How Winona Lake was formed

There is a state historical marker on the northeast lawn of the Kosciusko County Courthouse in Warsaw that explains most of this article in two sentences. The Indiana Historical Bureau's "Indiana's Glacier Lakes" marker, installed in 1966, reads: "About 14,000 years ago melting blocks of ice from the last, or Wisconsin Glacier, formed the kettle hole lakes of northern Indiana. The largest lake, Wawasee, and the deepest lake, Tippecanoe, are in Kosciusko County." Winona Lake is a mile and a half east of that courthouse, and it belongs to the same story.

The ice that rebuilt northern Indiana

Indiana was covered by ice four separate times, and the last of those advances is the one that shaped the ground around this lake. The Indiana DNR's account of glaciers in Indiana describes an ice age lasting more than a million years and ending in Indiana roughly 15,000 years ago, with the Wisconsin glacier reaching a thickness of about one mile as it advanced from Canada across the northern part of the state. The DNR summarizes the result in a sentence: glaciers "flattened hills, buried rivers, dug out new lakes and pushed piles of rocks into new hills called moraines."

That is why the two halves of Indiana look so different. Northeastern Indiana carries the obvious evidence, in lakes, low hills, and boulders that range from the size of a baseball to the size of a small car. Southern Indiana, beyond the ice limit, does not.

How a kettle lake forms

The Indiana Department of Environmental Management's Clean Lakes Program published a plain-language explanation of the mechanism in its Water Column newsletter. In "Glacially Formed Kettle Lakes in Northern Indiana" (Fall 2018), Mitchell Latta describes retreating glaciers calving off large blocks of ice. Those blocks cut into the ground and carved out depressions, the glacier kept receding, and the stranded blocks melted in place as temperatures rose. Depressions that filled with surface or underground water became kettle lakes.

The same article explains why these lakes vary so much. Size and shape depend on the size and weight of the ice block, the rock or soil it settled into, and how much rock and soil was frozen into the block itself. Depth varies less than surface area does. Related landforms come out of the same process: a depression filled by groundwater alone is a kettle pond, one that fills with vegetation and precipitation is a kettle wetland, and one whose water turns acidic as plant matter decomposes becomes a kettle bog.

Latta's article dates the ice to about 16,000 years ago. The historical marker says about 14,000, and the DNR's state parks material says the ice age ended in Indiana about 15,000 years ago. All three are round numbers for the same event, at the resolution the sources intend.

The high ground to the south

The ice left more than holes. The Indiana DNR Division of Water's county water resources assessment, published as "Water Resources and Use in Kosciusko County", describes a well developed moraine around the town of Packerton, about seven miles south of the lake. The Packerton Moraine reaches an elevation of over 960 feet above mean sea level. The Winona Lake surface sits at roughly 811 feet, so that ridge of glacial debris stands about 150 feet above the water.

The same assessment places the Tippecanoe River where the moraine meets a broad outwash plain, a valley of sorted sand and gravel laid down by meltwater, which widens to more than five miles across in the north-central part of the county. It also notes channels and tunnel valleys trending northwest off the flank of the Packerton Moraine, now occupied by present-day streams. Every ditch that feeds this lake runs across that inherited surface, which is part of why the watershed drains the way it does.

What the lake bottom records

The DNR's lake survey sheets list the bottom types found in Winona Lake: boulder, gravel, sand, muck, clay, and marl. The Lilly Center's profile gives a shorter version of the same list, sand, gravel, muck, and marl. The first four are ordinary glacial materials, sorted or unsorted, sitting where the ice and its meltwater left them.

Marl is a lime-rich sediment, and lakes that accumulate it are so characteristic of recently glaciated country that Indiana's state geologists devoted an entire volume to them. "The Lakes of Northern Indiana and Their Associated Marl Deposits", by W. S. Blatchley and G. H. Ashley, ran to nearly 300 pages in the Twenty-Fifth Annual Report of the Indiana Department of Geology and Natural Resources in 1900, five years after the Winona Assembly renamed this lake. The marl on the bottom of Winona Lake is a slow record of hard water shedding calcium carbonate over thousands of years.

A deep basin for a small lake

Winona Lake is deep in a way that only makes sense with the glacial history in front of you. The lake covers a few hundred acres and holds a hole roughly 79 feet deep, with an average depth around 30 feet. Very little of Indiana's surface has that kind of relief left in it.

That retention time follows from the shape the ice left. A basin that deep, fed by ditches that small, holds roughly a year of water before replacing it. That is the reason the summer stratification is so pronounced here, and part of the reason nutrients arriving from upstream stay in the system long enough to matter.

What the sources do not settle

Three things stayed open after this research.

• The specific basin mechanism. The county's lakes are glacial and the region's characteristic lake is a kettle, but no source located for this article states that Winona Lake specifically is a kettle rather than, for example, a segment of a tunnel channel off the flank of the Packerton Moraine. The elongated shape and the single deep hole would be consistent with either.
• The age of this basin. The 14,000-year figure on the courthouse marker applies to northern Indiana's kettle lakes as a group. No date has been published for this lake.
• The depth of the sediment. The DNR sheets record what the bottom is made of, and not how much of it has accumulated since the ice left. A sediment core would answer that and would also date the basin.

The Lilly Center for Lakes & Streams is the organization most likely to have or to develop that kind of local answer, and its research pages are the place to watch.

Where to see the evidence from shore

The glacial story is visible around the lake without any equipment. Rounded glacial stone, the cobble that ice and meltwater sorted and dropped here, is the material Indiana's shoreline rules single out by name for natural shoreline work, because it is native to this lakebed. Boulders too large to move sit in yards and along road edges throughout the county, carried here by ice from bedrock hundreds of miles north.

The shape of the hole itself is easiest to see on the depth map, where the contour lines crowd together along one flank of the basin and spread out across the shallow arm. That map is a picture of what the ice left, drawn in ten-foot steps, and the guide to reading it covers what each band means on the water.