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T258 Atlas p.2 Great Salt Lake, Utah Lake level fluctuations, ancient shorelines Significance: Great Salt Lake is the largest salt water lake in the Western Hemisphere. Lake levels rose up to 2 meters (6 feet) during the early and mid 1980's, due to abnormally heavy precipitation during the spring and summer and heavy amounts of snowfall in the surrounding mountains during the winter. Expansion of lake surface because of the abnormally heavy precipitation caused erosion of the shorelines and damage to communities and properties around the lake. Lake levels now are the highest since the 1880's. Reports indicate that isolated standing water remains on the Bonneville Salt Flats to the Nevada state line. Geomorphologists will be interested in the number of outwash plains or alluvial fans generated by recent heavy precipitation and snowmelt. Shuttle photography of Great Slat Lake has been compared to Skylab photographs (1973 -74). Physical Characteristics: The Great Salt Lake is oriented northwest to southeast. The lake is approximately 130 kilometers long and 48 kilometers wide. The marked difference in water color seen between the northern and southern basins is due to a higher saline level, more biological activity and shallower lake depth in the north. As impressive as it is today, the Great Salt Lake is only a remnant of an ancient lake that extended from Utah into Nevada and Idaho about 15,000 years ago. Called Lake Bonneville, it occupied some 52,000 square kilometers (20,000 miles) and was about 20 times the size of the present lake. Former shorelines can still be detected as step-like terraces on the surrounding mountainsides. Lake Bonneville was a product of the immense glaciers that covered much of North America during the last glacial period. As the glaciers retreated and climate turned warmer and drier, evaporation exceeded the inflow of water and the lake shrank. Besides shrinking the size of the lake, the evaporation also concentrated salts and other minerals that were dissolved in its waters. Depending on climatic changes, the lake continues to vary in size and depth from year to year. Today three major rivers flow into the lake; water leaves only by evaporation. It is estimated that more than 3 million tons of salts are added to the lake each year. Every year thousands of tons of table salt and other valuable minerals are harvested from the lake. 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 not summer months and forms a surface so hard that it is occasionally used as an automobile race course. Observation Techniques: Low oblique views using the 100-mm lens will show the lake and the surrounding mountain snowlines. Near-vertical views of the lake and lake shorelines using the 250-mm lens will enhance studies in the region by geologists, hydrologists, and state planners. Near-vertical photographs of the alluvial fans at the bases of surrounding mountains taken with the 250-mm lens can be used in studies of the relationships among deposition erosion, and recent faulting. No CIR coverage of Great Salt Lake or its basin exists: it may show many unexpected details of desert vegetation around and within the lake. Center point: 41°N, 112.5°W 95
