Falling water levels at Utah’s Great Salt Lake exposed mysterious circular mounds; freshwater springs beneath them may supply up to 12% of the lake’s water budget |
Satellite images from 2025 show dozens of circular mounds exposed by falling water levels. Satellite images revealed these features across Farmington Bay, Ogden Bay and Bear River Bay. The mounds stood out from the surrounding dry lakebed, with dense reeds growing at their centres. Researchers traced this unusual vegetation to freshwater springs flowing directly into the lake basin.The discovery points to an extensive underground freshwater reservoir that scientists had not previously recognised. According to Nasa Earth Observatory, the springs may account for as much as 12% of the lake’s total water budget, far above the roughly 3% previously assumed by hydrologists.
Satellite images uncover strange circular mounds at Great Salt Lake
As Great Salt Lake’s water levels fell, dozens of unusual circular features emerged along the eastern edge of its drying lakebed. They appeared in parts of Farmington Bay, Ogden Bay and Bear River Bay, where satellite images captured areas that had previously been underwater.University of Utah researchers had encountered possible signs of these features years earlier while travelling by airboat through the lake’s shallow bays. They noticed circular patterns disturbing the water’s surface but could not explain their cause. As more of the lakebed became exposed, similar shapes appeared in images captured by Landsat and other satellites.A Landsat 9 image taken on September 13, 2025, showed at least seven features clustered in Ogden Bay. An image of the same area from September 15, 2011, showed how higher water levels had concealed them.
PC: Nasa Earth Observatory
How did researchers investigate the mysterious mounds at Great Salt Lake
The unusual satellite images prompted researchers to organise field expeditions to investigate several features. They travelled across thick patches of reeds to reach the centres of the vegetation-covered mounds, using snow bikes and garden tools to avoid damaging the exposed lakebed.William Johnson, a geologist at the University of Utah, said, “It took some work to reach certain sites since we wanted to avoid using vehicles or other modern equipment that might damage the playa”.Once at the sites, researchers installed piezometers and other monitoring equipment at different depths and distances from the centres of the features. These instruments helped them measure the pressure and salinity of the underlying water. The measurements revealed a clear pattern. Groundwater was salty towards the edges of the mounds but fresher near their centres, where phragmites reeds grew in circular formations.
What could hidden freshwater springs reveal about Great Salt Lake
The reeds help distinguish the mounds from the surrounding bright playa in satellite images. Researchers identified dozens of these features, while higher-resolution satellite sensors revealed dozens of smaller examples to the southwest and south of the main cluster.After conducting aerial electromagnetic surveys, the team estimated that probably hundreds of groundwater-fed oases could be spread across newly exposed sections of Great Salt Lake’s playa.Johnson described the features as ‘windows’ into an extensive underground freshwater reservoir that scientists had not previously realised existed. The discovery also changed estimates of how much groundwater enters the lake.Researchers estimate that freshwater discharge from these springs may account for as much as 12% of Great Salt Lake’s total water budget. This is considerably higher than the roughly 3% that hydrologists had previously assumed these springs contributed, highlighting the significance of the newly identified freshwater inflow.
Freshwater springs may help reduce dust from the drying lakebed
Johnson said the newly identified freshwater inflow could have practical benefits, particularly in limiting dust generated by exposed sections of the lakebed. He cautioned that the discovery did not represent a vast new freshwater resource suitable for large-scale extraction.Dried lakebeds can produce substantial amounts of dust because they contain fine-grained sediments and have little vegetation to hold the material in place. Surface water makes it harder for winds to lift dust and fuel dust storms.
