GVSU expert: A Q&A on what a dried-up, ancient lake in Utah can tell us about Lake Michigan

What led you and your team members to study Lake Bonneville? What were you hoping to learn?

Lake Bonneville is famous (as far as paleolakes go) because its remnant, the Great Salt Lake still exists, and because evidence like ancient shorelines is easy to spot in northern Utah. United States Geological Survey geologist G.K. Gilbert described the lake in detail as far back as 1890. For this project, we were working on a new geochemical tool called "triple oxygen isotopes" that had mostly been applied to the hydrology of modern waters, and so we wanted a well-studied lake to be among the first ancient applications of the technique. The modern Great Salt Lake is also in real danger of disappearing completely; therefore, data on how past climate changes affected this basin are also important.

Explain the characteristics of Lake Bonneville until it dried up and why its hydrology was similar to Lake Michigan.

Lake Bonneville was one of several large western U.S. lakes that grew during the last ice age, ultimately covering a roughly Lake Michigan-sized area of Utah by about 17,000 years ago. By measuring the geochemistry of fossil shells and rocks, we can now say that ancient Lake Bonneville and modern Lake Michigan had similar temperatures and similar relative amounts of inflow and evaporation. (A lake only exists if the amount of water flowing in is equal to or greater than the amount flowing out.) Standing on the shores of Lake Bonneville at its peak would have felt very similar to standing on the shore of Lake Michigan today.

What insight did you and other research team members take from this study on the long-term instability of these big bodies of water, such as Lake Bonneville and Lake Michigan?

Our work shows that cold ice-age era climate is what supported Lake Bonneville, not some major increase in precipitation. So, as the climate warmed out of the last ice age - much slower than climate change today - evaporation rates increased until ending up as the desert we see now. This is not good news for the modern Great Salt Lake, since climate change is exacerbating this trend toward warmer and more evaporative conditions.

The main lesson for the Great Lakes is that similar lakes have existed and then disappeared. Though it is hard to believe when standing on the shore of Lake Michigan and staring at the immensity of it, it too is likely to be a transient feature on a geologic time scale.

Remind us of how Lake Michigan was formed, what its arc has been, and how it has changed over time.

Lake Bonneville had largely dried up by the time the Great Lakes emerged. The basin holding Lake Michigan today was shaped by glaciers of the last ice age. That ice was melting in earnest by 10,000 years ago, both filling the basin and changing its shape as the crust rebounded from the great weight of ice being removed. As a result, different precursor lakes, both smaller and larger than the current shoreline, are thought to have formed, with differences in drainage as well. The modern shape where water flows under the Straits of Mackinac to the St. Lawrence river, rather than out via the Mississippi, may only be about 3,000 years old. In that sense, Lake Michigan is younger than the Pyramids.

What is the long-term outlook for Lake Michigan? Could it meet the same fate as Lake Bonneville?

Barring some purposeful diversion of water, there is no real concern that the Great Lakes will dry up anytime soon. So far, climate change has seemed to induce more severe swings in lake levels between record highs and lows, not a clear trend in either direction. But Lake Bonneville was of similar size and essentially identical temperature, hydrology and isotopic composition. And now Lake Bonneville is a mostly empty basin lined with salts. The lesson I think is not that the Great Lakes are in immediate danger of disappearing, but that big lakes do not tend to persist forever. It seems unlikely that Lake Michigan will retain its size and shape centuries from now, particularly as summers are quickly becoming increasingly hot and dry.