8 October 2025

A year ago on a birding trip at the Strait of Gibraltar we stopped at the Torre del Guadelmesi a watchtower on the Spanish coast. Below us in the Mediterranean was an odd formation of parallel rocks called flysch.

Flysch is a sequence of sedimentary rock layers that progress from deep-water and turbidity flow deposits to shallow-water shales and sandstones. It is deposited when a deep basin forms rapidly on the continental side of a mountain building episode.

— Wikipedia: definition of Flysch

Here are two more examples near Tarifa, Spain.

The layers erode at different rates so the formation looks striped. If it was not so eroded the rocks could look like this formation in Basque Country, northern Spain.

What fascinated me was not the rock layers but the fact that they were tilted up, proving the relentless power of plate tectonics at the Strait. This animation shows how the horizontal layers became vertical.

The Strait of Gibraltar is on the tectonic plate boundary where the African plate has been pushing into and under — subducting — the Eurasian plate.

The Eurasian and African plates are moving in generally the same direction but you can see on the map below that the African plate is moving a little faster so it is ramming into Spain.

Geologists say that plate movement at the Mediterranean is complex and it has stalled so the plates may be changing places.

The continents are converging; and for many millions of years, the northern edge of the African tectonic plate has descended under Europe.

But this process has stalled; and at the European Geosciences Union (EGU) meeting last week [April 2011], scientists said we may be seeing Europe taking a turn.

If they are correct, this would signal the start of a new subduction zone – a rare event, scientifically fascinating.

“It looks possible that on the appropriate timescale, we are witnessing the beginning of subduction of Europe under Africa,” he told BBC News.

— BBC: Europe’s future lies under Africa, scientists suggest. 11 April 2011

When (or if) this happens, tilted rocks will rise on the African side of the Mediterranean. It will happen relentlessly but very very slowly. None of us will be around to see it.