Great Salt Lake’s Mirabilite Mounds
March 23, 2022
Photographer: Ray Boren
Summary Author: Ray Boren
Due to long-term drought, exposed shorelines of the Great Salt Lake are in places speckled with crystalline hummocks that resemble the larger terraced springs of Yellowstone National Park. Unlike the national park’s travertine-lined hot springs, however, the Utah phenomena are mirabilite mounds. These unique landforms take shape over the cold winter months and when shoreline water has withdrawn enough to reveal usually submerged springs.
This process has been the case for the past few years, notably on the south shore beach at Great Salt Lake State Park and Marina, as illustrated in the above photographs taken on February 1, 2022. The first photo shows several mounds, with the lake’s edge and Stansbury Island in the distance, while the second picture is a closeup of one of the formations.
A layer of sodium sulfate underlies the lakebed surface, so when spring water rises in the winter cold, mirabilite crystals effloresce upon exposure. This crystallization process creates the mounds and their sequences of small terraces. The mineral mirabilite — from the Latin “sal mirabilis” for “wonderful salt” — is found in saline lakes and on playas around the world. The rare mounds around Great Salt Lake are not composed of sodium chloride, also known as common table salt (NaCl), but instead of hydrated sodium sulphate (Na2SO4•10H2O). This compound is also called Glauber’s salt and has various medical applications.