The Green River winds a surprisingly direct route through Utah’s Uinta Mountains. This river has carved a deep canyon straight through one of the mountains. This scenic setting has long puzzled geologists, who have wondered how the river punched through these ancient peaks. Now, researchers writing in the Journal of Geophysical Research: Earth Surface have found an answer.
The team says an unusual geological phenomenon that causes towering mountains to flatten and then rebound over millions of years explains the Green River’s path.
Read More: Sinkites Are Strange Bodies of Sand Beneath the Sea, and They’re Breaking the Laws of Geology
Why the Green River is So Significant
The Green River has an important place in American natural history.
“The merging of the Green and Colorado Rivers millions of years ago altered the continental divide of North America. It created the line that separates the rivers that flow into the Pacific from those that flow into the Atlantic, and created new habitat boundaries for wildlife that influenced their evolution. It's an enormously significant area of the continent,” said Adam Smith, an earth scientist at the University of Glasgow and study coauthor, in a statement.
The merging of the two rivers has confused geologists, as the Uinta Mountains, which are 50 million years old, are far older than the Green River’s current route, which is only about 8 million years old. Nonetheless, the river cuts a path straight through the mountains, including through the iconic Canyon of Lodore, to reach the Colorado River.
The area isn’t tectonically active, and Smith and his team had to reach for a concept still relatively new to the field to explain it. The team believes the river’s path was permitted by a process called lithospheric drip.
The Green River Flowing Through the Uinta Mountains
This process begins at the base of Earth’s crust, where dense mineral deposits begin to sink into the mantle. The land above this region of the crust then begins to collapse into the earth.
Eventually, researchers believe the mineral-dense “drip” severs from the land above, causing the mountain range to rebound, like a weighed-down clothesline when you quickly unpeg your laundry. This happens over millions of years, but leaves a characteristic mark: a bullseye-patterned uplift zone in the land sitting over the drip.
Smith and his colleagues believe the Green River sailed through the Uinta Mountains while they were dragged down by a lithospheric drip. The river eroded the rock and merged with the Colorado River during this time.
The team discovered the drip using seismic imaging, a technique like a geological CT scan that helps researchers image below Earth’s surface by analyzing how seismic waves pass through it. The team identified a round mass roughly 200 km (about 124 miles) below the Uinta Mountains. This is likely to be the broken-off section of the drip that dragged the mountains into the crust many years ago.
Finding the Bullseye
The team estimated that the bottom section of the drip sheared off between 2 million and 5 million years ago, roughly the same time the Green River passed through the mountains.
Modeling of nearby river networks detected the bullseye pattern that signifies the mountains rebound after separating from the lower drip. Smith said his team’s work discounted several rival theories as to how the river found its way through the mountains.
“The evidence we've collected strongly contradicts the idea that the river predated the mountains, or that sediment deposits might have built up enough for the river to overtop the range, or that erosion from the south of the mountains captured the Green River,” he said.
"We hope that this paper will help resolve a longstanding debate about one of North America's most significant river systems, and help build the growing body of evidence that lithospheric drips may be the hidden answer to more tectonic mysteries than we've previously realized."
Read More: Hidden Underwater Volcanoes May Explain Half of Earth’s Triassic Extinctions
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
- This article references information from a recent study published in the Journal of Geophysical Research: Earth Surface: A Lithospheric Drip Triggered Green and Colorado River Integration
