Scientists discover potentially huge freshwater reservoir hidden beneath the Great Salt Lake

Scientists have discovered a freshwater reservoir beneath the surface of Utah’s Great Salt Lake, and a new study shows it may extend throughout the lake and beyond.

This reservoir extends up to 2.5 miles (4 km) deep beneath certain spots on the eastern edge of the lake, where in recent years strange reed-covered mounds have grown out of the dry surface. If future studies confirm that the reservoir is as large as preliminary results suggest, the fresh water could help remediate areas where the lake bed has cracked and produced toxic dust, the researchers said.

“When we first realized we had discovered this, we were very excited,” study lead author Michael Zhdanov, director of the Electromagnetic Modeling and Inversion Consortium and distinguished professor of geology and geophysics at the University of Utah, told Live Science. “I think that’s very important.”

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Researchers have long suspected that a freshwater source lies beneath the appearance of mysterious mounds of reeds or phragmites in the dry southeastern corner of the Great Salt Lake. Phragmites require an abundance of fresh water to grow, and the researchers believe that groundwater must be rising beneath Farmington Bay’s dry lake bed.

Zhdanov said samples taken from the mound showed the presence of fresh water. “So the question was, where is this water coming from? And the hypothesis was that it was probably groundwater coming from the surrounding mountains,” he says.

To understand the plumbing beneath the mound, Zhdanov and his colleagues conducted an airborne electromagnetic survey over a 10-square-mile (25-square-kilometer) portion of the Great Salt Lake. With the help of Expert Geophysics, the researchers flew a helicopter carrying a suspended circular device that sent electromagnetic pulses downward in a long line over the lake. A ball suspended in the center of the device intercepted these signals as they bounced back, producing data that software could decipher and map the freshwater sediments beneath the lake.

The Great Salt Lake is a large saltwater lake with a surface area of ​​approximately 1,700 square miles (4,400 square kilometers). Salt water is highly conductive, so scientists weren’t sure if the electromagnetic pulse would penetrate the lake and the sediments beneath it to provide a clear image. “This was just an experimental project to see if we really get this result,” Zhdanov said.

However, when the map returned, it showed a subsurface layer of freshwater throughout the study area. Zhdanov said the sediments beneath the Great Salt Lake are saturated with fresh water, which likely dripped from the surrounding mountains as snowmelt and accumulated over thousands, if not millions, of years.

“The results were amazing,” he said. “Of course, that was a small portion of the total area of ​​the Great Salt Lake. We need to expand the study to make a final conclusion that this reservoir is under the entire area.”

The results, published February 27 in the journal Scientific Reports, showed a layer of freshwater in the sediments beneath the lake, which ranges from 330 feet (100 meters) to 2.5 miles deep. Zhdanov said some kind of “cap” rock likely prevents the fresh water from mixing with the lake’s salt water, but more research is needed to figure this out, as fresh water could rise beneath the reed-covered hills.

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In addition to collecting electromagnetic data, the aerial survey also collected magnetic data, which scientists used to map the lake’s deep geology. They found that water-tight “underground” rocks form the lower limit of the freshwater reservoir, and faults in these rocks could explain sudden changes in the reservoir’s depth, Zhdanov said.

If the reservoir were spread across the Great Salt Lake, it could provide a solution to the toxic dust clouds emitted by expanses of exposed lake bed. Since 1986, human water consumption, drought, and high evaporation rates due to climate change have lowered the lake by approximately 22 feet (6.7 m).

Exposed areas of the lake bed dry out and erode, creating dangerous dust pollution in nearby populated areas. For example, a 2023 study found that Salt Lake City lies directly downwind of the lake and could see a significant increase in toxic air pollution in the coming years.

Zhdanov said fresh water from the reservoir could be used to moisten the lake bed and reduce pollution. Farmers in the area may also collect water for irrigation, he added, but more research is needed.

The results suggest freshwater reserves may be hidden within Utah or elsewhere, Zhdanov said. “The bottom line is that this project demonstrated that aerial geophysical research can be used to identify groundwater reserves in deserts like Utah,” he said.