The Strait of Gibraltar, also called the Straits of Gibraltar, is a narrow waterway that links the Atlantic Ocean to the Mediterranean Sea and divides Europe from Africa. The closest distance between the two continents at the narrowest part of the strait is 7.7 nautical miles (14.2 kilometers, 8.9 statute miles). Ferries travel between Europe and Africa daily, with trips taking as little as 35 minutes. The depth of the strait varies from 300 to 900 meters (980 to 2,950 feet; 160 to 490 fathoms).

The strait is located within the territorial waters of Morocco, Spain, and the British overseas territory of Gibraltar. According to the United Nations Convention on the Law of the Sea, foreign ships and aircraft are allowed to pass through the strait of Gibraltar if they are traveling continuously without stopping.

Names and etymology

The name Gibraltar comes from the Rock of Gibraltar, which is named after the Arabic phrase Jabal Ṭāriq, meaning "Tariq's Mount." This name honors Tariq ibn Ziyad. The area is also called the Straits of Gibraltar, the Gut of Gibraltar (a term now rarely used), and STROG (STRait Of Gibraltar) in naval contexts.

Another Arabic name for the area is Bāb al-maghrib, which translates to "Gate of the West" or "Gate of the sunset," and also refers to "Gate of the Maghreb" or "Gate of Morocco." In the Middle Ages, it was sometimes called Az-Zuqāq, meaning "the Passage," or bḥar az-zuqāq, meaning "the passage sea." The Romans called it Fretum Gaditanum, or "Strait of Cádiz."

In Latin, the strait was known as Fretum Herculeum, based on the ancient Greek term "Pillars of Hercules" (Ancient Greek: αἱ Ἡράκλειοι στῆλαι). This name refers to the mountains, such as Gibraltar, that stand on either side of the strait.

Location

On the northern side of the Strait of Gibraltar are Spain and Gibraltar, which is a British territory in the Iberian Peninsula. On the southern side are Morocco and Ceuta, which is a city in northern Africa that is part of Spain.

Because of its location, the Strait is often used for illegal immigration from Africa to Europe.

The International Hydrographic Organization sets the boundaries of the Strait of Gibraltar as follows:

Geology

The seabed of the Strait is made up of layers of clay and rock called Betic-Rif flysch, covered by sediments from the Pliocene and Quaternary periods. These sediments are made of calcium carbonate and come from cold water coral communities. Exposed rock surfaces, large grains of sand, and nearby sand dunes show that strong underwater currents exist today.

About 5.97 million years ago, the connection between the Mediterranean Sea and the Atlantic Ocean through the Betic and Rifan Corridor gradually closed. This caused the Mediterranean Sea’s salt levels to rise repeatedly, leading to the buildup of salt and gypsum deposits during the Messinian salinity crisis. In this environment, high mineral concentrations, warm temperatures, and still water currents caused salt and other minerals to form layers on the seabed. Large salt and mineral deposits across the Mediterranean basin are linked to this time. Scientists believe this process lasted about 640,000 years, which is a short time in geological history.

If the Strait were closed today at the current higher sea level, most of the water in the Mediterranean Sea would likely evaporate within 1,000 years, similar to what happened in the past. This would leave behind salt deposits like those found under the seafloor today.

After a long period of limited or no water flow between the Atlantic Ocean and the Mediterranean Sea, around 5.33 million years ago, the connection was fully restored through the Strait of Gibraltar by a flood called the Zanclean flood. This event kept the Strait open ever since. Water erosion from the Atlantic Ocean is believed to have created the Strait’s current depth, which is about 900 meters (3,000 feet) at the narrowest point and 280 meters (920 feet) at the Camarinal Sill. The Strait may close again in the future as the African Plate moves northward relative to the Eurasian Plate, but this will happen over very long geological timescales, not within human lifetimes.

