Photographs by Thomas McGuire
Written by Martin Richard
We have been talking about glaciers. One way to think about glacier is, they are rivers of ice.
But sometimes glaciers can be much larger than rivers. They can be oceans of ice, like the glaciers that cover Antarctica and Greenland.
What would an ocean of ice do to the land beneath it? What would the land look like when the glaciers melt away?
Let’s start by thinking about rocks in fast-moving streams.
Stones in mountain streams are often round and smooth. How does that happen?
As the water moves them, they bump into other stones. Their corners and edges get knocked off, and they get round as they roll down the stream. As sand rubs against them –and they rub against sand– the smallest edges and corners get knocked off too, and they become polished and smooth. That takes a lot of rolling, so it takes a lot of time.
Now look at these pictures of mountains. The mountains on the bottom are all jagged and sharp. The mountains on the top are more round, more smooth.
So which of these mountains are older?
The ones that are round and smooth are older! Their edges have been worn off.
What could wear a mountain down? And how long does it take?
Water wears the mountain down. Water erodes it away. All those rocks moving down streams and rivers do not move back up the mountain.
Sometimes the water is ice! A glacier! Glaciers are like bulldozers –actually, several lines of very slow bulldozers– and push huge amounts of rock downhill.
Back to our first two questions: What would an ocean of ice do to the land beneath it? It would wear off the edges and corners of the land, making it rounder.
What would the land look like when the glaciers melt away? It would look like the mountains in the top picture!
Those worn-down mountains are in the Hudson Highlands in New York. There is good evidence that they were once covered completely by glaciers, sometimes a mile deep! These mountains were worn down by ice, lots and lots of ice, covering the whole landscape, pushing it down and wearing it away.
The mountains on the bottom are from the Rocky Mountains, in Colorado. They are still growing! They are very young compared to the old, rounded mountains in New York.
How long does it take to wear down a mountain?
Well, the evidence shows that the rounded mountains in New York stopped growing 250 million years ago. (That’s about 20 million years before the first dinosaurs.) So a good answer is, it takes a couple of hundred million years to wear a mountain down, to make a mountain smooth and round instead of jagged and sharp.
The original EPOD can be found here.
Photograph by Marli Bryant Miller
Written by Martin Richard
This huge rock is in the Willamette Valley in Oregon. It is different from all the other rocks around it.
How did it get there? Where did it come from?
Here is one clue: it has parallel scratch marks on it! Those scratch marks are found on rocks that have been dragged by glaciers. (We wrote about that right here.)
So we are very sure that this rock was scratched when it was dragged by a glacier.
What else do we know about this rock?
Scientists have taken pieces of this rock and analyzed the minerals. The minerals are the same as rocks from northwest Montana. That’s over 500 miles away!
So we have good evidence that this rock came from northwest Montana and that a glacier dragged it around.
Were there glaciers in northwest Montana?
Yes, at the end of the last ice age, northwestern Montana was partially covered by glaciers. But this rock is in the Willamette Valley of Oregon! The glacier was not 500 miles long.
But there is a way that a piece of a glacier could have gotten to Oregon. It could have floated there, as an iceberg!
Floated on what?
There is no ocean between Montana and Oregon. There is a river though. Well, not one river, but a system of rivers, which flow from Montana all the way to the ocean. Those rivers flow into the Columbia River, and this rock is near the Willamette River which flows into the Columbia.
Could an iceberg from a Montana glacier have made it all the way to Oregon?
Yes!
There is a lot off evidence that there was a huge lake in northwestern Montana at the end of the last ice age. A huge glacier from Canada made an ice dam on the Clark Fork River. The lake that formed behind the dam is called Glacial Lake Missoula. It was more than a thousand feet deep at the dam, and it was huge. Glacial Lake Missoula covered almost 3,000 square miles, and held more water than Lake Erie and Lake Ontario combined!
