Terri of the Trails: The Great Marsh of the Indiana Dunes: The Backstory

near Beverly Shores, Indiana

The Great Marsh of the Indiana Dunes

The Backstory

May 23 and 24, 2013

The Indiana Dunes is such a fantastically diverse place. Here you can find Lake Michigan, sandy shore, dunes, swales, pine woods, hardwood forests, swamps, marshes, ponds, bogs, creeks, rivers and savanna. Sweeping off behind to the south is a large stretch of moraine, and behind that is the great land of savanna, sandy prairie and the Kankakee River valley wetlands, most of it now farmed. In the northern part, near the lake, all of this soup of ecosystems shares space with industry.

I grew up in this area. We played at the beach on summer days, climbed dunes, hiked trails, and walked along the lake shore. It is a place that is a strong part of my soul, and my heart leaps every time I see the view of sandy shore, rolling waves, and the blue-gray waters fading off into the sky, through an airy stand of Cottonwood trees, leaves fluttering in the lake breezes.

Even so, there is so much of it I didn't know.

Starting several years ago, Richard and I have taken our daughter and some of her friends here. Those were primarily “beach days” for the girls, though I would contemplate the design of pebbles washed up by the waves, and slip away now and then to observe the succession of plant life further back from the beach. Since then, Richard and I have been coming about twice a year, exploring more of the area, walking more of the trails, learning more about the array of ecosystems, and experiencing other seasons besides summer.

In May of this year, we focused on The Great Marsh and walked two trails that were new to us, in both the Indiana Dunes State Park and in the Indiana Dunes National Lakeshore areas.

“Great Marsh” is a misnomer, as one interpretive sign did point out. A marsh is a wetland dominated by herbaceous plants, mostly grasses, rushes, reeds and cat-tails. What we explored is really a swamp, which is a wetland where trees and shrubs are predominant. Both marshes and swamps have saturated soils. Marshes tend to be continually inundated with water, while swamps can be just partially or intermittently covered. But, the main difference is the matter of trees, which tend to be those species that don't mind having their feet wet all or most of the time.

Where is the Great Marsh (or Swamp) at the Indiana Dunes? It is a long stretch of swamp tucked between stretches of dunes, all running parallel to the lake shore.

This exhibit in the Indiana Dunes State Park Nature Center shows clearly how the swamp is situated between stretches of dunes (that little blue spot snugged in there). The dunal areas, starting just behind the beach, are a series of stages in the botanical landscape, referred to as “succession”. In the evolution of landscape, one stage succeeds another over time as more soil is created by the breakdown of plants from the previous stage, and conditions change. The last stage, called the “climax stage”, is the ultimate attainment, where the ecosystem maintains itself for a long period of time.

This is very clear to see at the Indiana Dunes.

In 1899, Henry Chandler Cowles (my hero!) developed and described this concept in his doctoral thesis, after studying the Indiana Dunes (more about him in a future blog).

So, how did a marsh (or swamp) get tucked in between two dunal succession stages? It doesn't fit in with the whole natural succession idea here. It seems to be an interesting anomaly.

It turns out that it got tucked in there between the fore and aft dunes as a result of changing lake levels, over thousands of years. The “aft” dunes are the oldest, and are referred to as “Calumet Beach”. This was formed after the last glacier receded and formed Lake Chicago. On the old Calumet Beach there now rests two roads that run parallel to the lake: Route 12 (which teeters on the edge between swamp and old beach) and US 20. Also seated on this old beach are towns such as Chesterton, Portage, Porter and Town of Pines – rather sandy places.

The lake level was higher when Calumet Beach was formed. As the level receded, Toleston Beach was formed, leaving water on either side. When lake levels rose again, waves pushed Toleston Beach further inland. The waves also created higher dunes on Toleston, which eventually became the present-day foredunes and beach. On Toleston Beach sits some towns whose names bespeak their location on or near the shores of Lake Michigan: Ogden Dunes, Dune Acres, Beverly Shores, Michigan City, and the industrial Burns Harbor.

looking west, with Burns Harbor in the distance

looking east, near Beverly Shores

This also created a lagoon between Calumet and Toleston beaches. When the water level in the lagoon dropped, water-loving plants could colonize it, other wildlife came in, and it developed as as great marsh (swamp). The historical succession, therefore, is: Lake Michigan, Toleston Beach (lakeshore and foredunes), Great Marsh (swamp), and Calumet Beach (older dunes). As the interpretive sign in the photo points out, the Great Marsh “...once extended from Gary to Michigan City”. Over the span of more modern history, humans drained a good part of the swamp for farming and development, as humans have been wont to do to such places.

But, nowadays, we appreciate the richness, diversity and ecological value of such ecosystems, just as they are. More of them are being preserved, and such has been the case with the remains of The Great Swamp at the Indiana Dunes.

Here is an interesting site to check out: http://www.geocaching.com/seek/cache_details.aspx?guid=82afc07b-ba9d-4e66-a20f-dca1b903c22b

I will be taking you on our two walks that we took in May, around and through The Great Marsh, in successive entries to this blog, to share our experiences. Sometime, I also will share with you the walk we took at Cowles Bog in early June of 2012. For now, here is a sampling of wildlife from The Great Marsh, in May: