Book 5, Question 52 · Video
Scratch Marks! Why Do Glaciers Scratch the Rock?
Glaciers carry rocks and gravel frozen into the bottom of the ice. When the glacier moves, those stones scrape across bedrock like sandpaper and leave long scratches called striati
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What Crafty Clover says in this video
Intro
Hi! I'm Crafty Clover! Let's discover something amazing. Why do glaciers leave scratches on rock?
The Big Idea
Sometimes, when a glacier melts away, it leaves a bare rock covered with long, straight scratches. Those scratches were made by stones in the ice, which act like nature's sandpaper. They are clues to where the glacier used to be. Let's see how!
Step 1
Step one: stones get stuck in the ice. As a glacier slides along, it pulls loose rocks from the ground and freezes them into its bottom. Now it has a belly full of grit.
Step 2
Step two: the heavy ice drags the stones along. The stones are pressed hard against the bedrock below, and they scrape and scratch it as the ice slides by. It works just like sandpaper on wood.
Step 3
Step three: scratches are left behind. When the ice melts, the bare rock shows long, straight grooves. Scientists call them striations. The scratches point the way the ice was flowing.
A Closer Look
Let's look closely at a scratched rock. These long, straight lines are the scratches. They all run the same way, along the ice's path. And smooth, polished patches show where the ice rubbed hardest.
Quick Facts
Quick facts! Scratches on bedrock show which direction the old ice went. Ice can also carry giant boulders far away and drop them. These are called erratics. The powdery dust the ice grinds is called rock flour, and it can turn meltwater a milky blue. The scratches you see today may be more than ten thousand years old!
Think Like a Scientist
Now, think like a scientist! Make your own scratches with a grown-up. Drag a small pebble across a bar of soap, in one direction. Look at the lines it leaves. Which way do they point? What clues do scratches on a rock give you?
Outro
Every scratch on a rock is a message from the ice. Now you know how to read it! Crafty Clover can be found on Amazon Books, Google Bookstore, and Apple Books. Available for purchase or download! Bye for now!