The Strait of Gibraltar (Arabic: مضيق جبل طارق, Spanish: Estrecho de Gibraltar) is a narrow strait that connects the Atlantic Ocean to the Mediterranean Sea and separates Spain in Europe from Morocco in Africa. The name comes from Gibraltar, which in turn originates from the Arabic Jebel Tariq (meaning "Tariq's mountain"), albeit the Arab name for the Strait is Bab el-Zakat or "Gate of Charity". It is also erroneously known as the Straits of Gibraltar, or STROG (Strait Of Gibraltar), in naval use and as "Pillars of Hercules" (Greek: Ηράκλειες Στήλες) in the ancient world.
Europe and Africa are separated by 7.7 nautical miles (14.24 km) of ocean at the strait's narrowest point. The Strait's depth ranges between 300 and 900 metres (980 and 3,000 ft) which possibly interacted with the lower mean sea level of the last major glaciation 20,000 years before present when the level of the sea was believed to be 110 to 120 metres (361 to 394 ft) lower. Ferries cross between the two continents every day in as little as 35 minutes. The Spanish side of the Strait is protected under El Estrecho Natural Park.
On the northern side of the Strait is Spain and Gibraltar (a British exclave in the Iberian Peninsula), while on the southern side is Morocco and Ceuta (a Spanish exclave in North Africa). Its boundaries were known in antiquity as the Pillars of Hercules. There are several islets, such as the disputed Isla Perejil, that are claimed by both Morocco and Spain.
Due to its location, the Strait is widely used for illegal immigration from Africa to Europe.
The International Hydrographic Organization defines the limits of the Strait of Gibraltar as follows:
On the West. A line joining Cape Trafalgar to Cape Spartel.
On the East. A line joining Europa Point to P. Almina (). </blockquote>
Around 5.9 million years ago, the connection between the Mediterranean Sea and the Atlantic Ocean along the Bethic and Rifan Corridor was progressively restricted until its total closure, effectively causing the salinity of the Mediterranean to periodically fall within the gypsum and salt deposition range, during what is known as the Messinian Salinity Crisis. In this water chemistry environment, dissolved mineral concentrations, temperature and stilled water currents combined properly and occurred regularly to precipitate many mineral salts in sea floor bedded layers. The resultant accumulation of various huge salt and mineral deposits about the Mediterranean basin are directly linked to this era. It is not believed this process took a long time geologically, lasting only 500-600 thousand-years, for it is further estimated that were the straits closed even at today's higher sea level, most water in the Mediterranean basin would evaporate within only a thousand years; as it is believed to have done then, and such an event would lay down similar mineral deposits as those such as the fabulous salt mines now found under the sea floor off Sicily. After a lengthy period of restricted intermittent or no water exchange between the Atlantic Ocean and Mediterranean basin, approximately 5.33 million years ago, the Atlantic-Mediterranean connection was completely reestablished through the Strait of Gibraltar, and has remained open ever since. It is expected that the strait will close again as the African Plate moves northward relative to the Eurasian Plate, but on geological rather than human timescales.
(For full articles on the history of the North Gibraltar shore, see History of Gibraltar or History of Spain, for the full article on the history of the south Gibraltar shore, see History of Morocco.)
Evidence of the first human habitation of the area by Neanderthals dates back to 125,000 years ago. In fact, it is believed that the Rock of Gibraltar may have been one of the last outposts of Neanderthal habitation in the world, with evidence of their presence there dating to as recently as only 24,000 years ago.
Archaeological evidence of Homo sapien habitation of the area dates back to ca. 40,000 years ago. Beginning in 1492, the straits began to play a certain cultural role in acting as a barrier against cross-strait conquest, and the flow of culture and language that would naturally follow such a conquest. In that year, the last Muslim government north of the straits was overthrown by a Spanish force. Since that time, the straits have come to foster the development two very distinct and varied cultures on either side of the straits. On the northern side of the straits, the Christian/ European culture has remained dominant(as it used to be in the sothern side too), along with the Latin based Spanish language, while on the southern side of the straits, the markedly different Muslim-arabic/ mediterranean culture came to dominate later, along with the Arabic language. For the last 5 centuries, the religious cultural intolerance more than the small travel barrier that the straits present, has come to act as a powerful enforcing agent of the cultural separation that exists between these two groups.