Biodiversity

The Strait has been recognized as an Important Bird Area by BirdLife International due to the large number of seabirds that pass through it each year while traveling between the Mediterranean and the Atlantic. These birds include many Scopoli's and Balearic shearwaters, Audouin's and lesser black-backed gulls, razorbills, and Atlantic puffins.

A group of about 36 orcas lives near the Strait, one of the few such groups remaining in Western European waters. This pod may become extinct in the future because of the long-term effects of PCB pollution.

History

Evidence shows that Neanderthals first lived in the area around 125,000 years ago. The Rock of Gibraltar may have been one of the last places where Neanderthals lived, with signs of their presence there as recently as 24,000 years ago. Archaeological findings also show that modern humans, called Homo sapiens, lived in the area about 40,000 years ago.

The short distance between the two sides of the Strait of Gibraltar has made it an important crossing point for many groups and civilizations throughout history. These include Carthaginians fighting against Rome, Romans traveling between the regions of Hispania and Mauritania, Vandals attacking from Germania through Western Rome into North Africa in the 5th century, Moors and Berbers in the 8th–11th centuries, and Spain and Portugal in the 16th century.

Starting in 1492, the Strait began to act as a barrier that limited the movement of people, ideas, and languages between the two sides. That year, the last Muslim government north of the Strait was defeated by Spanish forces. After this, the Strait helped create two very different cultures on either side, even though they had shared a similar culture for more than 500 years from the 8th century to the early 13th century.

On the northern side, Christian-European culture and the Romance Spanish language have been dominant since the removal of the last Muslim kingdom in 1492. On the southern side, Muslim-Arabic/Mediterranean culture and the Arabic language have been dominant since the spread of Islam into North Africa in the 700s.

The small British area of Gibraltar represents a third cultural group in the region. This area was given to Britain forever in the Peace of Utrecht. Since then, Gibraltar has been used by the United Kingdom to control the sea routes into and out of the Mediterranean.

After the Spanish coup in July 1936, the Spanish Republican Navy tried to stop the movement of Army of Africa troops from Spanish Morocco to Peninsular Spain. On August 5, 1936, the Convoy de la Victoria successfully transported at least 2,500 soldiers across the Strait, breaking the Republican blockade.

Communications

The Strait of Gibraltar is an important path for ships traveling between the Mediterranean Sea and the Atlantic Ocean. Ferries travel across the Strait between Spain and Morocco, as well as between Spain and Ceuta, and between Gibraltar and Tangier. Some people have suggested building a bridge or tunnel across the Strait of Gibraltar.

In the 1980s, Spain and Morocco began discussing the idea of building a tunnel under the Strait. In December 2003, both countries agreed to study the construction of an undersea rail tunnel to connect their train systems across the Strait. The train tracks would be 1,435 mm (4 feet 8 and 1/2 inches) wide to match the planned changes to parts of the existing train system. While the project remained in the planning stage, Spanish and Moroccan officials met occasionally to discuss it, including in 2012. Those talks did not lead to any progress, but in April 2021, ministers from both countries agreed to hold a joint meeting in Casablanca to restart discussions about the tunnel. Earlier, in January 2021, the UK government studied plans for a tunnel to connect Gibraltar with Tangier, which would replace the earlier Spanish-Moroccan project that had not produced results after more than 40 years of talks.

Special flow and wave patterns

The Strait of Gibraltar connects the Atlantic Ocean directly to the Mediterranean Sea. This connection creates special water movement and wave patterns. These patterns form because of the interaction of local and global evaporation, water temperatures, tides, and wind.

Water moves continuously through the Strait in both eastward and westward directions. A smaller amount of deep, salty, and dense water flows westward (called the Mediterranean outflow), while a larger amount of less salty and less dense surface water flows eastward (called the Mediterranean inflow). These general movements can sometimes be briefly interrupted by temporary tidal flows, depending on the positions of the moon and sun. The overall flow is eastward because the rate of evaporation in the Mediterranean is greater than the total amount of water entering from rivers and rainfall. At the western end of the Strait is the Camarinal Sill, the shallowest point, which limits mixing between the colder, less salty Atlantic water and the warmer, saltier Mediterranean water.

