Turkey - 博斯普魯斯海峽 Bosporus in Turkey

View of the entrance to the Bosporus from the Sea of Marmara, as seen from the Topkapı Palace

The Bosphorus or Bosporus, also known as the Istanbul Strait, is a strait that forms part of the boundary between Europe and Asia. It is one of the Turkish Straits, along with the Dardanelles. The world's narrowest strait used for international navigation, it connects the Black Sea with the Sea of Marmara (which is connected by the Dardanelles to the Aegean Sea, and thereby to the Mediterranean Sea).

Ottoman era waterfront houses on the Bosporus

Bosphorus' limits are defined as the connecting line between the lighthouses Rumeli Feneri and Anadolu Feneri in the north and between the Ahırkapı Feneri and the Kadıköy İnciburnu Feneri in the south.

Ottoman era waterfront houses on the Bosporus

 The strait is between the limits 31 km (17 nmi) long, with a width of 3,329 m (1.798 nmi) at the northern entrance and 2,826 m (1.526 nmi) at the southern entrance. Its maximum width is 3,420 m (1.85 nmi) between Umuryeri and Büyükdere Limanı, and minimum width 704 m (0.380 nmi) between Kandilli Point and Aşiyan.

Bosphorus Bridge.

The depth of Bosphorus varies from 36 to 124 m (118 to 407 ft) in midstream with an average of 65 m (213 ft). The deepest location is between Kandilli and Bebek with 110 m (360 ft). The most shallow locations are off Kadıköy İnciburnu on the northward route with 18 m (59 ft) and off Aşiyan Point on the southward route with 13 m (43 ft).

The Rumelihisarı on the Bosporus with both of bridges which span the strait.

The shores of the strait are heavily populated as the city of Istanbul (with a metropolitan area in excess of 11 million inhabitants) straddles it.

 

 View of the Bosphorus and Fatih Sultan Mehmet Bridge as seen from Rumelihisarı

The name comes from Greek Bosporos (Βόσπορος), which the ancient Greeks analysed as bous βοῦς 'ox' + poros πόρος 'means of passing a river, ford, ferry', thus meaning 'ox-ford'. Although it has been known for a while that the Black Sea and the Sea of Marmara flow into each other in an example of a density flow, findings of a study by the University of Leeds in August 2010 reveal that there is in fact an underwater river flowing through the Mediterranean and under the Bosphorus (caused by the difference in density of the two seas), which would be the sixth largest river on Earth if it were to be on land.

Formation

The exact cause for the formation of the Bosphorus remains the subject of vigorous debate among geologists. Thousands of years ago, the Black Sea became disconnected from the Aegean Sea.

A view of the Bosphorus strait, with the Fatih Sultan Mehmet Bridge seen in the background

The Black Sea deluge theory (published in 1997 by William Ryan and Walter Pitman from Columbia University) contends that the Bosphorus was formed about 5600 BC when the rising waters of the Mediterranean/Sea of Marmara breached through to the Black Sea, which at the time (according to the theory) was a low-lying body of fresh water.

Panoramic view of a portion of the Bosphorus, as seen from the Ulus neighbourhood on the European side, with the Fatih Sultan Mehmet Bridge at left and the Bosphorus Bridge at right.

It is also said in myth that floating rocks known as the Symplegades or Clashing Rocks once crushed any ship that attempted passage of the Bosporus until the hero Jason obtained passage, whereupon the rocks became fixed, and Greek access to the Black Sea was opened.

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