The Green River's path through Utah makes no sense, geologically speaking. Instead of going around the towering Uinta Mountains—the much easier route—the river runs smack through the middle of the range before joining the Colorado River. "It's such a weird path," Adam Smith of the University of Glasgow tells LiveScience. The question of why the river took this route has long vexed the field, but a new study authored by Smith in the Journal of Geophysical Research: Earth Surface might finally have the answer.
In geology speak, this answer involves a phenomenon called "lithospheric drip." In layman's terms, it involves the "Earth's crust behaving a bit like soft wax," as IFL Science puts it. Under this theory, the mountain range temporarily subsided millions of years ago, before rebounding back to its current height. The Green River carved out its path somewhere between 2 million and 8 million years ago—evidently when the mountains were much lower than they are now. Popular Science lays it out:
- "This phenomenon begins when a dense layer of mineral-rich substances forms at the base of the crust. Over time, the layer grows heavy enough to sink into the mantle. When this happens, the descent can also tug on the land above it and even lower a mountain range like Uinta." Eventually this drip breaks off, and the land rebounds upward again.
It's more than mere guesswork. Smith's team combined seismic imaging—essentially a CT scan of the subsurface—with computer models of the river's network to support their theory. They identified a cold, circular mass about 120 miles below the surface, which they believe to be the "ancient, broken fragment of a drip" that gave the Green its path. The findings undercut rival explanations, including that the river was older than the mountains or that it spilled over a growing pile of sediment. Smith's team argues that lithospheric drips, still a relatively new idea in geology, may explain more oddities in the landscape than previously recognized.
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