Are you one of those sort-the-spice-drawer-alphabetically people? Someone vexed by a sock just sitting there on the bedroom floor, or by a driver who can’t abide by the painted lines in a parking lot? Well, you probably hate glaciers.
As these rock-churning monsters grind back and forth across the planet, they pick stuff up when it suits them and discard it when they leave (melt, that is), including what are known as erratics. These large boulders and rocks may be moved hundreds of miles from their original location over the course of thousands of years. Once dumped, because they have a different composition than the material around them, erratics provide valuable information to scientists about the age and scale of the glaciers that shoved them around. They can also be spectacularly out of place.
Unlike other glacial castoffs, such as moraines and drumlins, erratics stand alone. They can be enormous: Alberta’s Okotoks checks in at more than 18,000 tons, the largest known erratic in the world. Many less prodigious relocated rocks are even more photogenic, such as Northern England’s Norber Erratics, some of which perch on impossibly slender limestone supports.
Some locations are just sick with erratics. In Southern Wisconsin, for example, Devil’s Lake is home to a whole collection of wayward rocks. They were dumped there around 20,000 years ago, when an advancing glacier smashed into the nearby Baraboo Hills, which are more than 1.6 billion years old. The Baraboo Hills have been around that long because they’re made of extremely hard quartzite. The glacier realized it had met its match and retreated to the northeast, leaving behind countless boulders, some of which weigh 85 tons or more.
You can find erratics and other glacial debris on every continent, often in places you might not associate with monstrous walls of ice pushing rocks around like they own the place. In the journal Science Advances in 2021, researchers described numerous erratics in the Bale Mountains of Ethiopia, deposited there more than 28,000 years ago. And, while Namibia’s Twyfelfontein region is best known for rock art spanning the last 6,000 years, glaciers left their mark much earlier. About 300 million years ago, fast-moving ice sheets created dozens of drumlins, or ridges of mud, rock, and other glacial junk. About 100 of the drumlins still dot the desert landscape today.
We’re all for a well-organized natural world, but we just love the audacity of erratics. Here is a pile of our favorites.