Kettle

I live near a park called the Warsaw Caves. The caves in the park are not your typical caves. They are glacial limestone caves - meaning they were made by retreating ice and glacial rivers during the latter stages of the last Ice Age, and meaning they are dark, tiny, crawl-about-on-your-hands-and-knees caves.

But the caves were not the only things the retreating ice left behind. They also left behind drumlins, eskers, and another anomalous formation called a 'kettle'. A kettle is a roundish, almost smooth hole that can be found in the limestone rock in this area. They can be small (perhaps a hands width across and deep) or quite large (like the one in my photo here, which two large adults could fit inside). The theory of how they formed is this: As the ice retreated and melted, glacial rivers began flowing southwards, carrying hard pieces of granite from the north (the Canadian Shield) over this area just outside of Warsaw, which is mainly limestone (a much softer rock). The pieces of granite were caught in eddies and began swirling and scraping over the limestone, eventually carving out these kettles.