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Great Lakes Article:

Time line shifts on sand dunes

Lake Michigan areas younger than thought

November 28, 2001

BY AMY E. NEVALA
Article courtesy of CHICAGO TRIBUNE

Lake Michigan sand dunes, long believed to have formed more than 5,000 years ago, appear to have a much younger and more complex history than previously thought.

For decades, geologists referred to the honey colored dunes hugging the shorelines as "old." Except for minor shifts in the dunes from waves and wind, they thought the most drastic changes in their formation had ended thousands of years ago.

Now researchers have found that in the past 500 years, wind, waves and human activity have reshaped the dunes. Instead of old, stable systems, parts of the dunes may be quite young and active, requiring a different approach in the way they are built on, mined and protected.

Although the history of the glaciers that carved the Great Lakes region is fairly well understood, much remains to be learned about the landscape since the ice left about 10,000 years ago, said Alan Arbogast, a geographer at Michigan State University who conducted the research.

"There's probably not going to be another glacier or Ice Age in our lifetime, so I want to know what's happening to our landscape today and how we play a part in changing it."

The 43-year-old scientist began his dune research three years ago, while examining a gutted dune in Grand Haven. A Kansas native who studied a sand prairie in the Great Plains for his graduate work, Arbogast was puzzled when he read assumptions about the age of the Lake Michigan dunes.

"It didn't seem to fit that they were old features that have been just sitting around for 5,000 years without changing much," he said. "Instead, our research shows that the dunes have changed frequently in the last 5,000 years."

Using a 100-foot dune in Van Buren State Park in South Haven as an example, Arbogast explained how he mapped the dunes' geologic history.

The dune, he said, started growing almost at lake level as blowing sand accumulated in clumps of beach grass, bushes and trees. As the vegetation died, more sand blew in and eventually piled dozens of feet high.

Another layer of vegetation grew and died on the new sand layer. The process repeated again and again and eventually, a sand dune evolved, with layers of black, decomposed vegetation.

By dating the layers of decomposed residue, Arbogast reconstructed the history of the dune.

"We have learned that this particular dune began to grow about 5,000 years ago and had distinct spurts of growth around 4,100, 3,500 and 2,000 years ago," he said.

Much remains to be discovered, Arbogast said. For reasons he still is studying, the Michigan dune stopped growing for about 1,500 years. Two additional growth spurts occurred in the past 500 years, the most recent 150 years ago.

With a few exceptions, Arbogast found similar histories among the dunes along the beaches of northwestern Michigan extending south to Indiana Dunes National Lakeshore.

The research builds on knowledge about what may be the world's largest accumulation of dunes around a body of freshwater.

The Great Lakes sand also has special qualities. Unlike the gypsum sand of New Mexico or the calcite sand in Bermuda, Great Lakes sand slips cleanly through the fingers, like silk.

Noted for its even-textured grain, the sand is made largely from quartz dumped by glaciers from Canada. Long after the ice departed, wind swept the sand grains together to form dunes as high as four-story buildings. The dunes mingle with grass and forests and stretch for miles along freshwater beaches.

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