While a potential environmental catastrophe, the lake’s dewatering presents numerous research opportunities for University of Utah geoscientists, including several who are looking to characterize the extent, characteristics, chemistry and flow of a mysterious, mostly freshwater aquifer under the playa.
In a pair of studies coming out this year, a team led by geophysicist Mike Thorne deployed electrical resistivity tomography, or ERT, lines in 30 locations around the lake’s southern and eastern margins to build 2D cross-sectional images of the subsurface.
Patchwork beneath the surface
The researchers’ discoveries, including a hidden mirabilite layer near the historic Saltair, are adding to a growing inventory of new clues U scientists are generating into the previously unknown natural processes at play under and in the lake.
“If you go along the southern shore of the Great Salt Lake, it’s much more complex than what you would ever think,” said Thorne, an associate professor in the Department of Geology & Geophysics. “You just walk out across this flat playa, everything looks the same. But underneath it, there’s a lot of lateral heterogeneity, there’s a lot of variability.”
In some places, the groundwater is salty at depth, yet freshwater is observed not far below the surface at most other locations. The findings are reported this week in the journal Geosciences, with graduate student Mason Jacketta as the lead author.
The study is part of a larger hydrology research project, involving several U geology faculty and funded by the Utah Department of Natural Resources.
“In the end, we want to know how much freshwater there is. We can see it’s a large volume,” said Bill Johnson, another U geology professor and co-author on Thorne’s paper. “What we don’t know is the flux. What can we pull out of it without harming other beneficial impacts of that groundwater?”
Much to learn about what’s below terminal lakes
The goal of Thorne and Johnson’s research is to understand the groundwater under the playa, but it’s also exploring new scientific terrain in the process and could advance our general understanding of terminal lakes, which are among the world’s most imperiled landscapes.
“This is the foundational study for doing this kind of geophysical research on terminal lakes. To my knowledge, nobody’s done this,” Thorne said. Such lakes form in basins with no outlet, so they become saline over time through evaporation that concentrates the dissolved salts. Terminal lakes are common in the Great Basin and provide important habitat for migratory birds. Around the world, these lakes are in serious peril thanks to water diversions that have dried them out, leaving behind environmental disaster zones that unleash wind-borne dust pollution.
Despite the ecological importance of terminal lakes, not much has been done to study the groundwater hidden under them until recent years, when Utah geoscientists turned their eye on the receding Great Salt Lake and the endless expanses of playa surrounding what’s left of the storied lake.
In the past few years, dozens of mounds have curiously appeared on the dry lakebed along the east shore, essentially small islands choked with phragmites. These round spots occur at places where artesian groundwater is forced to the surface under pressure through holes in the briny lens immediately below the playa, according to ongoing research led by Johnson.
The mysterious mounds prompted scientific enquiries, including Thorne’s ERT research, which began along the causeway connecting Antelope Island and Davis County mainland in 2023.