Great Salt Lake Resists Freezing

The Great (Review) Salt Lake, a vast and ancient body of water in Utah, holds a fascinating secret within its depths: a remarkable resistance to freezing. This characteristic stems directly from its unique geological past and present. As a remnant of the prehistoric freshwater Lake Bonneville, the Great Salt Lake is an endorheic basin, meaning it has no outlet to the ocean. Consequently, as rivers continually feed dissolved salts into the lake, water exits only through evaporation, leaving behind an ever-increasing concentration of minerals. Its salinity can fluctuate dramatically, ranging from approximately 5% to 29%, which is several times saltier than the average ocean.

This extraordinary salt content profoundly alters the lake's physical properties, most notably its freezing point. Unlike pure water, which solidifies at 32 degrees Fahrenheit (0 degrees Celsius), the dissolved salt ions disrupt the orderly arrangement of water molecules needed to form ice crystals. This scientific principle, known as freezing point depression, means that the lake's water must reach significantly colder temperatures before it can freeze. In its open waters, the Great Salt Lake's freezing point can drop to around 22 degrees Fahrenheit (-5.5 degrees Celsius), with even lower thresholds in its highly saline northern arm, which can reach up to 28% salinity.

While the Great Salt Lake almost never completely freezes over, thin ice can occasionally form, particularly in areas where freshwater inputs dilute the salinity or during prolonged periods of extreme cold. It is not uncommon for less dense freshwater from tributary rivers to freeze on the surface, creating floating ice sheets. However, the majority of the lake remains liquid, playing a vital role in local meteorology by contributing to "lake-effect" snow in the nearby mountains. This unfrozen expanse also sustains a unique ecosystem of brine shrimp and brine flies, which form the base of a food web supporting millions of migratory birds.