Carleton’s Kettle Hole Marsh sits alongside a trail through the prairie in the Lower Arboretum. The marsh, now covered in ice and cattails, is about 10,000 years in the making. Its story begins at the time of Minnesota’s last glaciation.  

About 15,000 years ago, an ice sheet covered most of western Minnesota. Over the course of 6,000 years, the glaciers retreated northwards, leaving chunks of ice scattered throughout the landscape. Some also floated downstream on major waterways, washing ashore during periods of intense flooding. These chunks then melted, leaving an array of “kettle lakes” behind. Most of Minnesota’s 11,842 lakes—from the 5.1-square-mile Red Lake to tiny Kettle Hole Marsh—were formed through this process. 

Over the past centuries, water and sediment from nearby farmland have collected in Carleton’s Kettle Hole, turning what was once a lake into a marshy wetland. The rate of sediment deposition has varied over time, accelerating in the mid-1900s from intense cultivation, but since decreasing due to conservation practices. Only a small section of standing water remains.

As the only body of water in the Arboretum that does not drain into the Cannon, Kettle Hole is a springtime refuge for frogs and toads. When the ice melts later this month, western chorus frogs, wood frogs and northern leopard frogs will emerge by the thousands, their calls a deafening chorus. As they mate throughout the spring, they will be protected from predators by a glacial depression formed more than 10,000 years ago.