Evaporite can also cause uplift | PostIndependent.com

Evaporite can also cause uplift

Dennis Webb
GSPI News Editor

The same underlying factors causing regional collapse are also resulting in localized cases of uplifting.

That’s because evaporites don’t only dissolve. They also flow, “kind of like putty underground,” said geologist Bob Kirkham.

As rivers cut into the earth, they remove rock. Evaporite under pressure from overlying rock tends to flow toward valleys, where pressures are less. There, it oozes up to the earth’s surface.

This oddity is illustrated by some Roaring Fork Valley river terraces, which lean away from the river.

Kirkham said a good example is what geologists call the Bershenyi terrace – home to the Bershenyi ranch and the proposed Red Feather Ridge subdivision – which is more than 100 feet higher on its northern, downstream end than its upstream end.

A good vantage point to see it is from the first switchback up Red Canyon Road, south of Glenwood Springs.

But this uplifting isn’t keeping up with the larger regional collapse. Vince Matthews, senior science advisor of the Colorado Geological Survey, said elevation drops correspond closely to the amount of evaporite dissolution that is occurring.

Geologists can estimate the average amount of evaporites being carried downstream by area rivers. If they assume that rate of dissolution over 3 million years, they can determine the volume of evaporite removed over time, and how much collapse should have occurred.

“The amount of (actual) collapse correlates quite closely to the amount of dissolution of evaporite,” Matthews said.


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