Massive, Strange White Structures Appear on Utah's Great Salt Lake

The mysterious, huge white mounds that have begun to appear on the Great Salt Lake in Utah, which are getting larger and more frequent, have now been explained.

The Utah Geological Survey (UGS) investigated the mysterious structures and concluded that they're actually piles of salt known as mirabilite mounds. Mirabilite is also known as Glauber's salt and has the chemical formula Na2SO4•10H2O—normal table salt has the formula NaCl, for comparison.

"In 2019, the first year we spotted them, there were about four formations," Angelic Anderson, a park ranger at the Great Salt Lake State Park, told Gizmodo. "But this year, we've recorded 15, the most we've ever seen. They've also gotten bigger, with one measuring three feet in height. Last year there was also one that was 35-feet long."

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Stock image of the Great Salt Lake. Strange white mounds on the lake's shore have been found to be build-ups of mirabilite, and are getting larger with each passing year. iStock / Getty Images Plus

The Great Salt Lake, on the outskirts of Salt Lake City in Utah, is the largest saltwater lake in the Americas and eighth largest in the world.

According to the UGS, these mysterious mounds are formed as sodium sulfate (Na2SO4) rich spring water from beneath the ground hits the cold winter air, causing mirabilite crystals to form and build up into a pile.

These mounds are normally only formed in the colder months, as mirabilite is most stable and precipitates at temperatures under 32 degrees Fahrenheit, or the temperature that liquid water freezes. Normally this area of the lakebed would be submerged, so the salt would have just dissolved into the lake water. However, the Great Salt Lake has been drying up.

According to the U.S. Drought Monitor, nearly the entire circumference of the Great Salt Lake is classified as being in "Extreme Drought," with the easternmost section being under "Severe Drought." The lake's water levels have dropped continuously with each recent year, and as of September 7, was measured to be 4,189.02 feet above sea level. This is the lake's lowest water levels since records began in 1847. The previous record low was recorded in October 2021 at 4,190.2 feet above sea level.

The mounds begin to form when the water's elevation falls below 4,194 feet, according to the UGS.

"When lake levels are higher, the underground springs are normally covered in salt water," Elliot Jagniecki, a senior geologist with the UGS, told Gizmodo. "So, they're usually not visible, but with the lower water levels, now we can see them form."

The UGS hypothesizes that there are multiple mounds because as the piles grow, they eventually seal off their spring water source, causing the groundwater to force to the surface via a new path.

These mounds aren't the only strange things being seen emerging from newly dried-up lakes and rivers. A century-old steamboat wreck was uncovered this week in the Missouri River after its water levels dropped dramatically, and in Texas, the Paluxy River in Dinosaur Valley State Park was so dry that undiscovered dinosaur footprints were revealed on the riverbed.

Even some human bodies have been found in Lake Mead, which in 2022 has dropped to its lowest water level since it was constructed. Five separate sets of human remains have been discovered, one of which was found inside a barrel, and was peppered with bullet holes.