Lake Katherine: Of Kettles and Ice
It’s mid-January and we are just about to have our first cold snap of the winter. Yes, there have been a few days earlier this season that pushed the mercury down, but we haven’t had one of those true ice-makers of a week or even a few days. The coming forecast over the Martin Luther King Day weekend is for highs in the single digits and nights below zero. While that will cause everyone’s furnaces and wood stoves to run more continuously, it’s more like winter and the kind of cold we need to let the lake rest.
My wife, Donna, and I have been out on the lake cross-country skiing during the last week, and before that, she was ice-skating. The lack of snow was frustrating, but once the nights got below freezing on a routine basis, the lake “made ice” and it was smooth and safe enough for skating for a week or so. Then, light snow occurred for several days in a row rendering ice skating not easy, but skiing possible.
There is a saying that “lakes slow down water” (in comparison to rivers and streams). That’s true, but ice really slows it down, locking up the water molecules in crystalline form. Ice is good for northern lakes, large and small. Ice acts as a reflector to sunlight allowing the lake to cool down. It also prevents evaporation so that lake levels stay essentially stationary.
For northern lakes like Lake Katherine, ice cover drives the timing of the warming of the surface layer in the spring after ice-out. A few years back, the ice went out in early April. Other years, the ice has stayed on the lake until after the fishing opening weekend had come and gone. In the spring after ice-out, the top layer starts to become oxygenated and warmer until the water temperature at the top and bottom of the lake equalizes. Then, the lake “turns over" and oxygen from the top and bottom layers of the lake mix, and nutrients trapped at the lake bottom are released, freely moving about the lake. This supports plant growth (think algae mostly), which is the base of the food web in the lake allowing the lake to have a thriving fishery.
Reduced winter ice cover can lead to greater lake warming during the ice-free season. Lake Katherine as a northern spring-fed lake is considered cold as anyone swimming in it is well aware. Much as we might like a little warmer water in the summer, water temperatures going in fall determine the magnitude of evaporation from the lake surface. Warmer water temperatures result in greater evaporation and that can have a pronounced effect on lake levels especially if we have a dry fall as we did in 2023. Lake levels dropped a good deal because of that.
The amount of snow falling after ice first forms also affects the amount of ice. Because snow is a good insulator, if there is a lot of snow on a relatively thin ice sheet, even plunging temperatures will not cause a great deal of additional ice to be made. We’ll have to see if the coming cold snap makes much more ice. The amount of snow on the lake currently is probably two to three inches on average.
Ice has a long history in northern Wisconsin. The gigantic glaciers have come and gone multiple times over the last several million years. The most recent ice age started around 35,000 years ago and ended around 11,000 years back. During that time, ice sheets a mile or more thick ground over the landscape resulting in the landforms we see today including the Great Lakes and the thousands of lakes in sand/gravel dominated part of the state where Lake Katherine exists - the Northern Highlands.
As the glacial lobes retreated, large and small pieces of ice fell off, many of them became buried under gravel that was carried and pushed around by the glacier. Over time, these ice blocks melted and the soil over them collapsed. If there was enough water in the ice and if groundwater through springs brought additional water to the collapsed area, a lake was formed. These kinds of lakes are called “kettles”and are typically roundish in shape. It is not clear that Lake Katherine is a true “kettle lake” as it is topographically a complex lake with multiple bays. However, the lake could be the combination of several smaller kettles that eventually became connected by the groundwater level. The steep sides around much of the lake and similarly deep drop-offs in many places support this idea, but we might need a professional limnologist or geologist to confirm that or not.
The surrounding higher ground has additional evidence of kettle formations being common in this area. I have seen from my walks in the woods, particularly on some of the tracts now owned and managed by the Northwoods Land Trust, large and small “potholes” that have the shape of a funnel without the narrow tube at the base. These would have been created by smaller pieces of ice broken off the retreating glacier and again covered by gravel and eventually melting causing the collapse of the ground above. Their placement on high ground well above the groundwater level has left them dry. The area on both the east and west side of the eastern part of the lake have several dozen recognizable dry “kettles.” One of them is quite evident and visible just off Miller Lake Road where the recent timber harvest on NWLT land occurred. There are a half dozen or so on the NWLT tracts on the west side of Highway 51 near the wayside. A Lidar (a remote sensing method used to examine the surface of the Earth) image that I was able to download clearly shows these kettles in an arc on the NWLT tracts and there are a couple of what appear to be very large kettle features just to the west on private land on the north side of Lee Lake, which itself is probably a kettle lake and prior to the construction of the Bearskin Trail railroad grade was “attached” to Lake Katherine by a small wetland..
This contemporary LIDAR imagery reveals the finest scale elevational changes. You can see the “kettles” in a line in the “SESE” section as well as a couple in the “GL01” section below it.
Our changing climate is creating greater variability in weather patterns in ways we do not yet completely understand nor can we accurately predict. The variability at global scales over long time periods tens of thousands of years ago brought enormous amounts of ice to this area and created what we have today. The coming variability will affect ice at a more micro scale as winters start later, end earlier, and perhaps leads to changes in ice cover on our lakes, which in turn will have a cascading effect on the ecology of the lake and the values we as lakeshore owners and stewards enjoy.
