G.K. Gilbert and the changing Great Salt Lake

One of my favorite stories of early western water science is the clever way geologist G.K. Gilbert, in the 19th century, used the rise and fall of the Great Salt Lake as a proxy for decadal-scale climate variability. Here’s how I told the story inĀ my book:

G.K. Gilbert, courtesy Wikipedia

G.K. Gilbert, courtesy Wikipedia

The lake has no outlent, and so the only way water leaves is by evaporation, leaving its minerals behind. When the weather is wetter, the lake’s level rises. When it’s dry, the level falls.

Gilbert gathered stories from the Mormon settlers who had lived around the lake for decades. For years at a time, he found, the lake would rise. Then for years at a time, the lake would drop. Gilbert had found the first evidence for the years-long wet spells and dry periods that would shape the lives of the European immigrants trying to make a life in the arid land.

Today things are different. The sort of hydrologic stationarity Powell and Gilbert believed in is no longer a reasonable assumption because of the effect of climate change on both evaporation rates and precipitation patterns. In addition, human consumption has altered the flow of water into the Great Salt Lake. The result, according to this Salt Lake Tribune editorial, is a changed lake:

The Great Salt Lake is shrinking, taking vital wetlands with it. While the lake level historically rises and falls dramatically, warming temperatures and dwindling snowpack could mean a permanently smaller lake. If that happens, millions of birds and other wildlife could lose vital food, shelter and nesting areas.

The average lake level is 4,200 feet above sea level. The lake now stands at 4,196.5 feet; its lowest level was 4,191.35 feet in 1963. Then the lake covered only 950 square miles, a dramatic drop from its average of about 1,700 square miles.

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