The largest salt lake in the Western Hemisphere contains so many dissolved minerals that bathers find it difficult to sink—or even swim. You can no more sink [in Great Salt Lake] than in a claybank,” Horace Greeley observed. He exaggerated little: the lake’s briny water, in some places nearly eight times saltier than seawater, buoys up bathers so that their heads and shoulders remain above water. Even swimming in it is difficult.
As impressive as it is today, how-eve Great Salt Lake is but a remnant of an ancient lake that once extended from Utah into Nevada and Idaho. This ancestral lake, which geologists call Lake Bonneville, occupied some 20,000 square miles (52,000 square kilometers) and was about 20 times the size of the present lake. Former shorelines can still be detected as step like terraces on surrounding mountainsides. The highest of these old shores is about 1,000 feet (300 meters) above the lake’s present level.
Lake Bonneville was a product of the immense glaciers that covered much of North America during the Ice Age. As the climate slowly warmed, meltwater from the glaciers filled the natural depression until, in time, Lake Bonneville overflowed into the Pacific by way of the present-day Snake and Columbia river valleys.
With the final retreat of the glaciers, the climate became still warmer—and drier. Evaporation from the ancestral lake eventually exceeded the flow of water coming in, and the lake shrank. (Depending on climatic changes, the lake continues to vary dramatically in size and depth from year to year.) Besides shrinking the size of the lake, the evaporation also concentrated the salts and other minerals that were dissolved in its waters.
Today three major rivers flow into the lake, but none flows out: water leaves only by evaporation. Scientists estimate that more than 3 million tons (2.7 million metric tons) of salts are added to the lake each year. And it is these dissolved salts that make the lake’s waters much heavier than seawater—and swimmers so much more buoyant. Despite the high concentration of salts, a surprising variety of life thrives in the lake, from bacteria and brine shrimp to large waterfowl.
Every year thousands of tons of table salt, potassium sulfate, and other valuable minerals are harvested from the lake. In a complex process that involves pumping the water through a series of shallow ponds, the brine is left to evaporate under the burning desert sun. When the water is gone, the various minerals are scooped up and processed.
Similar solar drying forms the vast Bonneville Salt Flats to the west of the lake. Although wet for much of the year, this remnant of the ancestral lake dries out during the hot summer months and forms a surface so hard that it is used as an automobile race course. Thus land speed records have been made—and broken—on what was once the bottom of a lake. Anna live in Prague and writes for various travel guides.