Angelic Anderson crouched down and ran her fingertips across a large white mound that rose several inches from the surface of the bone-dry lakebed. As a park ranger at the Great Salt Lake State Park in northern Utah, she’s accustomed to seeing the massive lake’s waterline recede, especially during dry months when there’s little to no rainfall. However, over the course of the last few winters, she and other rangers have noticed something strange happening along the lake’s normally pancake-flat southern shoreline, with large white lesions cropping up in areas that are normally just sand.
“We were very concerned,” Anderson told me this spring. “One of our rangers contacted the Utah Geological Survey looking for answers.”
Geologists from the UGS reviewed photos and took samples of the chalky white heaps and concluded they’re piles of salt known as mirabilite mounds, or Glauber’s salt. These rare geological formations occur when underground water reacts with minerals and burbles to the surface, intermingling with the cold, winter air to form white crystals. Normally this portion of the lake would be covered in water and wouldn’t be susceptible to this phenomenon, however, for the last several winters, the fragile mounds have become a common occurrence on the sandy lakeshore.
“In 2019, the first year we spotted them, there were about four formations,” Anderson said. “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 10.67 m long.”
According to the UGS, one possible reason why more are developing is because, as the mounds grow, “they eventually seal off their spring water source, causing the groundwater to find a new pathway to the surface,” causing new growths to develop.
In the three years since, lake levels have dropped significantly, hitting record lows, which offers the perfect conditions for the mounds to form. According to the U.S. Geological Survey (USGS), in July 2021, average daily water levels dropped an inch, the largest known dip since 1963 and the highest change since the organisation began recording levels back in 1847. On July 3, 2022, USGS reported that the lake had hit its lowest level ever on record. Even without these scientific measures, it’s obvious that lake levels are severely low. At the Great Salt Lake Marina, about a five-minute walk to where the mirabilite mounds have been forming, the slips where sailboats normally bob up and down in the water are dry, and people have transported their boats to dry docks overlooking the marina. Research shows that the mounds begin to form when the water’s elevation falls below 1,278.33 m.
“When lake levels are higher, the underground springs are normally covered in salt water,” says Elliot Jagniecki, a senior geologist with the Utah Geological Survey. “So, they’re usually not visible, but with the lower water levels, now we can see them form.”
The Great Salt Lake is no stranger to geological shifts, especially as droughts have become more rampant throughout Utah and the rest of the U.S. West. It’s the largest saltwater lake in the Western Hemisphere, stretching approximately 121 km in length and 56 km in width and covering 4,400 , reaching depths of 10.06 m. Today’s lake is defined as a terminal lake, meaning it doesn’t have any natural outlets like rivers flowing from it and loses water mainly through evaporation.
The lake’s entire surface area has shrunk by more than 40% since 1875, when federal monitoring began, according to Audubon, due to things like evaporation and agricultural practices. This shrinkage can be confirmed by satellite images that show the recession. Things have gotten so desperate that local lawmakers have discussed the outlandish idea of piping in seawater from the Pacific Ocean to fill the lake.
The lake we see today is actually what remains of an even larger body of water known as Lake Bonneville that existed during the most recent ice age. Lake Bonneville was massive, with an area of 51,282 , or roughly 10 times that of the Great Salt Lake. Much of the salt and minerals found in today’s lake are remnants from Lake Bonneville, resulting in the sodium-sulfate-rich spring water that runs beneath the lakebed. This could help explain why the mounds are forming in the first place.
Another variable to their formation is that outside temperatures need to be sub-freezing, which explains why mirabilite mounds are only spotted on the shore during the winter. In order for the mirabilites to form, conditions must be a perfect mix of sub-freezing temps and dry. This is also why similar formations have been spotted in polar regions, including Antarctica.
“We’re thinking the mounds are a response to a few things,” Jagniecki says, “including low lake levels, the arid climate, and low water input.”
In nearby Salt Lake City, several local media outlets have reported on the mysterious mounds, drumming up interest, which led to the state park offering ranger-led tours to the public, with slots filling up quickly. A local university has also started collecting samples to study the biological makeup of the formations. And a post on the Utah State Parks Blog even pointed out a possible Mars connection that could potentially serve as an analogue for researchers, since the Red Planet shares similar attributes to the lakeshore, including being an arid environment.
“[The Mars connection] is more of a hypothesis and is based on satellite imagery,” Jagniecki says. “Images show that Mars does have topographic mounds that some researchers think could be similar in composition, but it’s still an unknown.”
The mounds disappear with the arrival of summer, leaving behind little more than a thin layer of white powder called thenardite. However, if the past few years are any indication, it’s likely that these ghost-like formations will sprout up again soon.
Jennifer Nalewicki is a Salt Lake City-based journalist. Her work has been featured in Smithsonian Magazine, Scientific American, Live Science, and more.
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