The small British enclave of the city of Gibraltar presents a third cultural group found in the straits. This enclave was first established in 1704, and has since been used by Britain to act as a surety for control of the sea lanes into and out of the Mediterranean.
The Strait is an important shipping route from the Mediterranean to the Atlantic. There are ferries that operate between Spain and Morocco across the strait, as well as between Spain and Ceuta and Gibraltar to Tangier.
Tunnel across the strait
In December 2003, Spain and Morocco agreed to explore the construction of an undersea rail tunnel to connect their rail systems across the Strait. The gauge of the rail would be 1,435 mm (4 ft 8.5 in) to match the proposed construction and conversion of significant parts of the existing broad gauge system to standard gauge.
Special flow and wave patterns
The Strait of Gibraltar serves to directly link the two largest otherwise separate bodies of water in the world. As such, this direct linkage creates certain unique flow and wave patterns. These unique patterns are created due to the interaction of various regional and global evaporative forces, tidal forces, and wind forces.
Inflow and outflow
Through the strait, water generally flows more or less continually in both an eastward and a westward direction. A smaller amount of deeper saltier and therefore denser waters continually work their way westwards (the Mediterranean outflow), while a larger amount of surface waters with lower salinity and density continually work their way eastwards (the Mediterranean inflow). These general flow tendencies may be occasionally interrupted for brief periods to accommodate temporary tidal flow requirements, depending on various lunar and solar alignments. Still, on the whole and over time, the balance of the water flow is eastwards, due to an evaporation rate within the Mediterranean basin higher than the combined inflow of all the rivers that empty into it. The shallow Camarinal Sill of the Strait of Gibraltar, which forms the shallowest point within the strait, acts to limit mixing between the cold, less saline Atlantic water and the warm Mediterranean waters. The Camarinal Sill is located at the far western end of the straits.
The Mediterranean waters are so much saltier than the Atlantic waters, that they sink below the constantly incoming water and form a highly saline (thermohaline, both warm and salty) layer of bottom water. This layer of bottom-water constantly works its way out into the Atlantic as the Mediterranean outflow. On the Atlantic side of the strait, a density boundary separates the Mediterranean outflow waters from the rest at about 100 metres (330 ft) depth. These waters flow out and down the continental slope, losing salinity, until they begin to mix and equilibrate more rapidly, much further out at a depth of about 1,000 metres (3,300 ft). The Mediterranean outflow water layer can be traced for thousands of kilometres west of the strait, before completely losing its identity.
During the Second World War German U-boats used the currents to pass in and out of the Mediterranean Sea without detection, by maintaining silence with engines off.
Internal waves (waves at the density boundary layer) are often produced by the strait. Like traffic merging on a highway, the water flow is constricted in both directions because it must pass over a shallow submarine barrier, the Camarinal Sill. When large tidal flows enter the Strait and the high tide relaxes, internal waves are generated at the Camarinal Sill and proceed eastwards. Even though the waves may occur down to great depths, occasionally at the surface the waves are almost imperceptible, at other times they can be seen clearly using satellite imagery. These internal waves continue to flow eastward and to refract around coastal features. They can sometimes be traced for as much as 100 kilometres (62 mi), and sometimes create interference patterns with refracted waves.
Some studies have proposed the possibility of erecting tidal power generating stations within the straits, to be powered from the predictable flow of current at the straits.
- List of straits
- Mediterranean Basin
- Strait of Gibraltar crossing
References and notes
- Climate Control Requires a Dam at the Strait of Gibraltar — American Geophysical Union, 1997. Accessed 26 February 2006. Gone 12 February 2010. Dam design at http://www.agu.org/sci_soc/eosrjohnsonf3.gif Building the dam and letting the Mediterranean Sea completely evaporate would raise Sea Level 15 meters over 1,000 years. Evaporating the first 100 meters or so would raise Sea Level 1 meter in about 100 years.
- Project for a Europe-Africa permanent link through the Strait of Gibraltar — United Nations Economic and Social Council, 2001. Accessed 26 February 2006.
- Map of Morocco — Multimap.com, 2006. Accessed 26 February 2006.
- (Spanish) Estudios Geográficos del Estrecho de Gibraltar — La Universidad de Tetuán and La Universidad de Sevilla. Accessed 26 February 2006.