Time line shifts on sand dunes
Lake Michigan areas younger than
November 28, 2001
BY AMY E. NEVALA
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
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
"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
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
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
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
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