SALT LAKE CITY — At a moment when Utah’s water future looks bleaker than it has in decades, scientists at the University of Utah have uncovered something unexpected beneath the cracked, dusty bed of the Great Salt Lake: a potentially vast reservoir of freshwater, sitting just below the surface and stretching miles underground.
The discovery, published in February in the Nature-affiliated journal Scientific Reports, comes as the state grapples with its worst winter on record. Snowpack statewide peaked three weeks ahead of schedule at record-low levels, and experts have already warned that the dry, warm conditions could trigger an earlier and more intense wildfire season. For a region that depends on mountain snowmelt to replenish its lakes and reservoirs, the timing of the finding could not be more striking.
Unexpected Finding
While the lake’s surface is hypersaline, among the saltiest water bodies in the Western Hemisphere, a thin brine layer averaging only about 10 to 15 meters deep is apparently all that separates that surface from a much larger body of freshwater below. Beneath that thin salty lid, researchers found freshwater-saturated sediments extending to depths of 3 to 4 kilometers, roughly 10,000 to 13,000 feet.
Some of that water may be ancient.
About 15,000 years ago, freshwater Lake Bonneville covered the entire region. As the climate shifted and the lake shrank and salinized into what is now the Great Salt Lake, freshwater became trapped beneath the lakebed. Researchers believe that ancient reservoir, fed over millennia by groundwater flowing westward from the Wasatch Mountains, may still be largely intact underground.
The U research team used a helicopter-borne electromagnetic survey system developed by a Canadian firm to essentially X-ray the geology beneath Farmington Bay and Antelope Island off the lake’s southeastern shore. Flying 248 line kilometers in a single day last February, the crew collected data that allowed scientists to map the boundary between salty and fresh water underground. Crucially, the geophysical findings were independently confirmed by direct measurements of water chemistry from cores drilled at the site, work published in a companion paper in the Journal of Hydrology this spring.
“The unexpected part of this wasn’t the salt lens that we see near the surface across the playa,” said Bill Johnson, a U geology and geophysics professor and co-author on both papers. “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.”…