High dunes arc Indiana's Lake Michigan shore

By Todd Thompson.

Feel the burn.

Mt. Baldy is the highest active dune along Indiana's Lake Michigan shoreline not far from South Bend. These drawings show how the Indiana Dunes and the Great Marsh developed over a period of 6,500 years. Graphics courtesy of the Indiana Geological Survey

I'm not talking about the sun on your shoulders but that muscle burn as you climb two steps forward and fall one back on the loose sand of Mt. Baldy. Mt. Baldy is one of the high dunes (100 feet or more) that arc along Indiana's Lake Michigan shore from just east of Michigan City to just west of Ogden Dunes. These active and relict dunes are some of the largest inland dunes in the world. As impressive as they are in height, they are equally impressive in that they primarily formed in only the last several thousand years.

Most of the dunes began forming about 6,000 years ago when the water in Lake Michigan was rising from an extreme low. The high dunes at that time were just a small ridge. Landward of this ridge was a broad lagoon where snails, clams, crayfish, fish (pike, garpike, bass, sunfish, walleye pike and loon), and an assortment of vegetation thrived. Because lake level was still rising, the small ridge was overtopped by storm waves and forced landward into the lagoon.

When the lake level stopped rising about 5,000 years ago, marram grass started to grow on the ridge. This grass captured sand blown across the ridge by wind. It is at this time that the first of the dunes began to form. These newly formed dunes coalesced and changed the character of the lagoon landward of them. Without the water from the lake coming in during storms, the lagoon turned into a series of ponds that would precipitate calcium carbonate and support calcium-carbonate-loving plants, such as muskgrass.

Between 4,500 and 3,500 years ago, lake level fell about 12 feet. The lower water exposed large quantities of sand that were generously blown into the high dunes we see today. Accompanying this rapid growth in dunes was a change in the lowland area landward of the dunes. The ponds dried up and many water-loving plants grew in this marshy area. Today, this lowland is still a wetland, known as the Great Marsh.

When visiting the dunes, you can ponder the development of the high dunes and the Great Marsh along many of the trails in the Indiana Dunes State Park, or you can tackle climbing Mt. Baldy in the Indiana Dunes National Lakeshore.

This trip to the dunes is brought to you by the Indiana Geological Survey; visit its Web site at:

http://www.indiana.edu/~igs

For information about the park, visit the National Park Service's Indiana Dunes Web site at:

http://www.nps.gov/indu/

Return to Table of Contents