Green River's apparent uphill route explained by lithospheric drip

Researchers reporting in the Journal of Geophysical Research: Earth Surface used seismic imaging and modeling to argue that a lithospheric drip lowered the Uinta Mountains 2–5 million years ago, enabling the Green River to cut a deep canyon and join the Colorado River.

New research proposes a geological process that explains how the Green River cut through the Uinta Mountains. The river's modern route is much younger than the mountains, and that timing has left scientists debating how the river reached the Colorado system. A team led by Adam Smith at the University of Glasgow published a study in the Journal of Geophysical Research: Earth Surface reporting seismic imaging and data modeling results. They report that lithospheric dripping — the detachment of dense lower crust into the mantle — temporarily pulled the mountains downward and allowed the river to continue flowing downhill along its current path. Key findings: - Seismic imaging reveals an anomaly interpreted as a detached lithospheric drip about 31–62 miles (50–100 km) wide at roughly 124 miles (200 km) depth. - Model timing and computed dripping speed place the separation at about two to five million years ago, consistent with estimates for when the Green River carved its canyon. - The river's canyon reaches about 2,297 feet (700 meters) deep, and the Green River later joined the Colorado River system. - The surrounding topography shows a bullseye pattern and the crust beneath the Uinta Mountains is significantly narrower than expected for their elevation, which the authors interpret as evidence of material having dripped away. - The authors state the river did not actually flow uphill; instead the land was lowered while the river continued to flow downhill and the mountains later rebounded around the established canyon. Summary: The study offers a cohesive explanation for a longstanding geological puzzle and links lithospheric dripping to changes in regional drainage and topography. Undetermined at this time.