Glaciers

Glaciers form when snow falls, doesn’t melt, and becomes compressed.  It takes a couple of years before any particular snow fall can be considered a glacier.  When the snow first begins to compact there are lots of air bubbles so the ice looks white.

My family in front of Exit Glacier

Look at an ice cube from your freezer.  It is white because of air bubbles.  If you look closely you can see the air bubbles.

As ice becomes more and more compressed, it turns blue because the air bubbles are pushed out and the only light reflected is the blue.  This is a property of water molecules that they reflect blue light and absorb the other colors.

Glaciers aren’t just blue or white though.  They can be many different colors depending on what they collect.  There are black glaciers, full of vocanic ash, or brown or gray if they’re full of dirt and rocks.

Glaciers melt, but they also flow.  They actually move downhill toward the valley or the sea.  After growing for awhile they become so thick  and heavy that the pressure on the bottom layer of the ice causes a phenomenon known as plastic flow.  The molecules deep down stay frozen but the pressure pushing them downhill is greater than the force holding them together so the layers flow over each other.  As they flow they scrape and grind their immense weight over the ground leaving shattered rock and bits of sand behind.  This ground up material is called alluvial material.  Sometimes the rock gets pulverized so finely that we call it rock flour.  Rock flour can color the streams and lakes of glacial melt water.

  • Make your own glacier.  In a paper cup, freeze layers of water and rock/sand.  Once you have the cup full, place it on a sightly inclined board and watch it travel and disintegrate like a glacier on the move.  It will leave behind interesting trails of sand and rock like a real glacier does.
  • To show that pressure really can melt ice try this.  Freeze a big chunk of ice in a bowl.  Remove the ice from the bowls and place it on a board over the bathtub or a sink.  Place a wire with heavy weights at each end draped over the ice.  Check on your ice chunk every 20-30 min.  The wire will cut straight through the ice, but the ice will refreeze after the wire has gone past.  Great pressure can cause ice to melt, just like the pressure at the bottom of the glacier can cause melting or plastic flow.

The top layer of ice stays frozen rigidly and solidly though and so huge cracks can form along the surface.  these cracks are called crevasses and can extend hundreds of feet down into the ice.

Sometimes glaciers flow into the sea, where they lose big chunks that go floating off.  We call this calving and the chunk floating in the sea is called an iceberg.  Small icebergs are called bitty bergs and growlers.  Only about 10% of the iceberg shows above the water.

To see this, float an ice cube in a glass or bottle of water.  How much ice sticks above the water line?

Iceberg in a Bottle

There are permanent glaciers on high mountains and at the North and South Polar regions.  Antarctica has such huge, heavy glaciers that the land under them is below sea level.

Scientists have named the parts of a glacier.  It can get pretty complicated, but here are some basics.  The area where a glacier originated is called the head.  The bottom end of the glacier is called the terminus.  The upper part of the glacier is called the accumulation zone, because ice builds up quicker than it melts up there.  The bottom area of a glacier is called the ablation zone.  This is where the glacier is melting more quickly.  The accumulation zone and the ablation zone are divided by an imaginary line called the equilibrium line, where accumulation and melt are about equal.

The water melting from a glacier is called glacial melt and sometimes forms glacial lakes.

Earth goes through natural cooling and warming periods.  When earth is cooler like in the ice age, or the little ice age, there are more glaciers and the ice caps grow.  When earth is warmer like in the time of the dinosaurs, the ice caps are much smaller and there are fewer glaciers.  In the early middle ages the world was warmer as well.  Vikings who sailed to Greenland built permanent settlements that were productive and fruitful.  Later as Greenland grew colder, the Vikings abandoned their settlements.  Right now we’re in between the coldest ice age and the warmest periods.

Use a world map and this site to draw your own map of today’s glaciers.

Additional Layers:

  • The sky is blue for the same reason that compressed ice is blue, water in the atmosphere reflects blue light and absorbs other wavelengths.  Learn more about how light allows us to see colors.
  • Alluvial fans, where glaciers have passed through are unstable and in an earthquake they will slide, possibly causing buildings to collapse.  What kind of soil is best for earthquake proof building?
  • Water is unique in that in solid form it is less dense than in liquid form.  It floats on itself.
  • Scientists call the frozen water on earth, especially the ice caps, the cryosphere.  “Cryo” means cold.  What other “spheres” do scientists talk about?
  • Mars has polar ice caps made of frozen water, very much like earth’s.
  • Learn more about the little ice age, a period in the 1300’s -1850’s when the earth was colder.
Tagged , , . Bookmark the permalink.

Leave a Reply

Your email address will not be published. Required fields are marked *