A potentially huge underground reservoir of freshwater beneath the Great Salt Lake is coming into sharper focus with a new study that used airborne electromagnetic (AEM) surveys to X-ray geologic structures under Farmington Bay and Antelope Island off the lake’s southeastern shore.
An analysis of this data by University of Utah geophysicists shows that freshwater saturates the sediments beneath the lake’s hypersaline surface to depths of 3 to 4 kilometers, or about 10,000 to 13,000 feet. The helicopter-borne geophysical survey was conducted last year after U scientists documented freshwater welling up under pressure at several spots on the lake’s exposed playa in Farmington Bay, manifesting as strange phragmites-choked mounds.
The study demonstrated for the first time the ability of AEM methods to detect freshwater underneath thethin layer of conductive salt water at the surface of the Great Salt Lake, according to lead author Michael Zhdanov. His team also characterized the spatial extent of the freshwater reservoir beneath Farmington Bay and studied the potential depth of freshwater-saturated sediments by delineating the basement structure.
“We were able to answer the question of how deep this potential reservoir is, and what its spatial extent is beneath the eastern lake margin. If you know how deep, you know how wide, you know the porous space, you can calculate the potential freshwater volume,” said Zhdanov, a distinguished professor of geology & geophysics and director of the Consortium for Electromagnetic Modeling and Inversion, or CEMI.
A larger state-funded research effort focused on a newly discovered aquifer
The results appear in the Nature-affiliated journal Scientific Reports. This study is part of a larger research project led by the U’s Department of Geology & Geophysics and funded by the Utah Department of Natural Resources to understand the groundwater beneath Great Salt Lake, the largest terminal lake in the Western Hemisphere.
Overseen by some of the department’s most senior faculty and their graduate students, this effort has already resulted in two other important papers, with more to follow.
The evidence produced in this new study suggests that freshwater is entering the subsurface toward the lake’s interior, not its periphery as would be expected, according to hydrologist Bill Johnson, a co-author on all the Great Salt Lake groundwater papers.
“The unexpected part of this wasn’t the salt lens that we see near the surface across the playa. It’s that the freshwater underneath it extends so far in towards the interior of the lake and possibly under the entire lake. We don’t know,” Johnson said on a recent appearance on KPCW’s Cool Science Radio show. “What we would normally expect as hydrologists is that the brine would occupy the entire volume underneath that lake. It’s denser than the freshwater. You’d expect the freshwater from the mountains to come in somewhere at the periphery. But we find it’s coming in towards the interior. And there’s what appears to be a deep volume of this freshwater coming in underneath that saline lens.