Indiana Dunes National Lakeshore

The Land
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Thanks to the Ice Age, environments collided and deposited their remnants here at Indiana Dunes. The resulting strange combinations of neighboring plants attracted Cowles' interest.

Arctic bearberry grows next to prickly pear cactus, and southern dogwoods grow just over a dune from northern jack pines. Something else puzzled Cowles. Plant life differs dramatically from dune ridge to dune ridge. Plants growing near the lake front are not usually found farther inland, and inland trees cannot be found on dunes near the beach. He wondered why. Cowles observed that as plants grow on a site, they change it. When pioneer plants have changed the site sufficiently, the way is prepared for other plant species. New plants can now be more successful, so they crowd out the pioneers. Once marram grass becomes established on a dune, for example, that dune changes from an area with full sun to one with partial shade. As grass blades decompose, they build humus. Where there was only sand, now there is the beginning of soil. Change sets in. Cowles pieced together the puzzle and formulated basic ecological concepts.

These changes do not happen quickly. At the close of the Ice Age about 10,000 years ago, the landscape was covered with spruce and fir forests like those now found in Canada. As the climate warmed and glaciers melted to the north, the forests retreated. Some arctic plants, such as bearberry and jack pine, persisted, while plants forced south by the Ice Age reappeared.

Dry sand areas with minimal soil made homes for prickly pear cactus. Red oaks and sugar maples grew nearby in the deeper soil and humid conditions of protected areas.

Professor Henry Cowles found the Indiana Dunes and Lake Michigan shoreline a natural laboratory for developing important principles of plant succession. He arrived at the University of Chicago on a graduate fellowship in 1896 and retired as chairman of its botany department in 1934. He and his students conducted extensive field research in this region, and his dedication to deciphering its bewildering diversity of plant life led to the naming of Cowles Bog in his honor.

The curious landscape that caught Professor Cowles' inquiring eye is still here for you to explore. Ponds are scattered among younger dunes, which are closer to the lake. Marshes are found on old lake bottoms between long dune ridges. Sphagnum bogs, with their unusual environment and vegetation, are tucked in glacial moraine. These bogs and marshes, which are gradually filling with vegetation, will eventually become meadows, then forests.

Glacier Works

The landscape reveals natural processes at work here for millions of years. From the piles of rock and sand at Indiana Dunes, the geological story of the Great Lakes can be told in miniature. During the million and a half years of the Ice Age, massive sheets of ice crept southward across the continent in four waves. The last, called the Wisconsin Glacier, reached as far south as central Indiana. Following the bed of an ancient northward-flowing river, the mile-thick glacial lobe that would become Lake Michigan rested heavily upon the land. In its gradual advances and retreats over the eons, the glacier crushed all beneath it, scouring lake beds from river valleys and grinding rocks into pebbles. If you look at a map of North America and note the positions and dimensions of the Great Lakes, you may sense the powerful forces that created them. The glaciers' stupendous leveling and bulldozing effect may also become apparent as you explore the park.

The receding Wisconsin Glacier paused about 16,000 years ago near present-day Valparaiso and deposited rocks and soil of glacial till in a ridge of rolling hills called the Valparaiso Moraine. Between the moraine and the present shoreline of Lake Michigan is a series of similar lower ridges, further evidence of the glacier's remodeling activities. Stretching from the Valparaiso Moraine to the beach, these ridges of moraines and dunes mark the shores of a once larger lake that shrank by stages after the glaciers disappeared. You may not recognize such ridges today because they are concealed with vegetation, but beneath the veneer of plants and soil stretch massive sand piles just like those at today's lake front. Note that there are no mountains here, in the sense of the Rockies or Alleghenies, to interrupt the relative flatness of the Indiana Dunes area; all interruptions are deposits of sand or rock. As you drive through road cuts you see no massive bedrock to shape the land, only remnants of glacial moraines and former lake dune ridges.

As the glacier melted, plants colonized in its wake. The strange environment called Pinhook Bog was once part of this massive glacial system. Formed from an ice chunk marooned by the retreating glacier some 14,000 years ago, the bog is now filled with sphagnum moss and hosts unusual vegetation, from deciduous evergreens to insect-eating plants and delicate orchids. The shape of today's beach front is still changing, reminding us that the geological story of the Indiana Dunes National Lakeshore has no end.

Published: 29 Apr 2002 | Last Updated: 15 Sep 2010
Details mentioned in this article were accurate at the time of publication


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