Thursday, December 17, 2020

The Crazy Colorado River

Recent geological research indicates that the Colorado river's route from the Colorado Plateau was influenced by tectonic deformation and vaciliating sea levels that caused a series of stops and starts between 6.3 and 4.8 million years ago. A team led by geologist Rebecca Dorsey of the University of Oregon has made a case for a complex history of the river, showing that, contrary to conventional thinking, a river's connection to the ocean is not a once-and-done deal.

"The birth of the Colorado River was more punctuated and filled with more uneven behavior than we expected," Dorsey said. "We've been trying to figure this out for years. This study is a major synthesis of regional stratigraphy, sedimentology and micropaleontology. By integrating these different datasets we are able to identify the different processes that controlled the birth and early evolution of this iconic river system."

Dorsey said that no single process controlled the Colorado River's initial route to the sea. "Different processes interacted in a surprisingly complicated sequence of events that led to the final integration of that river out to the ocean," she said.

The region covered in the research stretches from the southern Bouse Formation, near present-day Blythe, California, to the western Salton Trough north of where the river now trickles into the Gulf of California. The Bouse Formation and deposits in the Salton Trough have similar ages and span both sides of the San Andreas Fault, providing important clues to the river's origins.

The Colorado River starts in the peaks of the Rocky Mountain in the United States and flows into Mexico, where it empties into the Upper Sea of Cortez. Its natural course has varied over thousands of years, and the demand for water to serve an estimated 40 million people now exceeds the river’s supply, resulting in the desiccation of the Colorado’s last hundred miles.

The Colorado River's seven basin states are managing water under the Drought Contingency Plan, an agreement to safeguard water levels at the river's two main reservoirs, Lake Mead and Lake Powell. The two lakes are critical to providing water in times of drought. The Colorado River Basin states are Arizona, California, Colorado, Nevada, New Mexico, Utah, and Wyoming.

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