There’s an interesting article at the BBC’s website about discussions between Spain and Morocco to build a tunnel across the Medeterranean
The Moroccan government has been holding talks with its Spanish counterparts to start the project, which would consist of a railway beneath the Strait of Gibraltar carrying freight, passengers and cars.
Work is expected to start in 2008.(…)
If that is the case, Africa and Europe, which split apart millions of years ago, could soon be joined together again permanently via a tunnel.
As the article points out, the engineering challenges that would be faced in building a tunnel to Africa are very different from those that arose during design and construction of the Chunnel”
There are a lot of challenges. First of all the sea at this point is 300m (1,000ft) deep – about five to six times deeper than the Channel Tunnel [linking the UK and France].
“Then there is the geological conditions. There are quite a lot of tectonic movements between the African and the European plates. So there would be quite a lot of movements in the earth, of stresses and so on.”
Here’s a picture of what the tunnel might look like when completed:
One of the challenges would be making sure all the signs leading toward the European side were in the right language, Arabic, so that the invading forces would know which exit to take as they arrived.