A Brief History of Glaciation in Wisconsin
- Jason G. Freund
- 3 days ago
- 8 min read
This post follows a previous post on the bedrock geology of Wisconsin.
Glaciation defines much of the geography of Wisconsin. Other than the Driftless Area - and even some of what we often call the Driftless Area - is covered with "glacial drift". Drift is simply material moved by glaciers. In this post, you will not see many references to the Driftless Area. Instead we will concentrate on the glacial features of the state. Glaciers are responsible for much of the state's landscape and nearly all of its lakes. No event has had a great influence on the state's geography.
First, a bit of context. We are in an Ice Age, the Quaternary Glaciation, but are currently in an interglacial period. The glacial periods, quite simply, are periods of colder air temperatures where glaciers cover a larger portion of the Earth. We, of course, still have glaciers - the slideshow of images above are from the South Island of New Zealand. But there and elsewhere, glaciers are retreating fast. Go see them while you still can! The last glacial period ended about 15,000 years ago. In North America, we refer to it as the Wisconsin glaciation; in other countries, they have named it for where its evidence is best preserved. The next glacial period is expected to be in about 50,000 years, but greenhouse gases may delay it by another 50,000 years (André Berger).
The figure above is an approximation of where glaciers have been, and still are, in the Northern Hemisphere. Much less of the Southern Hemisphere has been glaciated - there is also much less land mass south of the Equator.
History of Glaciation in Wisconsin
Parts of Wisconsin have been glaciated at least four times, but older glaciations are difficult to see evidence of these older glaciations as that evidence has been carved away and/or buried by more recent glaciations or by water. There have been at least five ice ages, probably more, but evidence of those before our current ice age are rarely seen on the landscape.
The Wisconsin Glaciation was the most recent one but, as you can see from the figure above, other parts of Wisconsin were covered by earlier glaciers. The Wisconsin Glaciation has eroded or deposited drift over past glaciations. Below is a more detailed view of these glaciations.
The figure above shows a more detailed view of the Wisconsin Glaciation. You will notice that the most recent glaciation did not extend as far as some of the previous glaciations. And the terminal moraine - labeled with the question marks - is not entirely visible on the surface anymore. As you can see, part of the "Driftless Area" nearest to the Mississippi River is not truly driftless. You will also see a number of moraines - formed at glacial margins - formed as the Wisconsin Glaciation retreated.
Lastly, this figure shows us how deeply bedrock is buried. In much of the state, bedrock is buried quite deeply, which is evidence of glaciation. For a more detailed view of the Quaternary geology of Wisconsin, download this map from the Wisconsin Geologic and Natural History Survey and for a 3D map of the state, UW Extension.
Glacial Landforms
Glacial features and landforms can be categorized as erosional and depositional. Erosional features are caused by the removal of materials by glaciers (i.e. U-shaped valleys, Fjords) and other evidence of the glaciers such as striations on bedrock. Depositional landscapes are more pronounced in Wisconsin. Examples are the morianes, drumlins, kames, eskers, and the many kettle lakes that are created as blocks of ice are left behind as the glaciers retreated.
Moraines
Moraines are formed in a number of different ways which makes a number of different types of moraines. The most obvious moraines are generally terminal moraines which are formed at the end of the glacier. The most obvious of these is the Johnstown Moraine which is evident from Rock County north to Langlade County. It is the moraine that is dammed the valley that Devils Lake is in. The Kettle Moraine is the other moraine the other moraine most are familiar with. It is an interlobate moraine, occurring where the Green Bay and Lake Michigan lobes of the Wisconsin Glacier came together. As the name suggests, this moraine is filled with kettles, created in outwash plains by chunks of ice that melted and left a depression in their place. Many lakes in Wisconsin fill these kettles, but kettles in higher elevations are often dry or seasonal wetlands.
Landscapes of Dane County (Wisconsin Geological and Natural History Survey)
Deposition of the late Wisconsin Johnstown moraine, south-central Wisconsin (US Geological Survey)
Pleistocene geology of the Steinke Basin area of Devils Lake State Park
Video - Tutorial on the formation of a Terminal Moraine - A. Wylie
Drumlins
Drumlins are elongate hills whose direction are indicators of the direction of ice flow during glaciation. We do not exactly know how they are formed, but we have a couple of theories. They often occur in drumlin fields or swarms - including a few places in Wisconsin. Wisconsin has over 5,000 drumlins (source). Some examples of Drumlin fields around Campbellsport, Goose Lake, and near my hometown of Waterloo.
