The Shrinking Boulder

How big do you think the boulder is in my first picture? Can you see my keys on top of it? I put my keys on top so you could see the size of the boulder. This boulder used to be clinging to the side of a mountain. Something broke it off of the mountain. Sometimes tree roots grow in between rocks. When the root grows bigger, it pushes the boulder off of the mountain. Something else can break boulders off of mountains. It is water, or rather ICE. When water freezes it gets bigger. So, sometimes water seeps in between the boulder and the mountain. Then in the mountains, the water freezes. The water grows or "expands" and pops the boulder off of the moutain. Sometimes earthquakes shake loose boulders off of mountains.

We learned on November 4th about the power of water. Water gushing through a creek bed after a rain will push, or "transport" a boulder downstream. As the boulder tumbles and spills downstream, it gets chipped and broken. The boulder breaks into smaller pieces called rocks. You can see boulders with rocks around them in the second picture.

This process continues. The wind blows and removes pieces of the rock. The rain washes away parts of the rock. The rock shrinks. It becomes a stone. This process of rocks getting worn away is called erosion. Erosion can happen from rain, wind, waves, or glaciers.

Erosion continues and the stones get smaller and become pebbles. See all of the beautiful colored pebbles in the fourth picture? Why are there so many different colored pebbles? Did you say, "Because they are made of different things?" If you did, then you are correct. Rocks are made of all kinds of elements. We'll talk about this later.

These pebbles keep rubbing against each other as they are tossed downstream. It is like they are being rubbed with sandpaper. The pebbles get broken down into smaller bits called sand. Sand appears to be gray or brown. Look closely, though, and you can see all different colors mixed together.
Finally, sand gets crushed into a fine powder. Do you know what is made when you mix the powder with water? It makes clay! Dishes and vases can be made of clay that has been cooked in an oven. Have you ever played with squishy clay? In the winter and spring, the fine powder mixes with water and makes clay. This clay settles to the bottom and the sides of a stream. Then the hot, hot summer comes. What happens to the clay? Correct, all of the water dries out of it. So pieces of dried up clay crack apart and look like broken dishes. (These pictures are from last week, before it rained.)


So we see that a boulder pops off a mountain side and gets pushed down a stream. The boulder erodes by being beaten by weather and chipped by other boulders. It keeps moving down the creek bed, and gets smaller. It turns into a rock , then a stone, then a pebble, and then sand. The sand breaks down into clay and gets placed or "deposited" far away from the mountain where it started.

If you were a boulder, where would you like a stream to deposit you?

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