send
Send Letter to Editor

Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

suplogo.jpg - 11922 Bytes


The beautiful and bright Carolina Puccoon is among many unique plants found living in dunes in Wisconsin.© Kevin Collison.
7c.jpg - 20892 Bytes

June 2004

A geological wonder

Dunes, spits and swales.

Natasha Kassulke


The bright Carolina Puccoon is among many unique plants found living in dunes in Wisconsin.

© Kevin Collison

Contents
A beach is born

Heather Kelley doesn't like to play favorites, but admits a fondness for Seagull Bar State Natural Area in Marinette.

"It isn't developed and is still wild," she says. "It's an important beach for shoreland and migratory birds."

Two years ago, Kelley, a BEACH Act geographic information system coordinator for the Wisconsin Department of Natural Resources, was part of a team that traveled Wisconsin Great Lakes coast to identify and map public beaches.

The EPA uses this mileage beach to allocate funding for water quality monitoring and education.

Sixty public Great Lakes beaches were referenced in literature and online. By project completion, the team had found 190 public beaches of varying geologic formation and accessibility – some reachable only by boat. Each beach was mapped and over 100 are being monitored.

"The results surprised a lot of people," Kelley says. "Many of the public beaches were not posted as public. Beaches aren't all sandy, white and pristine. Some are comprised of gravel and/or larger rocks."

The beaches also vary in size. Some are more than a mile long. Others are small sandy spaces next to boat ramps. Door County had the most beaches by virtue of having the most shoreline.

"We've now extensively mapped 56 miles of public beaches and we're focusing our monitoring in those areas," Kelley says.

Using GPS (global positioning system), GIS (electronic mapping), aerial photos and parcel data, Kelley delineated beach size and indicated where public beaches started and private property stopped.

A beach is born

The sand your feet sink into today, is largely the product of glaciers that covered the Great Lakes basin over one million years ago. Wind, waves and erosion work in concert to produce beaches of varying size and shape. Beach color varies according to the sand's mineral content.

Beach formation begins as eroded material – sand, gravel and rocks – deposited on shore by waves. The continual onshore-offshore movement of waves and tides gradually pushes the sand along the beach edge.

"Wisconsin beaches are comprised of sediment from glacial deposits, limestone, sandstone and granite," Kelley says.

Among the beach types Kelley discovered were sand spits, rocky beaches, beach ridges, barrier beaches with lagoons, sand dunes and urban beaches.

Sand spits

Sand spits are found at Long Tail Beach in Brown County and Seagull Bar in Marinette County. These beaches feature long sandy stretches continuing into the water even where the shore ends.

Long Tail Beach on the west shore of lower Green Bay is a narrow sand spit. The size and shape of the peninsula combined with fluctuating water levels result in diverse wetland plants and animals. During high water time the point becomes a series of small islands.

Black willow and cottonwood are found on high ground, grading to reed grass and marsh dominated by cattails and bulrush. A sedge meadow houses bluejoint grass and cattails. Invasive exotics such as purple loosestrife threaten native species here. There is a sandy beach along the point's east side.

Erosion from dredging and poor water quality in Green Bay has destroyed some wetlands, but this site still provides important habitat for shore birds, gulls and terns. It is an important migratory bird stopover.

Seagull Bar at the mouth of the Menominee River on the margin of Green Bay features a shallow bay with marsh vegetation that expands or recedes with lake level changes. The eastern edge of Seagull Bar forms sand beach ridges and low dunes.

The dunes support marram grass, Canada rye, beach pea, and several rush species in low, wetter areas. In spring and fall, shorebirds by the thousands congregate at the sand beach. The federally endangered piping plover has attempted to nest here in recent years. Seagull Bar was designated a state natural area in 1962.

Rocky beaches

Schoolhouse Beach in Door County on Washington Island is one of Wisconsin's great rocky beaches. The beach is named for the log schoolhouse built there in 1850. The beach is comprised of large round and smooth stones.

Local laws prohibit taking the rare rocks, but this is the place if you like to skip rocks.

Ridges and swales

Baileys Harbor Ridges in Door County is on the eastern edge of the Door Peninsula on Lake Michigan. The peninsula features a ridge of dolomite limestone, which is part of the Niagara Escarpment that passes through east central Wisconsin. Much of this area is made up of low, sandy ridges, alternating with wet areas called swales.

The ridges parallel the shore and extend inland about a mile. Spring wildflowers – hepatica, trilliums and trout lilies – bloom from mid-April to the end of May. The sanctuary's symbol is the showy and rare lady-slipper orchid. Twelve endangered or threatened plant species are protected within the sanctuary.

Beach ridge formation at The Ridges Sanctuary started 1,200 years ago when Lake Michigan extended a mile farther inland than it does today. Sand deposited during the last glacial advance was carried by longshore currents and slowed by the shallow U-shaped harbor.

Fluctuating water level is another important ridge former. When lake levels are high, waves push the sand into a low ridge along the shoreline. As lake levels drop, the ridge is exposed and sometimes capped by wind-blown sand. One by one, the ridges form.

