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Environment

Wild About Utah: Mirabilite Mounds At The Great Salt Lake

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Mary Heers
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Back in October 2019, the ranger at the Great Salt Lake State Park began to notice a white mound forming on the sand flats behind the visitor center. The white mounds turned out to be hydrated sodium sulfate, known as mirabilite, which was being carried to the surface by the upwelling of a fresh water spring. 

Since the 1940's geologists have known that in this area, 30 inches below the surface, there was a three to six-foot thick shelf of mirabilite. They knew about the freshwater springs. What was new was cold air. Since this stretch of sand was no longer underwater, the mirabilite carried to the surface now stayed there as crystals, piling up on each other, puddling and spreading out. One mound rose to a height of three feet.

 

When the mounds started to form again this winter, I jumped at the chance to to go and take a look. I must admit at first I was a little underwhelmed at the size, perhaps because the Kennecott Smelter Stack nearby dominates the view, rising to 1,215 feet, roughly the same height as the Empire State Building. But the park ranger got my attention when she told us that mirabilite mounds have only been seen in four places in the world—the Canadian Arctic, Antarctica, Central Spain, and Utah. Just seeing them turns out to be a rare winter treat.When the air warms to 50 degrees, the mirabilite will crumble into a fine white powder and disappear. 

 

My mind flashed back to a trip I'd made to the other end of the lake eight years ago. I'd just graduated from the docent training class at the Utah Museum of Fine Art, and a friend and I wanted to celebrate by having high tea at the center of the Spiral Jetty, a 1,500 foot, long, 15 mile wide coil of black basalt rock—a stunning example of land art jutting out from the northern shore. We'd been warned that it might be underwater, but when we arrived we were delighted to find we could easily walk to the very center of the spiral as the lake water gently lapped at the edges of our shoes. We clinked our tea cups, and toasted the greatness of the lake.

 

Suddenly I wanted to see the jetty again, so I hopped in my car and drove to the remote site. I saw the Spiral Jetty was now high and dry. Drifting sand had already started to bury parts of it. The water's edge was now over 300 yards away. I thought about the millions of migratory birds that would be arriving in the spring to rest and feast on the tiny treasures of the lake, the brine shrimp. I hoped the smaller lake would still be enough for all of them.

 

The recent words of the director of Friends of the Great Salt Lake, Lynn de Freitas, rang in my head: "The Great Salt Lake is a gift that keeps on giving. Just add water."