(Actually, the glacier dammed the river several times. But the first lake that formed seems to have been the deepest and the biggest, and we are going to talk about that one.)
When that first ice dam broke, all that water behind it burst out in a huge wall. In some places, the wall of water was more than 500 feet high!! There is evidence that the water moved through the narrow valleys at almost 60 miles an hour!
We can tell how deep the water was, because it stripped off the soil of the valley walls, stripped it right down to the rock. Multiply the height of the valley by the width and multiply that by the speed of the flow and you get the volume of flow per hour: 9 cubic MILES of water per hour.
Let’s try to imagine 9 cubic miles of water. The next time you go outside, look to the east, where the sun comes up. Look at something you think is two miles away, and imagine a line going there. Now look to your right, to the south. Look at something in that direction that is two miles away. Imagine that line. Those two lines make a square two miles on a side. It has an area of 2 x 2 = 4 square miles.
Now look straight up and try to imagine a line two miles high. You are now standing at the corner of an imaginary cube, 2 miles on each side. Your cube has a volume of 2 x 2 x 2 = 8 cubic miles.
Now fill that cube with water.
Make the sides just a bit longer, to just under two and a tenth miles (2.08, actually), and you have 9 cubic miles of water.
That’s how much water flowed at the peak of the flood from Glacial Lake Missoula. In an hour!
How does that compare to other rivers?
The Amazon has the largest flow of any river in the world: about one hundredth of a cubic mile per hour. So the flow of the Glacial Lake Missoula Flood was 900 times bigger!
Try to imagine 900 Amazons in one flood!
A cube of water one yard on each side weighs just about 1,700 pounds, just under a ton. Imagine the weight of YOUR cube of water, two MILES on each side. Imagine the force and the power of that water as it raged through the canyons at 60 miles an hour, with giant whirlpools breaking and stripping the rock itself. Imagine the roar of the water, the crashing of great boulders slamming into each other and into the valley walls.
That would make a great movie!
But let’s get back to our rock.
The rock has parallel scratch marks. That tells us it was once in a glacier. The minerals of the rock tell us it came from northwest Montana. Other evidence tells us there was once a huge lake in behind an ice dam in northern Montana. That lake had glaciers on its shores, which means there were icebergs on the lake.
When the ice dam broke, it unleashed a gigantic, humongous, terrifying, titanic, stupendous, colossal, awesome monster of a flood, which ripped apart and re-arranged the land as it raged to the sea, carrying icebergs which carried rocks and carried this rock 500 miles.
What a trip this rock has taken, what a tale this rock could tell!
Oh wait. It IS telling us.
All we have to do is pay attention, collect the facts, and imagine the story that explains the facts. When we do that, this rock tells us a great story: of the humungous floods from Glacial Lake Missoula.
You want to learn more about the story of Glacial Lake Missoula and the Humungous Flood? You could start here, and explore the links.
Last week we looked at a U-shaped valley carved by a glacier. Maybe you wondered, where did all the rocks and dirt go?
In this week’s picture, we see where some the rocks and dirt carried away by the glacier ended up.
As the glacier moves down a mountain, it moves into warmer air and starts to melt. It melts from the sides where the ice is thinnest.
Most of the rocks and dirt are left behind in long piles that run along the sides of the glacier. The piles of dirt and rock are called “moraines,” which is pronounced “more RAINS.” Those moraines along the sides of the glacier are called “lateral moraines.” That is pronounced “LAT er ul,” which means “on the side” or “to the side.” If you know American football, you may have heard of a “lateral pass,” where the quarterback passes to the side instead of downfield.
This picture is of a lateral moraine from a glacier in Canada. You can see the glacier at the bottom of the picture. If all of the glacier melts away, the moraine will still be there. There are a lot of places on our planet Earth where you can see the path of a glacier that was once there, when you see the moraines the glacier left behind.
You can read more about this picture here: Athabasca Glacier Lateral Moraine
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.
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.
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!
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.
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.