Do you see the lines on the rock? These lines were created by glaciers! For two million years, glaciers have been present in North America. They have advanced and retreated over the land several times. When the earth began to warm, the glaciers finally retreated to their current positions. The most recent time in which the glaciers began to retreat was about 15,000 years ago. We can still see evidence of the effects that glaciers had on our landscape today. Glacial striae is caused by the physical grinding of ice against rock. It usually looks like a lot of straight parallel lines. They are created by the boulders and sediments which are carried under the glacier. Glacial striae can tell us a lot about what was done to the landscape as the glaciers grinded down layers of rock.

rock exhibiting striae- parallel groove marks on its surface

Glacial striae, Peter Russell Rock Garden