Strait of Dover

Lore & Background

The Strait of Dover was formed through scouring by erosion. For many millennia since the last warm interglacial, it had been a land bridge linking the Weald in Great Britain to the Boulonnais in Pas de Calais. At the height of the last ice age, the English Channel was almost entirely land. The predominant geology of both coasts and the seafloor is chalk, which has created the white cliffs of Dover and Cap Blanc Nez. The Channel Tunnel was bored through solid chalk, the compacted remains of sea creatures and marine-deposited calciferous rock debris.

A 2007 study by British geoscientists Sanjeev Gupta and Jenny Collier concluded that the strait was formed by erosion caused by two major floods. The first, about 425,000 years ago, occurred when an ice-dammed lake in the southern North Sea overflowed and broke the Weald-Artois chalk range. The second flood, about 225,000 years ago, involved the Meuse and Rhine being ice-dammed into a lake that broke catastrophically through a high weak barrier. Both floods cut massive flood channels in the dry bed of the English Channel. 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.

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 of the strait, runs a 6 km wide slash on a NNE–SSW axis, nearer to the French coast than to the English.

Reader's Guide

The Strait of Dover holds immense significance as the primary maritime gateway between the Atlantic Ocean and the North Sea and Baltic Sea. Most maritime traffic passes through this strait rather than taking the longer and more dangerous route around the north of Scotland. Its role as one of the busiest international seaways has made traffic safety a critical issue, with HM Coastguard and the Maritime Gendarmerie maintaining a 24-hour watch and enforcing strict shipping lanes. The strait is also crossed by ferries linking Dover to Calais and Dunkirk, and since 1994 the Channel Tunnel has provided an alternative route beneath the seabed.

Geologically, the strait's formation through catastrophic floods has shaped the English Channel and influenced the region's ecology. The strong tidal currents and varied seabed habitats—rocky zones, sandy flats, and sub-aqueous dunes—support a wide variety of marine wildlife, including endemic species. The Ridens de Boulogne, a rocky shoal west of Boulogne, boasts the highest profusion of maerl in the strait. The area is classified as a Natura 2000 protection zone.

Culturally, the strait is famous for cross-channel swimming, with the route between South Foreland and Cap Gris-Nez being the most popular. On a clear day, the opposite coastline is visible with the naked eye, notably the White Cliffs of Dover from France. The strait has also been the site of unusual crossings, including by pedalo, jetpack, bathtub, and amphibious vehicle. During the Little Ice Age in the late 17th century, severe winter ice was reported, including a case in 1684 of only a league of open water remaining between Dover and Calais.

Did You Know?

• The shortest distance across the Strait of Dover is 20.6 miles (33.2 km), from South Foreland to Cap Gris-Nez.
• The strait is one of the busiest international seaways, used by over 400 commercial vessels daily.
• The strait was formed by two major catastrophic floods, the first about 425,000 years ago and the second about 225,000 years ago.
• During the Little Ice Age in 1684, only a league of open water remained between Dover and Calais due to severe ice.