KEPOW

Glacier Lesson 4

Photograph by Martin Richard

Written by Martin Richard

Last week, we looked at scratch marks in rocks. They showed us that a glacier was once there, and scratched the rocks by dragging other rocks across them.

In this picture we see something much larger made by a glacier: an entire valley!

All of this valley was carved by a glacier!

Most of what you see here was once covered in ice. Only the tops of the highest mountains were above the ice.

Rivers carve valleys too. How do we know this was carved by a glacier? There are two clues.

First, this valley is shaped like a U! Rivers carve valleys that are V-shaped. Glaciers carve valleys that are U-shaped.

Second, you can see a long way down this valley. Rivers wander. They have lots of curves and you usually cannot see a long way down their valleys.

Why is this?

The water at the bottom of a river moves more slowly than the water at the top. Rivers erode the land where they move the fastest, which is at the top of the river. So they erode away their edges and get wider. That is how they carve a V.

Rivers go around things in their way, but they have to go downhill, so they wander. As they become curvy, the river moves faster at the outsides of the curves. So the river eats away the land at the outside of the curve, and makes larger curves, shaped like an S.

When glaciers form, they start in the high mountains, where it is coldest. As they grow they move down into the valleys already carved by rivers. BUT! Glaciers are not rivers! Rivers, remember, erode the land where the move the fastest, at their tops. Glaciers erode the land where they are deepest!

As a glacier moves down a valley that was carved by the river, it erodes the bottom of the valley, the bottom of the V, and makes the sides steeper and the bottom flatter. That is why glacier valleys are shaped like a U.

Glaciers pile up and run right over hills that are in its way. The glacier then erodes the hill away. So glaciers straighten out the S-curves left by the river, and you can see a long way down the valley.

A big glacier can plow a straight valley with a view that is many miles long.

I took the picture above in Glacier National Park. I was standing on a very steep cliff at the head of this valley. (If I had taken five steps forward, I would have fallen hundreds of feet straight down.) You can see the U-shape of the valley, and the cliff I was standing on was even steeper than the sides you can see in the picture.

The glacier that carved this valley was not the biggest glacier in the park! It fed ice into a much larger glacier that carved a valley more than 20 miles long!

So the next time you are in the mountains, and you notice that you can see a long way down a valley, look to see if the valley has steep sides and is shaped like a U. if it does, you will know that the valley was carved by a glacier!

You can read more about this picture here: Going to the Sun Road and the Garden Wall That page was not written for kids, but you might like reading it anyway.

Glacier Lesson 3

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.

Glacier Lesson 2

Photograph by David Lynch

Written by Martin Richard

Last week we looked at the longest glacier in the Alps. We saw it from the outside, looking down from a nearby mountain.

In this week’s photo, we are looking into a glacier. It’s white on the top, but turns blue deeper inside. The white is from the snow. That’s not a surprise, since glaciers are made from snow. Where does the blue color come from?

A swimming pool is blue at the deep end. A glacier is bluer the deeper it gets.

Maybe they both turn blue for the same reason?

Yes, because they both have something to do with how light behaves when it goes through water.

What we want to know is, why does white light turn blue when it goes through a lot of water? Whether water is liquid (sloshing in a pool), or ice (frozen in a glacier), the light turns blue.

To understand the color of glaciers and swimming pools, you have to understand rainbows!

White light is actually light of all colors mixed together. You can separate white light into its colors by shining it through a prism. Here is a picture of a prism casting the spectrum of white light.

When you shine light on a prism, the light has to cross the edge of the glass. Crossing the edge pulls the light apart into its colors. To go through a prism, the light has to go through two edges so the colors get separated even more, and now you can see them.

When you shine light through a prism you get a rainbow of light. All the colors of a beam of light are called its “spectrum.” A rainbow shows the spectrum of while light.

