On land, most canyons are carved by erosion from rivers over millions of years. In the ocean, things are a bit trickier. The King’s Trough Complex, located more than 600 miles off the coast of Portugal, is a massive canyon that includes one of the deepest points in the Atlantic Ocean—and was once a candidate to become an underwater nuclear waste dumping spot. But how did it get there?
To find out, geologists from GEOMAR Helmholtz Centre for Ocean Research Kiel in Germany hit the seas in a 300-foot research vessel equipped with high-resolution sonar systems to map the ocean floor and a chain bag dredge to retrieve rock samples. After analyzing the chemical composition of the volcanic rocks, the team was able to determine how and when this deep-sea canyon formed. They published their findings in Geochemistry, Geophysics, Geosystems (G-Cubed).
“Researchers have long suspected that tectonic processes—that is, movements of the Earth’s crust—played a central role in the formation of the King’s Trough,” study author Antje Dürkefälden explained in a statement. “Our results now explain for the first time why this remarkable structure developed precisely at this location.”
Between 37 and 24 million years ago, a tectonic plate boundary shifted to the area, resulting in the crust fracturing and the seafloor between Europe and Africa opening like a zipper in an east-west direction. Prior to the shift, the crust was thickened and heated by an upwelling of molten rock from the mantle, making it particularly fragile.
Read more: “Why Is It So Difficult to Map the Ocean?”
“This thickened, heated crust may have made the region mechanically weaker, so that the plate boundary preferentially shifted here,” added co-author Jörg Geldmacher. “When the plate boundary later moved farther south toward the modern Azores, the formation of the King’s Trough also came to a halt.”
It’s a remarkable example of how activity deep within our planet’s molten mantle can have a dramatic impact on the surface. 
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Lead image: Dürkefälden, A., et al. Geochemistry, Geophysics, Geosystems (2025).
