Mirabilite Mounds and The Great Salt Lake

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 3 – 6 foot thick shelf of mirabilite. They knew about the fresh water springs What was new was cold air. Since this stretch of sand was no longer underwater, the mirabilite carried to the surface stayed there as crystals, piling up on each other, puddling and spreading out. One mound rose to the height of 3 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 entire 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 ten 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 foot 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 of 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 a 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.”

This is Mary Heers and I’m Wild About Utah.

Credits:
Photos: Courtesy & Copyright Mary Heers, Photographer
Featured Audio: Courtesy and Copyright Kevin Colver https://wildstore.wildsanctuary.com/collections/special-collections/kevin-colver
Text & Voice: Mary Heers, Generous Contributor, Utah Public Radio
Additional Reading: Lyle Bingham, Webmaster Bridgerland Audubon Society

Additional Reading

Mirabilite Spring Mounds Near Great Salt Lake Marina, Utah Geological Survey (UGS), Utah Department of Natural Resources, https://geology.utah.gov/popular/general-geology/great-salt-lake/mirabilite-spring-mounds/

Mirabilite, Mindat.org, Hudson Institute of Mineralogy, https://www.mindat.org/min-2725.html

Tabin, Sara, Rare salt formations return to Great Salt Lake’s shores; take a tour while they last, The Salt Lake Tribune, Jan. 13, 2021, https://www.sltrib.com/news/2021/01/14/rare-salt-formations/

USGS 412613112400801 The Great Salt Lake at Spiral Jetty, Site Map for the Nation, U.S. Geological Survey(USGS), U.S. Department of the Interior, https://waterdata.usgs.gov/nwis/nwismap/?site_no=412613112400801&agency_cd=USGS

Case, William, GEOSIGHTS: PINK WATER, WHITE SALT CRYSTALS, BLACK BOULDERS, AND THE RETURN OF SPIRAL JETTY!, Survey Notes, v. 35 no. 1, Utah Geological Survey (UGS), Utah Department of Natural Resources, January 2003, https://geology.utah.gov/map-pub/survey-notes/geosights/spiral-jetty/

Board & Staff, Friends of the Great Salt Lake, https://www.fogsl.org/about/board-staff

Salt Lake Brine Shrimp, https://saltlakebrineshrimp.com/harvest/