Flysch in the Mediterranean at Torre del Guadelmesi, Andalusia, Spain, 12 Sept 2024 (photo by Kate St. John)

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.

Here are two more examples near Tarifa, Spain.

Flysch at Parque Natural del Estrecho at the Strait of Gibraltar, Spain (from Wikimedia Commons)

Flysch at Parque Natural del Estrecho near the port of Tarifa, Spain (from Wikimedia Commons)

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.

Flysch outcropping at Playa de Itzurun, Basque Country, Spain (photo from Wikimedia Commons)

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.

Animated image of mountain formation by reverse fault (from Wikimedia Commons)

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

Map of Mediterranean tectonic plate boundaries (from Wikimedia Commons)

The Eurasian and African plates are moving in (sort of) 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.

Tectonic plates boundary types & movement from Wikimedia Commons

Geologists say that plate movement at the Mediterranean is complex and 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, 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.

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