Photograph by Nel Graham
Written by Martin Richard
Glaciers sometimes melt away. Several thousand years ago, the earth was cooler and many mountains had glaciers. The mountains are still there but the glaciers are gone. How can we tell that a mountain once had a glacier?
When we look at glaciers that are still here, we can see that they carry a lot of rocks. There are rocks trapped in the ice on the very bottom of the glacier. The glacier carries those rocks along and they scrape against other rocks.
So one way we can tell that a glacier was once on a mountain is to look for scratches and scrapes on the rocks.
Look at the rocks in the picture above. They are on the top of a mountain in California.
In the picture you can see stripes running across the tops of these rocks. Those are scratches in the rocks. They were made when a glacier dragged other rocks across the tops of these rocks. scratching them.
All of the stripes run the same way! They are parallel to each other. This shows us the direction the glacier moved when it was here.
Marks like these tell us that, once upon a time, there was a glacier here!
Here is where we got the picture of these scratched rocks: Devil’s Postpile Tile Pattern That page is written for grown-ups, but you can check it out if you wish.