Boyer Nature Preserve is wonderful, mini-wetland that sits in the middle of suburban Westerville, Ohio. The site’s main feature is its stream-fed pond. Although it may look like an ordinary pond, it’s actually very special due to the way that it was formed. During the last ice age, Westerville was beneath approximately one thousand feet of ice (305 m). As the climate warmed, a large fracture formed near the edge of the melting glacier. Once that fracture became large enough, a huge slab of ice separated from the main body of the glacier and landed with a great thud in what is now known as Boyer Nature Preserve. When huge chunks of ice break off a glacier like this, it’s called calving.
It turns out that the immense glacier over Ohio had eroded great quantities of land as it moved south from Canada, and this eroded material became frozen inside the glacier while it was still growing in size. However as the glacier melted and shrank, it released the sand and gravel that it had carried with it. Together this sand and gravel is called glacial sediment. So much glacial sediment was deposited in what’s now Westerville that it buried the calved-off chunk of ice under a thick layer of sediment, and this sediment kind of insulated the calved ice. When that calved chunk of ice eventually melted, the layer of glacial sediments that used to be on top of the ice sank lower and lower as the ice melted. This created a low area that filled with water from the melting ice. A body of water that’s formed in this way is called a glacial kettle.