Virtual Exploration #3
How do Glaciers Shape the Land?

This image was taken by Matthew Durant 
at Wrangell St. Elias National Park.

Home    What is a Glacier?    How do Glaciers Form? 
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How do Glaciers Shape the Land?

 

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I want to embark on Virtual Exploration #3

 

   Virtual 
 Exploration

Virtual Exploration #3
How do Glaciers Shape the Land? 

Glaciers change the land by eroding it in some places and depositing the rocks that are plucked up elsewhere.  We'll explore these things: how glaciers carve out awesome u-shaped valleys; spit out massive amounts of rock that pile up into glacial moraine; we'll climb on massive boulders (glacier erratics) that were dropped on the tundra plane; we'll soak our sore feet in kettle lakes that were made by glacial erosion; we'll marvel at rock striations; and we'll watch cloudy rivers rage on and on.  Let's go!!!

	U-shaped Valleys We are only a few miles into Denali National Park, at Riley Creek. Already, we see a wide, u-shaped valley!  About 70,000 years ago, a glacier passed through this river valley (v-shaped) and scraped away (eroded) rock creating a u-shaped valley with a broad floor and steep sides. Later, this glacier receded, leaving only a broad, u-shaped valley.
	Glacial Moraine Look at all of those small rocks all around and on that glacier.  As the glacier moved forward and then receded, it scraped up rocks from the bedrock.  These rocks got stuck in the ice and are moved along with the glacier.   Our fellow scientists call these rocks till.   As the glacier moves and recedes it creates three basic types of moraine.   Check the computer to learn more about three types of moraine.
	Glacial Erratics You pass huge boulder after boulder on your hike to the glacier.  They seem oddly out of place, like they were dropped down from somewhere far away.  In a way, they were. The glacier in front of us once spread far out onto the tundra.  It bulldozed huge rocks in front of it as it pushed forward.  As it began receding back into the mountains, it dropped the huge rocks.  Today, we see huge boulders far out on the flat tundra.  These are called glacial erratics.
	Kettle Lakes Wow, check that out, it's beautiful!  You see the clear reflection of Mt. Denali on the mirror-like surface of Wonder Lake and you think how beautiful the reflection is.  Your friend interrupts your thoughts by saying, "The reflection is beautiful but that kettle lake is amazing!!!"   You already know that as a glacier moves ahead it scrapes up pieces of the bedrock. This scraping forms depressions in the ground.   Many years later, as the ancient glacier receded, it dropped a huge chunk of ice that melted and flowed into that depression.  This formed Wonder Lake (a Kettle Lake).
	Glacial Striation When you look closely at the till in the moraine, you see lots of signs of glacial erosion.  On the bottom of this rock there are long scrape marks.  Wow, that must have been a lot of pressure to scrape those rocks like that.   As the glacier moves, the till trapped in the ice gets scraped along the bedrock.  Pieces of the bedrock get worn off and the till gets scrape marks in it.
	Glacial Flour Look closely at the Toklat River over there.  It is flowing from the glacier.  See it's milky gray color.  That gray color is rock scrapings and small pebbles that were rubbed off of the bedrock as the glacier passed over. The glacier's melt water comes roaring out.  The current is so strong and the water is only about 35 degrees Fahrenheit.   All of these rock particles in the water are known as glacial flour.    The rocks, pebbles, and glacial flour that get caught up in the Toklat River eventually slow and drop to the riverbed.  The great amount of dropped sediment create a gravel bar that diverts the river into another braid.  Soon, more sediment is dropped that creates another, and another, and yet another braid.  Then, a wide glacier river flows swiftly through many ever-changing braids as it flows to the north.

   Online 
 Resources

Glacial Moraine	Good information and diagrams about glacial moraine.
Shaping the Land	Great diagrams of the different ways that glaciers form the land.
Glaciers Shape the Land	An excellent web site that gives good information, links, and images to provide lots of details on how glaciers shape the land.
Alpine Glaciers Shape the Land	A great site to learn more about how glaciers affect the land with maps of real glaciers and their affects.
Illustrated Glossary of How Glaciers Shape the Land	Awesome images backed up by good information on how glaciers shape the land.

   Further 
 Reading

Alaska's Glaciers. Alaska Geographic volume 9, number 1, 1982.

An observer's guide to the glaciers of Prince William Sound, Alaska. Valdez, AK:  Prince William Sound Books,  1987. 

Glacier. R. H. Bailey and the Editors of Time-Life Books Alexandria, VA: Time-Life Books, 1982.

Glaciers  John Gordon.  Stillwater, MN Voyageur Press, 2001.

Glaciers, Natures Frozen Rivers. H. H. Nixon and J. L. Nixon. New York: Dodd, Mead, 1980.

Glaciers of North America: A Field Guide. S. A. Ferguson. Golden, CO: Fulcrum Press, 1992.

Blue Ice in Motion: The Story of Alaska's Glaciers  S. Wiley. Alaska Natural History Assn. 1995.

   Hands-On
 Activity

1. Discussion: What do you know about how glaciers shape the land?
   
   

2. Make a new small model glacier in a plastic cup.  

   1. Add about 1/2 an inch of rocks and sand at the bottom of the cup. 

   2. Cover the soil and rocks with snow from outside or shaved ice that you create by placing broken ice cubes (carefully hammer ice cubes in  a towel) into a food processor. 

   3. To simulate the massive amount of pressure that snow above has on the snow below, place a a small rock on top of the packed snow.

   4. To simulate the cold Alaskan winter, place the shoebox with packed snow into a freezer overnight.  

   5. The next day, add more snow to your glacier and pack down with more weight.  Place it back into the freezer and freeze overnight.

   6. Repeat step E for several days.

   7. Take your model glacier out of the freezer and remove the rock.  Slightly warm the sides of your plastic cup by running it under warm water.  Do this just long enough to get the model glacier out of the plastic cup when the sides are tapped.
      
      

3. To simulate your glacier flowing over bedrock, rub your glacier slowly over a brick, pressing down fairly hard.  What happens to the piece of wood?  Focus your observations on the shavings that are scraped up.  Take notes, make a sketch, and label what you observe in your science journal.
   
   

4. How does your model glacier simulate what happens in the wild with Alaskan glaciers?
   

 Assessment Guide

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How do Glaciers Shape the Land?

 

Home    What is a Glacier?    How do Glaciers Form? 
How do Glaciers Move?    How do Glaciers Shape the Land?

 

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