Kames
Kames are conical shaped hills that are formed by meltwater. Wisconsin has a number of "moulin kames" which are sand and gravel hills created by meltwater holes in glaciers. These are quite a bit less common than are drumlins. One of the best places to see kames is from the Parnell Tower near Plymouth, Wisconsin.
Esker
Another name for eskers is "serpentine kame" which gives a bit of insight into what they are. Eskers are formed in melwater channels under glaciers. They are essentially rivers flow under glaciers that are preserved on the landscape today. They can also form from glacial rivers on the tops of glaciers. Their riverine formation is what results in their serpentine shape. There are relatively few eskers in Wisconsin, but they are very common in places like northern Canada and Michigan, which has over 1,000 eskers. A few examples in Wisconsin are the Parnell Esker, Mondeaux Esker, Lost Lake Esker, Cable Esker, and Hospital Esker near St. Croix Falls, probably the state's tallest esker.
Lakes
Probably the feature most associated with glaciers are lakes. Unglaciated West Virginia had one natural lake, created by a sink hole, that recently dried up. Here in Wisconsin, we have about 15,000 lakes and nearly 6,000 lakes over 10 acres in size - the minimum set by Minnesota in their count of 10,000 lakes (11,842 officially). The northern highlands lake district in Vilas County and surrounding counties is one of the largest concentrations of lakes in the world. As you probably know, there are few lakes in the Driftless Area, and most of those are oxbow lakes of the area's larger rivers and not glacial lakes.
Glaciers create lakes through erosion, deposition, and damming. The Great Lakes were created by glacial scouring which then filled with meltwater as the Wisconsin Glacier retreated. Other examples of Wisconsin lakes created by erosion are the Madison / Yahara chain of lake and many northern Wisconsin lakes. Many of Wisconsin's lakes were formed as large volumes of ice melted within the outwash plains, leaving behind kettle lakes. These, as the name implies, tend to be near circular lakes whereas erosional lakes tend to be more elongate (but this is a generality). Examples of kettle lakes abound in Wisconsin - some of the best examples exist in the Kettle Moraine area such as Mauthe Lake but they are common in northern Wisconsin as well. Lastly, a number of dammed lakes were created as either moraines or ice blocked the flow of water, resulting in lakes. Examples of dammed lakes in Wisconsin are Lake Winnebago, Devil's Lake, and the Horicon Marsh, which was a shallow lake before man had its way with the marsh.
Ice Age Trail
The Ice Age Trail is a great way to see glacial features of the state, I mean, that is why the trail was created. It largely follows the moraines of the Wisconsin Glaciation. The trail is about 1,200 miles and would take 2-3 months to "thru hike". However, there are many day hikes that are quite nice - I've done a number of them. The best developed sections are on public lands and many segments are not yet complete. There are many great resources to learn more about the trail and its over 100 segments.
Obligatory Fly Fishing Content
Because this is a fly fishing blog, I feel obligated to include some fish content. While certainly the Driftless Area is known as "trout central" in Wisconsin, the rest of the state is also loaded with trout streams. In fact, the highest density of trout streams occurs in Marinette County, in Wisconsin's far northeast. And a quick look at the map for Marinette County shows how the western edge - along a moraine - is where most of these streams originate. Overlay the Ice Age Trail map on the one below and you will see a good bit of overlap.
A number of glacial features stand out in this map, in particular the influence of the moraines and other glacial features. Nelson Hamm - a real geologist, not a wannabe like me - gave a great talk about how channels through moraines sorted glacial till and were responsible for large springs like Mecan Springs. I don't understand the nuances of the features of moraines or outwash plains and how they influence groundwater flow - but I know they do!
And it is not just about trout, there are many great warmwater rivers and lakes that provide great fishing. Look for an upcoming series of posts on the geographic regions of Wisconsin and fly fishing opportunities within each of them.