It is located off the coast of Portugal, like a long scar on the ocean floor which extends over nearly 500 km, longer than the American Grand Canyon (446 km). “ King’s Trough », from its little name, is not really a cayon in the geological sense of the term, but a complex of dizzying pits plunging up to 4,500 meters deepdiscovered in 1951 by the British research vessel Discovery II.
It has therefore been listed for a long time, but never we did not understand the exact circumstances of its formation. Fortunately, an international team led by the GEOMAR (Helmholtz Centre for Ocean Research Kiel) went on an expedition in 2020 to unravel this mystery by taking basalt samples from the walls of the pit. This dive into the abyss revealed its true nature and was the subject of a publication in November 2025 in the journal Geochemistry, Geophysics, Geosystems.
The effect “ zipper »: the earth’s crust is cracking
IF the Grand Canyon was carved over millions of years by river erosion, King’s Trough East born from a tectonic episode that occurred 37 to 24 million years ago (Oligocene period). At that time, the boundary between the African and European plates was not where we know it today, but crossed right through the North Atlantic.
It was formed by tearing of the ocean floor, which spread from east to west. « Our results finally explain why this extraordinary structure took root precisely at this location. », deciphers Antje Dürkefälden, lead author of the study. A slow process, like a “ zipper » which we would gently unzip.
This rupture was caused by what is called the pushing to wrinkle (or « ridge push “); During the Oligocene, the Atlantic Ocean was in full expansion. In its middle, the mid-Atlantic ridge was constantly producing new earth crust, which pushed the African and European continents outwards.
As the boundary between the two plates, King’s Troughmeandered, under the pressure of oceanic expansion, the Eurasian plate gave way where it was most vulnerable. At the eastern edge of the formation, where this process began most violently, we find today Peake Deep. A true endless hole plunging more than 6,000 meters, it can be considered the epicenter of this old earthquake.an open wound in the basalt that has never closed since.
A crust preheated by the bowels of the Earth
But why, in this case, did the earth’s crust crack in this place? After all, there are thousands of kilometers of plate boundaries where such a scar could have emerged. According to GEOMAR researchers, well before the plates began to move apart, an upwelling of very voluminous mantle (composed mainly of peridotite, a very dense rock) had already “prepared the ground” by heating the oceanic crust from below.
A thermal flow which thickened the rock, as if it passed under a gigantic blowtorch, which also made it more malleable and less conducive to uniting against tectonic thrusts. “ This thickened and heated crust may have made the region mechanically weaker, so that the plate boundary moved here preferentially », explains Jörg Geldmacher, co-author of the study.
The scar has finished spread now 24 million years agowhen the boundary between the Eurasian and African plates shifted further south to give birth to the current Azores archipelago. Moreover, an almost identical process is taking place right now under these islands (Terceira Rift), since this structure has been tearing apart for 1 million years. The area will probably become, in a few million years, an abyssal pit as deep as King’s Trough : the Azores will not disappear, in fact the opposite is true. If the ocean floor collapses all around to form a trench, the islands will continue to grow thanks to the contribution of volcanic material from the depths.
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