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TEACH Shoreline Geology

3 | The sandy dunes

Sleeping Bear Dunes. Click for larger image. The sand dunes of the Great Lakes region represent the largest freshwater coastal dunes in the world. These dunes, such as the Sleeping Bear Dunes on the northeastern shore of Lake Michigan, are only 3,000-4,000 years old - that's very young, geologically speaking!

The Legend of the Sleeping Bear

How are dunes created?
Indiana Dunes. Click for larger image.Lake Michigan went through a stage of geological development where it was known as Lake Nipissing. Lake Nipissing's water levels were about 40 feet higher than they are today, creating many embayments at the openings of rivers. Eventually, sand from the rivers and currents created large sand bars that cut off the bays from the lake. Hamlin Lake in Michigan is an example of an inland lake that was once a bay in the Lake Nipissing time period. Lake Nipissing's water levels fluctuated greatly, much like Great Lakes' water levels do today; coupled with strong westerly winds, the sand bars were eventually sculpted into the towering dunes we see today.

Why are dunes important?
Piping Plover. Click for larger image. Sand dunes support a unique ecosystem, which develops in a succession, the process of one plant community replacing another over time. Pioneer grasses, such as marram grass and sand reed, "catch" blowing sand and help to build up the dune. Shrubs then take over the dune, such as red osier dogwood and sand cherry, and they stabilize the dune until trees are able to take root. Eventually, the dune will evolve into a forest. Dunes support a large habitat for native plants; the Indiana Dunes National Lakeshore ranks seventh among national parks in plant diversity!

Pitcher's Thistle. Click for larger image.Dunes are also the home for many endangered and threatened animals and plants. The piping plover, a small shorebird, nests in the shoreline sand, often in the protection of a perched dune. Houghton's goldenrod, pitcher's thistle, and the dwarf lake iris are all examples of threatened plant species that live on the Great Lakes dunes.

Are all dunes the same?
There are two types of dunes in the Great Lakes region: beach dunes and perched dunes. Beach dunes develop on the low-lying shores of Lake Michigan, and they consist mostly of sand. The Aral Dunes along Platte Bay on Lake Michigan are examples of beach dunes. Perched dunes, such as Sleeping Bear Dunes along Lake Michigan and the Grand Sable dunes along Lake Superior, sit on a plateau high above the shore. They consist of sand as well as other loose material, and dramatically changing lake levels help to create them.

What are the threats to dunes?
Dune mining. Click for larger image.

Sand is used to make molds for cars, trains, and airplanes as well as glass and concrete products. Dune mining destroys a dune, and the sand that is obtained is a nonrenewable supply; once a dune is mined, it cannot be replaced. The Sand Dune Protection and Management Act was passed in 1976, but the Great Lakes region continues to lose many of its dunes, such as Pigeon Hill, Maggie Thorpe, and Creeping Joe, to dune mining.

Dunes are also threatened by tourism. Golf courses are often developed on dunes. And climbing dunes causes excessive erosion, damages native and rare plants, and can destroy nesting habitats for birds and animals. When hiking on dunes, it's important to stay on the designated trails!

Find out what you can do to help save the dunes, and visit GLIN's Dunes page for more information.

Also visit BeachWatch, Delicate Dunes and Grass That Holds Its Ground

Graphics: Sleeping Bear Dunes; Indiana Dunes National Lakeshore; Piping Plover; Pitcher's Thistle; Dune mining

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