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.

Perched erratic boulderThis large granite boulder is resting above glacially rounded bedrock in the Northwest Territories, Canada. The large boulder was positioned when an ice sheet carrying rocks eventually melted. Then, the debris within the melting glacier settled out, perching the large boulder on top of the smaller rocks. —Credit: Photograph by Lynda Dredge. Copyright Natural Resources Canada, Geological Survey of Canada.

Perched erratic boulder, Newfoundland, CanadaThese blocks and boulders in Newfoundland, Canada, were deposited on this granite surface by melting glaciers. Erratics are frequently left behind in very unusual and precarious positions. —Credit: Copyright Natural Resources Canada, Geological Survey of Canada.

Erratic boulder, Manitoba, CanadaThe size of this erratic boulder in northeastern Manitoba, Canada, can be estimated by noting the person standing in front of the block, on the left side. The plain that the block is resting on is covered with boulders carried by the Keewatian Ice Sheet. —Credit: Copyright Natural Resources Canada, Geological Survey of Canada.

Erratic boulder, Manitoba, CanadaGlaciers once covered this plain in northeastern Manitoba, Canada. They scoured away the landscape leaving only solid granite rock and erratic boulders like this one. —Credit: Photograph by Lynda Dredge. Copyright Natural Resources Canada, Geological Survey of Canada.