Raindrops act like prisms...millions of them. Millions of raindrops have millions of edges and cast millions of spectrums. (Ooops! That’s not quite right. We don’t say “spectrums.” Spectrum is an old word and we still use the old plural, which is “spectra.” So let’s correct that sentence to say …)

Millions of raindrops have millions of edges and cast millions of spectrums spectra. We see all those spectra in the shape of a bow.

Dump those raindrops in a swimming pool – or in a glacier! – and the drops are not separate any more. All the edges are gone! No edges means no prisms means no rainbows!

The light in the pool or the glacier has to go through a lot of water. Water absorbs the red and orange colors. So you can’t see the reds and oranges; they are trapped in the water! The more water you have, like in the deep end of the pool, the more red and orange gets taken out.

But water does NOT trap blue light! Blue goes through!

So the glacier does not TURN the light blue; the blue was always there. The deep, frozen water of the glacier TAKES AWAY most of the colors EXCEPT blue.

What is really important in this week’s photo is what you DON’T see: you don’t see the red and orange light that was trapped by the water of the glacier. What you DO see is the blue light that escaped and made it all the way to your eyes.

We got this picture of the glacier here: Blue Glacier Ice. It is not written for kids, but you're welcome to check it out!

Glacier Lesson 1

Photographer: Piero Armando

Summary Author: Martin Richard

Look at this river of ice!

It’s a glacier, which is almost 14 miles long. It’s the longest glacier in the Alps, the Altesch Glacier, in Switzerland. It’s a mountain glacier.

Another word for mountain glaciers is Alpine glaciers, because Alpine is an old word for mountain.

Mountain glaciers start in the high mountains and move down, into the valleys. How do glacers form?

Glaciers grow where the snow piles up and does not melt. Glaciers melt at their low end. If more snow piles up on the high end than melts on the low end, the glacier grows. If more melts than piles up, the glacier shrinks.

Mountain glaciers flow downhill, but they do not flow quite like water.

The top part of the glacier is brittle It cracks like ice. But underneath the top of the glacier, the weight of all the ice pushing down changes the way the ice flows. The bottom of the glacier flows like syrup. Very, very, very cold syrup.

The brittle top is carried along by the slowly-flowing bottom. Because it is brittle,the top can break. The cracks in the ice are called crevasses. They can be very deep. Snow can cover and hide them, which is very dangerous to hikers and climbers.

The glacier tears the mountain down! In two ways.

The first way is, the glacier plucks rocks right off the mountain! At the head of the glacier, water seeps between the glacier and the mountain. It seeps into the cracks of the rocks. When it freezes, it cracks the rocks, and the glacier grabs the pieces of rock and carries them away.

The second way is, the glacier scrapes the rocks away. The rocks carried by the glacier scrapes the rocks on the sides of the valley. That wears both rocks down.

The glacier carries all that rock and dirt and it piles up along the sides of the glaciers. A huge pile of dirt and rock piled up and left by the glacier is called a moraine. Two glaciers can come down two valleys and join. They merge, and so do their moraines, carried by the glacier. Look at this picture. See the darker stripes in the glacier? That’s a line where two glaciers joined together!

If you want to learn more about this picture, you can read about it here: Aletsch Glacier in Switzerland It is not written for kids, but you can try it.

We will look at more pictures of glaciers and write about them for kids, right here. Then we will choose another subject, and write about it for you, every week.

Earth Science for Kids

This site is about the science of the earth.

Every week we take an earth science picture and write about it for kids.

We get our pictures from Earth Science Picture of the Day, which we call EPOD.

EPOD puts up a picture every day. We put up a picture every week, so our site is called Kids’ Earth Science Picture of the Week, which we call …

KEPOW!

We are just getting started but EPOD has been around for many years, so we have lots of pictures to choose from. That means we get to choose pictures that are all about the same thing. We decided to write about glaciers first.

We hope you like our site and learn something about the earth when you read it. Look for our first post on Monday, December 10, 2012.