Wednesday, February 22, 2012

Ode to the Glaciers

What do you love most about Northern Wisconsin? Rolling hills traversed by some of the best trails in the country, winding back roads, sparkling lakes, and shady green forests are some of my favorite features. Have you ever wondered why all these wonderful things come together in Northern Wisconsin? Maybe you know that this region was shaped by glaciers, but have you ever really sat down and appreciated all that the glaciers did for us?

I love glaciers. I have never seen one in person, and yet they have vastly improved my quality of life. Whether you realize it or not, you also know the joys of glaciers whenever you whiz down a rolling ski trail, hike merrily up and down hills, enjoy the stomach-dropping exhilaration of catching air on your snowmobile, or boat and fish on one of Wisconsin’s more than 10,000 lakes.

The landscape around Cable and Hayward was shaped during the Wisconsin Glaciation (named for us!) of the Quaternary Ice Age (which is still going on in Greenland and Antarctica). It began about 100,000 years ago, hit its maximum extent about 21,000 years ago, and the last glacier had retreated out of Wisconsin into Canada by 10,000 years ago.

The very recent (geologically speaking) visit of a glacier here has had a profound impact on what the landscape looks like. As glaciers advanced across the land they scraped and carved and plucked up rocks from their path, and carried them along within the ice mass. Like a conveyor belt, they brought tons (literally) of sediment south with them. Two lobes of ice flowed into our area, and their lateral margins met somewhere near Cable.

Where we really start to get interested is when the climate warmed and the ice began to melt faster here at its toe than new snow from Canada could replenish it.  Huge chunks of ice were left behind from the melting edges of the glacier, and then glacial outwash rivers carrying meltwater and debris off the glacier buried those ice cubes.  Well-insulated, the ice lay hidden under a flat surface of sand, gravel and cobbles for many years.

As the ice melted, basins of all shapes and sizes were left behind where the ice had been. Sometimes these basins, called kettles, filled with water and became lakes, others are perched far above the water table and stay bone-dry. The landscape of sandy, rocky soil pockmarked by kettles is called a “pitted outwash plain.” The Rock Lake ski and mountain bike trails east of Cable are a prime example of this topography, and in my opinion, a prime place for recreation because of it. The Birkie Trail takes advantage of the varied topography so much that its hills are legendary.

In places, the glacial conveyor belt stagnated for a while, leaving a line of jumbled sediment where its margin had been.  This is probably what created the wacky shoreline of Lake Namakagon – with many shallow bays and great fish habitat.

Even the towering spectacle of Mount Telemark owes its existence to the glaciers – rivers flowing on top of the melting ice carried rocks into a large crevasse.  When the glacier melted, a 1,700-foot-tall pile of sand called a “kame” was left behind. It is the tallest kame in Wisconsin.

Not only did the glaciers shape the physical landscape, they, by extension, continue to impact the human uses of it.  Unlike regions to the south and north, we don’t have extensive farming.  Not only are there too many hills, but the soil just keeps growing more rocks. First, water to percolates underneath buried rocks. When it freezes, the ice crystals lift up the bigger rocks and sand falls underneath. Over many freeze-thaw cycles, the rocks come to surface, right in your carrot patch! Happily, many trees grow just fine in this type of soil, so our local crops are forests instead of corn.

The next time you’re out for a spin on a lake, road or trail in Northern Wisconsin, take a moment to appreciate the wonderful legacy of the glaciers.

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