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Millions of years ago, the Green River carved a path through the Uinta Mountains instead of flowing around the formation. Now, researchers have discovered how this could have happened.

The Green River originates in Wyoming and links up with the Colorado River in Canyonlands National Park in Utah. Around 8 million years ago, the Green River carved its way through the 13,000-foot-tall (4,000 meters) Uinta Mountains in northeastern Utah and northwestern Colorado instead of flowing around the formation. But in a new study, researchers argue this isn't possible without a mechanism to lower the mountains.

"It's such a weird path," study lead author Adam Smith, a researcher in numerical modeling at the University of Glasgow in the U.K., told Live Science. "We know from dating and other stuff that the mountain range is 50 million years old and the river has only been running that course since 8 million years ago, but possibly as soon as 2 million years ago."

Instead, the researchers behind the new study suggest the Uinta Mountains subsided to the point where the Green River could flow over them. The researchers propose that a phenomenon called a "lithospheric drip" tugged the mountains down before a rebound effect caused the landscape to rise upwards once more, resulting in the topography we see today.

The findings were published Monday (Feb. 2) in the Journal of Geophysical Research: Earth Surface.

Lithospheric drips are high-density regions that can form directly beneath mountains, where Earth's crust meets the top of the mantle — the layer of the planet between the crust and the outer core. The weight of the mountains increases the pressure at the base of the crust, forming minerals like garnet that are heavier than mantle rocks. Eventually, these minerals form a blob that drips from the base of the crust, dragging the mountains down and reducing their elevation at Earth's surface.

Lithospheric drips trigger a rebound effect when they finally detach and sink into the mantle. The concept of these drips is relatively recent, but evidence of them has been found in several places, including the Andes. "They can happen wherever you have had a mountain range form, and they can happen at any time," Smith said.

Instead, the researchers behind the new study suggest the Uinta Mountains subsided to the point where the Green River could flow over them. The researchers propose that a phenomenon called a "lithospheric drip" tugged the mountains down before a rebound effect caused the landscape to rise upwards once more, resulting in the topography we see today.

The findings were published Monday (Feb. 2) in the Journal of Geophysical Research: Earth Surface.

Lithospheric drips are high-density regions that can form directly beneath mountains, where Earth's crust meets the top of the mantle — the layer of the planet between the crust and the outer core. The weight of the mountains increases the pressure at the base of the crust, forming minerals like garnet that are heavier than mantle rocks. Eventually, these minerals form a blob that drips from the base of the crust, dragging the mountains down and reducing their elevation at Earth's surface.

Lithospheric drips trigger a rebound effect when they finally detach and sink into the mantle. The concept of these drips is relatively recent, but evidence of them has been found in several places, including the Andes. "They can happen wherever you have had a mountain range form, and they can happen at any time," Smith said.