Lake Bonneville

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Lake Bonneville and The Great Salt Lake

A Brief History

Lake Bonneville was a large inland lake that existed from about 32,000 to 14,000 years before present. It covered most of northwestern Utah including parts of Nevada and southern Idaho.
Lake Bonneville was formed due to the increased waters from melting glaciers. Also, the climate of the time is believed to be somewhat colder and wetter than it is today. Precipitation during Lake Bonneville time is suggested to be 33% more than present day with a basin temperature decrease of 13 degrees C, which would also lower the evaporation rate (Lemons 1996).
During the last 1 million years, the eccentricity variations in the Earth's orbit created glacial-interglacial cycles in 100,000 year periods. The Bonneville cycle is the last of these 100,000 year cycles recorded in the Great Basin (see graph below, from Currey 1984). In general, the periodic expansions and contractions of the great ice sheets in the high and mid-latitudes were accompanied by shifts in the main climatic zones of the low latitudes, and these produced marked spatial and temporal variations in regional rainfall values, seasonal distribution of rainfall, annual temperatures, and wind directions and strengths.
On a finer scale, research suggests that Lake Bonneville may have undergone major oscillations on a sesquimillennial scale (every 1500 years). Oviatt (1997) suggests that these lake-level fluctuations had amplitudes of about 50 m between 30,000 and 10,000 years before present and correspond to iceberg-rafting events, which took place in the North Atlantic Ocean. The lake level fluctuated due to changes in the size and shape of the Northern Hemisphere ice sheets, which deflected storm tracks into the Great Basin.
For a long period of history, Lake Bonneville was a terminal lake with no rivers draining from it. The lowest outlet for Lake Bonneville was Red Rock Pass in Idaho with and elevation of 5, 090 feet. A layer of hard rock in the pass stabilized the lake level for a long time, while the waves carved a fully developed shoreline complete with beaches and sand dunes called the Bonneville shoreline.
Water flowing through Red Rock Pass slowly eroded the resistant layer of rock and finally cut through it into a much softer formation beneath. The soft rock quickly washed out, abruptly lowering the elevation of the spillway by about 375 feet. During the next eight weeks, in an event called the Bonneville flood, about 375 feet of water drained off the top of Lake Bonneville through Red Rock Pass and into the Snake River.
Recent estimates place the maximum flow of the Bonneville flood at approximately 10,800,000 cubic feet per second. That is about 300 times the maximum flow ever recorded on the Snake River and six times the maximum on the Mississippi River.
When the spillway eroded to the next layer of hard rock, the lake level again stabilized, and the waves cut the Provo shoreline at about 4740 feet.
As the climate dried, and the lake level began to drop, Lake Bonneville no longer received enough water to maintain overflow through the spillway, and it slowly shriveled through evaporation to its last remnant, the Great Salt Lake.

Historic lake levels measured at the southern end of the lake.

Ancient lake levels interpolated from cores and other sources

Follow this link to a satellite image of the Great Salt Lake

Follow this link to a map of the Great Salt Lake and the surrounding areas

	Lake Bonneville	Great Salt Lake
Surface Elevation:	5,090 ft	4,200 ft
Length:	346 miles	75 miles
Width:	145 miles	30 miles
Surface Area:	19,750 sq. miles	2,000 sq. miles
Depth:	1,050 feet
Greatest Depth:		40 ft
Average Depth:		14 ft
High Elevation:		4212 ft (1987)
Low Elevation:		4193 ft (1963)
Remnants:	Great Salt Lake / Utah Lake

References

Kowalewska, Agata, and Cohen, Andrew S., 1998. Reconstruction of Paleoenvironments of the Great Salt Lake basin during the late Cenozoic. Journal of Paleolimnology. 20; 4, 381-407.

Lemons, David R., Milligan, Mark R., and Chan, Marjorie A., 1996. Paleoclimatic implications of late Pleistocene sediment yield rates for the Bonneville Basin, northern Utah. Paleogeography, Paleoclimatology, Paleoecology. 123; 1-4, 147-159.

Oviatt, Charles G., 1997. Lake Bonneville fluctuations and global climate change. Geology. 25; 2, 155-158.

Utah Geological Survey Website

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Last updated 9/20/01