This is a photo of the Variegated Glacier which lies in the St. Elias Mountain Range of Alaska.  You can see a relatively flat snow covered area at the top of the photo.  This is an ice field where snow collects and gets compacted.  This is also called the accumulation area.  Ice then moves under it's own weight down the valley creating a "river" of ice called a glacier.  When it exits the valley the ice spreads out like pudding and cracks form in the ice called crevasses.  Ice is a material that is both brittle and plastic.  This means that it can flow but that if it experiences a sharp contrast in speed (e.g.. low speeds before an icefall to high speeds after the icefall) it will crack. Click here to get a close up look at what a crevasse looks like.  This photograph from the American Geographic Society Collection archived at the National Snow and Ice Data Center, University of Colorado.
 
 
 


 

The image on the left shows how snow gets compacted to form ice.  It takes a long time (and a lot of snow!) to form a large glacier from compaction.  However, you make "glaciers" every year on the sidewalks in the winter, when people forget to shovel the snow.  Eventually, after many people walk on the snow, it gets compacted and icy...just like a glacier.  What happens to the air that remains in the ice?   There are many people interested in drilling ice cores in Antarctica and Greenland.  They can analyze a number of properties of the ice cores to determine past climate history.  What is climate, and how is it different from weather?  One thing that is being analyzed from the Vostok ice core (Vostok is a Russian station on the East Antarctic Ice Sheet) is the amount of carbon dioxide left in the air trapped in the ice as bubbles.  What does the amount of carbon dioxide in air bubbles mean in terms of the past climate?  For more information, and a look at some of the data retrieved from ice cores click here.
 
 














The image on the right shows a magnified ice core taken from a glacier.  If you cut the ice thin enough, put a light under it and look at it through a polarizing lens you can see the individual ice crystals.  The different colours of each crystal represent different directions that the ice crystals are oriented.  The variety of colours in this sample indicates that there is no preferred orientation for the ice crystals in this sample.  How do you think ice crystals can become preferably oriented?  In general, the ice crystals are smooth and rounded. Why are ice crystals so round?  (hint: look at the image from above).  You can see from this image that ice in glaciers is not entirely composed of frozen water.  There are a lot of impurities within the ice including wind blown debris, till and air bubbles.  How might the amount of impurities change if you looked at a number of sections of an ice core that went from the surface ice to the basal ice?
 

The picture to the left shows a cross section through a glacier and labels all of the relevant parts of a glacier.  Not only do Glaciologists name the different parts of a glacier, but they also name the different types of glaciers....not every chunk of ice is a glacier!  Names are assigned largely based on the shape of the glacier.  Antarctica consists of large ice sheets.  There aren't too many ice sheets around these days...one in Greenland and two in Antarctica.  As the ice sheet builds up, ice begins to flow away from the centre of the sheet.  Sometimes flow is concentrated in ice streams which are faster moving becomes compacted to form glacial ice.  Where the ice streams flow into the ocean they form an ice shelf.  The ice shelf discharges ice bergs.  In mountainous regions you can find alpine glaciers, like the Athabasca Glacier seen along the Icefields Parkway in Alberta.  There are also rock glaciers which are like alpine glaciers, but composed mostly of rock with some ice holding the rock together.