The forces creating the opening of Gibraltar have also closed it. The Mediterranean is subject to large tectonic force in between the continents of Africa and Europe. Eventually the Strait of Gibraltar might close again and the Mediterranean would more and less dry up. These large forces create beauty with regular forms as can be found here:
The mathematics behind this are amazing. Note the diagonal tectonic feature from SW to NE, crossing the center of the WE-axis extending from the middle of Gibraltar Strait. And the two semicircles make the coastlines holistic and absolutely symmetric.
So should we try to explain this? The same story repeats itself very often, namely WE-alignement can be found at many locations. Tension like the pressure between Africa and Europe can then lead to elliptical forms or even circular. Many others have noted the shape of the surroundings of Gibraltar, suggesting for instance that this is due to meteor impact. Here it is suggested that the the interplay between symmetric convection rolls, aligned almost NS through Gibraltar, and the horizontal tectonic forces are responsible for this obvious regularity.
The Nile flows directly from south to north into the Mediterranean, and the Atlantic Ocean flows directly through this opening from west to east. Gradually we realize how the combination of Earth’s rotation and mantle convection shapes our surroundings.