Plants stabilize each new ridge – first sedges and grasses, followed by shrubs and a few tree species. Gradually other trees and plants move in, finally becoming a boreal forest.

About 30 crescent-shaped ridges of sand and soil have formed parallel to the shore. The ridges closest to the shoreline are the youngest. Since it takes 30 to 40 years for each ridge to form, older plant communities are found on each succeeding ridge.

Point Beach Ridges is another such beach, located within Point Beach State Forest in Manitowoc. It has 11 ridges and swales paralleling Lake Michigan that formed through the protracted lowering of glacial Lake Nippisson. The ridges and swales are actually old beaches deposited during the last 8,000 years.

Except for a strip of dunes and beach along the lake, the area is forested. The beach harbors several uncommon plants including dune thistle, clustered broom-rape, thick-spike wheatgrass, prairie sand-reed and dune goldenrod, which all are state-threatened. The endangered sand dune willow is found here at its only known Wisconsin location.

Barrier beaches

Barrier beaches feature sand in front of lagoons. Examples include the Big Bay State Park and Big Bay Town Park on Madeline Island in Ashland County.

The state's 2,350-acre state park houses sandstone bluffs and caves. Bird watchers are intrigued to find that 240 bird species use the park. At Big Bay Town Park, a wooden footbridge crossing the scenic lagoon is popular for canoeing and fishing.

Coastal fen, coastal bog, shrub swamp and tamarack swamp border the lagoon. A floating mat around the lagoon is composed of native sedges, sweet gale and buckbean. Further away, a coastal bog mat consists of sphagnum mosses, shrubs and sedges.

Sand dune areas

Great Lakes sand dunes comprise the most extensive freshwater dunes in the world – so large they are visible to astronauts in outer space.

Here the piping plover nests in shoreline sand. Houghton's goldenrod, pitcher's thistle and the dwarf lake iris are threatened plants that thrive in Great Lakes dunes, according to the Wisconsin State Herbarium.

Whitefish Dunes State Park in Door County is Wisconsin's best example of a large sand dune area. Established in 1967, this 865-acre park has a three-mile shoreline, composed of sandy shoreline and rocky bluffs. Exposed dolostone is a clue that a shallow warm sea once covered the area 425 million years ago during a period known as the Silurian Sea. Fossils and seashells are exposed here and in rock throughout the Door Peninsula.

Push a magnet into the sand, and magnetite, an iron mineral found in the Lake Superior basin, will cling to it. These sand grains are debris that glaciers eroded from the bedrock of Canada and dumped into Lake Michigan.

The beach at Whitefish Dunes State Park is constantly reshaped by wind. Wind blowing over Lake Michigan hits the shore hard, picking up sand grains and pushing them inland. As the wind velocity slows over land, sand drops to the earth, and in time a pile forms.

These piles grow into dunes. Once cresting the top, the wind moves down the steeply sloping backside, which creates momentum to pick up sand grains and continue inland. The wind speed slows again as it heads inland, sand drops to the ground and the process starts over. Younger dunes block the wind and allow plants to establish on the older dunes. These plants live and die over hundreds of years, creating sandy soil.

Wind-formed dunes consist of medium to fine sand grains. As the wind blows, a process called "saltation" moves the majority of the sand. Saltation is a bouncing of the grains across the beach. Coarse sand is too large to be moved by this process and moves short distances by rolling along the surface. Fine silt particles are carried in suspension by the wind for long distances.

Between the water's edge and dunes' beginning, dry sand is constantly in motion, which makes it a tough place for plants to root. One kind of plant that does live here is marram grass. Its roots spread just under the sand surface to form an underground web that helps hold the sand in place. Though marram grass stabilizes the sand for its own survival, as a side effect other vegetation can take hold.

Frogs and toads, turtles, and snakes live here too.

Kohler-Andrae State Park in Sheboygan County also features sand dunes, miles of beach and rich maritime history. Over 50 vessels have sunk in this area alone, including an 87-foot schooner the Challenge built in Manitowoc in 1852. In 1982 a section of this ship's keel washed ashore at Kohler-Andrae and is now on display outside the Sanderling Nature Center.

Some Great Lakes dunes are threatened by mining. Sand is used to make foundry molds for cars, trains and airplanes as well as glass and concrete products. The Sand Dune Protection and Management Act was passed in 1976, but the Great Lakes region continues to lose dunes.

Urban beaches

In cities, beaches are a respite from pavement and offer free or cheap family recreation.

Bradford Beach on Lincoln Memorial Drive in Milwaukee is the city's most popular beach for swimming and sunbathing. Amenities include sand volleyball courts, a bathhouse and concession buildings. Water temperatures fluctuate from the 50s to upper 60s throughout summer and on a warm weekend day, 900 to 1,500 people enjoy the beach.

Deland Park Beach located on Lake Michigan in downtown Sheboygan is another popular urban beach and offers a bathhouse, shelters, public boat launch and is the home of the Sheboygan Yacht Club and Youth Sailing Center.

Natasha Kassulke is associate editor of the Wisconsin Natural Resources magazine.