Glacier Landforms: Erratics

Glacial erratics are stones and rocks that were transported by a glacier, and then left behind after the glacier melted. Erratics can be carried for hundreds of kilometers, and can range in size from pebbles to large boulders. Scientists sometimes use erratics to help determine ancient glacier movement.

Photograph of erratics in Yosemite National ParkThese glacial erratics were left behind on the fractured bedrock at Olmstead Point in Yosemite National Park. —Credit: Roger H. Goun

Photograph of erratics near the Beartooth Mountains, MontanaGlacial erratics dot the landscape near the Beartooth Mountains in Montana. —Credit: Brian Washburn

Photograph of Okotoks Erratic, CanadaBig Rock, also known as Okotoks Erratic, is located near the Canadian town of Okotoks, south of Calgary, Alberta. Weighing in at 15,000 metric tons (16,500 tons), it is the world’s largest glacial erratic.  —Credit: Jon Noad

Photograph of Tripod Rock erratic, New JerseyIn this photograph from Pyramid Mountain in New Jersey, a huge glacial erratic remains exactly where the glacier left it—perched on top of three other boulders to create a formation known as Tripod Rock. —Credit: Wally Gobetz