Giant Sunken Island Revealed off Scotland

Prehistoric "Atlantis" found a mile deep—complete with peaks and riverbeds.

More than a mile (1.6 kilometers) under the North Atlantic, a sort of prehistoric Atlantis—complete with mountains and riverbeds—is coming into focus.

Millions of years ago, the giant island rode a pulse of volcanic energy to the surface before disappearing beneath the waves in the blink of an eye, geologically speaking, a new study says.

A few hundred miles west of Scotland's Orkney archipelago (map), the newfound island sank about 56 million years ago. It was first spotted in the early 2000s via reflection seismology data—a sonar-like technology—from oil-prospecting ships.

Scientists recently returned to the site to conduct a more detailed mapping study. Their results reveal that the drowned island once occupied an area of nearly 4,000 square miles (10,000 square kilometers)—which would have made it a little bigger than Puerto Rico (map).

"Hot Pulse" Blasted Island to Surface

The unique profile of one of the rivers imaged during the survey—which meandered more than 62 miles (100 kilometers) across the landscape and was fed by several tributaries—provides a powerful clue about how the island initially formed and why it eventually sank.

The river "had three flat portions, with steeper bits connecting them, resembling a staircase," explained study team member Ross Hartley, an earth scientist at the University of Cambridge.

The stepped contours suggest the island rose above the sea in three main phases over the course of several million years, the team says.

The rapid uplift was likely fueled by a plume of heated mantle from Earth's interior, they add. This "hot pulse" would have pushed part of the ocean bottom upward, raising some of it above sea level.

What Kinds of Creatures Ruled Ex-Island?

The lost land appears to have had a relatively short time in the sun, thanks to a cooling of Earth's crust and upper mantle, which dunked the island beneath the sea once again.

"It probably took one to two million years for the exposed surface to be submerged below sea level again," Hartley said. "That's a very short period of time on a geologic timescale." (Explore our prehistoric time line.)

It's unclear what kind of creatures might have lived on the island, though scientists say it formed about 10 million years after the extinction of the dinosaurs and about 55 million years before the appearance of humans.

Other studies have found fossil evidence of a few species of plants and microscopic marine organisms on the island, Hartley said. But so far "no evidence of larger animals has been found."

The sunken-island study appears in the current issue of the journal Nature Geoscience.