Mediterranean water is much saltier than Atlantic water, so it sinks below the incoming water and forms a highly saline layer of deep water. This layer moves out into the Atlantic as the Mediterranean outflow. On the Atlantic side of the Strait, a density boundary separates the Mediterranean outflow from other waters at about 100 meters (330 feet) deep. These waters flow out along the continental slope, losing salinity until they mix more quickly at a depth of about 1,000 meters (3,300 feet). The Mediterranean outflow can be traced thousands of kilometers west of the Strait before losing its distinct identity.

During World War II, German submarines used the currents to enter the Mediterranean undetected by keeping their engines off. From September 1941 to May 1944, Germany sent 62 submarines into the Mediterranean. These submarines had to pass through the British-controlled Strait of Gibraltar, where nine were sunk and ten more had to turn back due to damage.

Internal waves (waves at the density boundary layer) often form in the Strait. Like traffic merging on a highway, water flow is restricted in both directions because it must pass over the Camarinal Sill. When large tidal flows enter the Strait and the high tide ends, internal waves form at the Camarinal Sill and move eastward. These waves can occur at great depths and are sometimes barely visible at the surface or clearly visible in satellite images. They continue moving eastward and bend around coastal features. These waves can sometimes be seen for up to 100 kilometers (62 miles) and may create patterns with other waves.

Territorial waters

The Strait of Gibraltar, except for its far eastern end, is located within the territorial waters of Spain and Morocco. The United Kingdom claims control over 3 nautical miles (5.6 km; 3.5 mi) of the northern side of the Strait near Gibraltar. This claim means that part of the Strait is within British territorial waters. However, because this distance is less than the maximum 12 nautical miles (22 km; 14 mi) allowed by international law, the area beyond Britain’s claim is considered international waters. Spain disputes the United Kingdom’s ownership of Gibraltar and its surrounding waters. Similarly, Morocco disputes Spain’s control over Ceuta, a city on the southern coast of the Strait. There are also small islands, such as the disputed Isla Perejil, which are claimed by both Morocco and Spain.

According to the United Nations Convention on the Law of the Sea, ships and aircraft passing through the Strait of Gibraltar are allowed to do so under a special rule called "transit passage." This rule gives vessels and planes more freedom to travel through the Strait compared to the more restricted "innocent passage" allowed in most territorial waters. This means that ships and planes can freely navigate or fly over the Strait of Gibraltar for the purpose of crossing it.

Power generation

Some studies have suggested building tidal power stations in the Strait, using the steady water flow there to create electricity.

In the 1920s and 1930s, the Atlantropa project planned to build a dam across the Strait to produce a large amount of electricity and lower the Mediterranean Sea’s level by hundreds of meters. This would create new land for people to live on. However, this plan could harm the local climate and environment and change how strong the West African Monsoon is.

History of Strait crossings

Some people have crossed the Strait of Gibraltar by swimming, using a powered paraglider, and riding a stand-up paddleboard.

Mercedes Gleitze was the first person known to swim across the Strait of Gibraltar on April 6, 1928. It took her 12 hours and 50 minutes to complete the journey. This was her sixth try to swim the Strait, and her first attempt was in December 1927.

Francesco Stipo was the first person known to cross the Strait of Gibraltar using a powered paraglider on July 11, 1995.

According to the Spanish newspaper Europa Sur, Stipo flew from Tarifa to Ceuta in less than one hour. He was followed by the Red Cross boat Salvamar Tarifa and landed near the Port of Ceuta.

Chris Ziaja and Nik Benner were the first people known to cross the Strait of Gibraltar using a stand-up paddleboard on October 4, 2010. They started from Punta Carnero and reached Ceuta after four and a half hours.