Great Salt Lake is a shallow, closed-basin lake in northern Utah. Its surface area and concentration of dissolved solids vary in response to both annual and long-term climatic changes. The lake gains water mainly as streamflow from mountains to the east and loses water through evaporation. In 1965, at a lake-surface altitude of 4,194 feet, the surface area was about 1,000 square miles, and the maximum measured depth was 27 feet.
Studies to define the variations in chemical and physical characteristics of the brine began in 1963, and detailed sampling of the lake at 29 sites was made in October 1965 and May 1966. Data resulting from concurrent sampling of the 29 sites indicated that four types of brine coexist in the lake.
The concentration of dissolved solids in the Great Salt Lake brine has always varied from place to place and with depth. Inflow, evaporation, currents, wind, and density differences resulted in brine stratification in the deep parts and brine concentration in the shallow, isolated parts of the lake.
Completion of a railroad causeway by the Southern Pacific Co. in 1957 divided the lake into two parts and altered the movement of brine. The northwestern part of the lake was essentially cut off from direct fresh-water inflow by the causeway, and as a result it was saturated and well mixed from 1963 to 1966. During the main evaporation season (June-October), a layer of salt crust was precipitated on the lakebed north of the causeway. Near Rozel Point the salt crust contained 99.6 percent sodium chloride.
The southern two-thirds of the lake receives over 90 percent of the surface inflow and since 1957 has rarely reached saturation. The southern part of the lake is not well mixed, and three types of brine have been identified by their location, concentrations of specific ions, and concentrations of dissolved solids. These brines are located (1) in a zone from the surface to a depth of 16 feet, (2) in a zone below 16 feet south of the causeway, and (3) in the zone below 16 feet in the south end of the lake.
The shallow zone of brine in the southern part of the lake varies in concentration of dissolved solids from season to season because of the interplay between inflow and evaporation. Brine in this zone is usually the most dilute of any brine in the lake.
The two deep brines in the southern part of the lake contain almost the same concentration of dissolved solids, which is greater than that of brine in the shallow zone but not quite as great as that of brine north of the causeway. The concentrations of dissolved solids of the deep brines also vary seasonally.
Brine in the deep zone near the south side of the causeway is maintained by a density current that flows at depth from the northern part of the lake through the causeway.
Brine in the deep zone at the south end of the lake is distinguished from the three other brines in the lake by its high concentration of sodium ion and its low concentration of sulfate ion. This brine might result from the inflow of ground water through the zone of sulfate reduction at the lakebed.
Brine north of the causeway is reddish-brown and visibility of an object placed in it is limited to about 2 feet, whereas brine south of the causeway is green and bottom features 15 feet below the surface can often be clearly seen.
Studies describing the relations among the interchange of brine through the causeway, the thickness of the salt crust, the concentrations of dissolved solids in the brine, and identifying the source of deep brine at the south end would provide information needed for future lake management.