New geophysical surveys by U geoscientists reveal a hidden, dynamic aquifer system under the lake's exposed playa
Press release from Brian Maffly, University of Utah Science Communication Manager
As drought and upstream diversions have shrunk Utah’s Great Salt Lake by roughly 70% since 1989, more than 800 square miles of lakebed have been exposed. While the lake’s retreat poses serious environmental risks, it is also opening unprecedented scientific opportunities.
Researchers at the University of Utah are taking advantage of this rare moment to peer beneath the playa and map a mysterious aquifer system hidden below the lake’s southern and eastern shores. Using advanced geophysical tools, the team has discovered a surprisingly complex underground landscape—one that includes shallow freshwater pockets, thick layers of brine and even unusual mineral formations.
In a new study published in Geosciences, geophysicist Mike Thorne and his colleagues report results from electrical resistivity tomography (ERT) surveys conducted at 16 locations. The method works by placing electrodes in the ground, sending electrical current through the subsurface and measuring resistivity. Because salty water conducts electricity more easily than fresh water, resistivity values enable scientists to estimate groundwater salinity.
Key Takeaways:
- Groundwater beneath Great Salt Lake’s playa on the south shore is highly variable, ranging from shallow freshwater to thick brine layers just meters apart.
- Researchers mapped a buried mirabilite layer near Saltair, which traps brine and contributes to seasonal evaporite mound formation.
- Freshwater is abundant beneath parts of the eastern shore, particularly Farmington Bay, raising questions about volume, recharge and sustainability.
- Scientists may have identified a rare saltwater “fingering” process, observed only once before in nature.
A Patchwork Beneath the Surface
The team focused on three south shore areas.
At Burmester and Saltair, they found thick layers of highly saline groundwater just a few meters below the surface. Near Saltair, the brine is capped by a hard mineral layer of mirabilite—also known as Glauber’s salt. Cracks in this mineral crust allow brine to rise during colder months, forming small evaporite mounds on the playa.
Farther east near Lee’s Creek, however, the picture changes. There, researchers detected freshwater as shallow as three meters below ground. This freshwater likely comes from mountain recharge from the Wasatch Range or may even be a remnant of ancient Lake Bonneville, which filled the basin until about 14,000 years ago.
Freshwater Under Farmington Bay
In a forthcoming study targeting Farmington Bay on the lake’s eastern shore, Thorne’s team will report even more surprising results. In that area—adjacent to the Wasatch Mountains—groundwater below about four meters is almost entirely fresh.
According to co-author Bill Johnson, understanding this freshwater resource is a central goal of the broader research effort, funded by the Utah Department of Natural Resources.
“In the end, we want to know how much is there,” Johnson said. “We can see it’s a large volume. What we don’t know is the flux—what can we pull out of it without harming other beneficial impacts of that groundwater?”
Thorne’s preliminary results also suggest a rare physical process occurring beneath Farmington Bay. In certain locations, dense saltwater appears to sink downward into underlying freshwater in finger-like patterns—a phenomenon known as convective instability. If confirmed, it would be only the second documented natural example of this process worldwide.
