| The most recent period of glaciation, the Wisconsin Glaciation, gradually ended approximately 10,000 years ago. The glaciers of this period covered a large portion of the state under a mile of ice and snow. The advancing ice was split by upland areas into six different lobes. The St. Croix basin was transformed by the Superior and Chippewa Lobes. Slowly the frozen landscape retreated leaving behind a varied and unique landscape. We are fortunate to have many types of landforms crafted by glaciers that are among the most outstanding examples in the world. Normally when we think of glacier topography we think of the Kettle Moraine and Wisconsin Dells, but the St. Croix basin has many examples well worth checking out. | |
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One of the best ways to view the glacier’s remains is the Ice Age Trail which follows the edge of the Wisconsin Glaciation. The trail when completed will be a twelve-hundred mile national and state scenic trail located entirely in Wisconsin. It will be one of only eight national scenic trails in the United States. The purpose of the Trail is to tell the story of the Ice Age and continental glaciation along a scenic footpath. Approximately 600 miles of the trail are already completed. Within the St. Croix Basin the Ice Age Trail travels through Barron, Burnett, Polk, and Washburn counties. The Ice Age Park and Trail Foundation is one agency that oversees the entire trail. See the Ice Age Trail website for more information about the trail. Beginning in Barron County, the northern and western parts of the county are studded with end moraines, and a lake-rich zone dominated by steep kettle topography. The Blue Hills, a 1.6 billion-year-old quartzite range begins in the eastern portion of the county and continues through Rusk and Sawyer Counties. Between the moraines and the Blue Hills is an outwash plain created by meltwater from the Chippewa and Superior lobes. |
 Ice Age Deposits found in the St. Croix Basin. Illustration credit: UWEX |
Washburn County has good examples of medial
moraines created in the area where the Superior and
Chippewa lobes met. The rest
of the county is dominated by hummocky,
lake-studded outwash plain
and steep kettle topography.
The Northern portions of Bayfield and Douglas County were under Glacial Lake Superior. Immediately south of Glacial Lake Superior is an area of medial, lateral and end moraines. The southern part of the counties is an area of outwash plain. Western Polk and Burnett counties are underlain by a type of volcanic rock call basalt. This blackish rock is exposed throughout the St. Croix River Valley. The basalt bluffs and exposures are estimated to be 1.1billion years old. Polk County has some of the showiest features in the basin. In St. Croix Falls you can find the scenic St. Croix Dalles. In the north central portion of the county is the Straight River, considered to be one of the best examples of a tunnel channel and esker system found anywhere. Throughout the counties are examples of erratics or boulders carried and deposited by the glaciers. These out of place boulders can have origins from as far away as Canada. |
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Most of St. Croix and Pierce counties were sculpted during two prior glaciations. Not a great deal is known about these glaciations. It is estimated that the first period was probably between 2,400,000 and 790,000 years ago and the second is estimated to have occurred between 790,000 and 25,000 years ago. For more information and maps describing Wisconsin’s glacier past check out the Wisconsin Geological and Natural History Survey. |
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 Photo Credit: Ice Age Trail |
Dells/Dalles - A gorge cut by the torrents of meltwater released by the melting glacier or the draining of glacial lakes. These flows cut spectacular gorges in several areas of the state. The best examples are the Dells of the Eau Claire, the Wisconsin Dells, and the Dalles of the St. Croix. the photo to the right is the Western Terminus of the Ice Age Trail overlooking the Dalles of the St. Croix in Polk County. |
 Photo Credit: UWEX |
Erratics - Boulders transported from their origin by a glacier, so that they are now found far from their parent rock and are now isolated amid dissimilar materials. Erratics found in Wisconsin have been transported from as far away as Minnesota, Michigan and Canada. The photo to the Left is an example of an erratic found in the basin. Their sizes can vary greatly. |
 Illustration Credit: UWEX (Roll your mouse over illustration to see animation) |
Esker
- A long sinuous ridge composed of sand
and gravel deposited by the streams that flowed through tunnels
at the base of the melting glaciers. Notable eskers are found in
Polk and Taylor counties. Roll your mouse over the illustration
to the left to see an esker grow.
Photo Credit: UWEX |
.jpg) Photo Credit: Ice Age Trail |
Hummocky - Hilly, knob-and-kettle topography created by melting ice under glacial till. The photo to the left is Jerry Lake found along the Ice Age Trail. |
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Kettles
- Kettles are an example of inverted
topography. Occasionally the flow of the glacier stopped and stagnating
ice would break and become buried in the glacial till. As the
ice melted, the till material collapsed into the hole forming
funnel shaped hollows, 20 feet or more deep. Many of Wisconsin’s
lakes lie in the depressions formed by the melting of buried ice.
Roll your mouse over the illustration to the left to see how a
kettle is formed. Below is a photo of an area kettle lake in Barron
County and its lake depth map in ten foot intervals. The 22 acre
lake has a maximum depth of 47 feet. |
 Illustration Credit: UWEX |
Lobe - A tongue-like extension of an ice sheet. Portions of Wisconsin were covered by six major lobes during the late Wisconsin Glaciation, the Superior, Chippewa, Wisconsin Valley, Langlade, Green Bay and Lake Michigan. |
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Moraines - There are three different types of moraines, end (or terminal), medial and lateral. When the ice melted at the edges of the lobes, the sand, silt, cobbles, and boulders frozen in it were released and formed ridges called moraines. The moraines of the north form a broad band of hills and hollows dotted with lakes, marshes and bogs. Some moraines stand no more than 30 feet above the surrounding terrain, but other such as in the Kettle Moraine rise to heights of 250 to 300 feet. The end or terminal moraine is a type of moraine formed at the outer edge of the maximum extent of a glacier or glacial lobe. The medial moraine was created where glaciers or glacial lobes met and lateral moraines are found along the sides of the glaciers of glacial lobes. Roll your mouse over the illustration to the left to see the different types of moraines. |
 Photo Credit: Gary Dunsmoor |
Outwash Plain - A sandy plain formed when glacial meltwater streams in front of the glaciers spread over a very wide, flat area. Sand was swept along into both glaciated and unglaciated areas by the water. The photo to the left is an example of outwash plains found in the northern part of the Northwest Sands Area in Washburn County. |
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Tunnel Channel - Glacial meltwater under extreme pressure flowing beneath the surface of the retreating glacier blasts out a channel as the water moved toward the glacier’s margin. After the glacier has melted, the valley often contains a series of lakes. The Straight River in Polk County, pictured to the left, is likely the finest example of its kind found in the Midwest. |
