
Notes
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References
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External links
- [http://www.mcga.gov.uk/c4mca/mcga07-home/emergencyresponse/mcga-searchandrescue/mcga-hmcgsar-sarsystem/channel_navigation_information_service__cnis_.htm Channel Navigation Information Service]
- [http://www.channelswimming.net Channel Swimming & Piloting Federation]
- [http://www.channelswimmingassociation.com Channel Swimming Association]
- [https://archive.today/20121208145804/http://mapserver.maptech.com/homepage/index.cfm?lat=50.9963257376773&lon=1.4719665462225308&scale=1500000&zoom=50&type=0&icon=0&width=498&height=498&searchscope=dom&CFID=1719760&CFTOKEN=33728793&scriptfile=http://mapserver.maptech.com/homepage/index.cfm&latlontype=DMS Depth Chart showing straits and former course of Rhine]
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Category:France–United Kingdom border
Category:International straits