The birth of a glacier
What does it take to grow a glacier?
 Growing a glacier requires two essential ingredients: adequate
snow fall and a cool climate. In warm climates, high mountain peaks may
recieve heavy snowfall in the winter, only to have it melt away during
the warm summer months. A cool climate means cool summers. In a cool climate,
some winter snow may survive each year, providing a base for the next
year’s snow. Glaciers can grow only when the amount of snow that accumulates
is greater than the amount that melts each year. Heavy winter snowfall
and cool summer temperatures both favor the growth of glaciers.
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| This image was taken in Summer near Glacier Bay National
Park in Alaska. You can easily see that snow at lower elevations
has mostly melted, while snow near the peaks persists. Only at
high elevations can we find the right conditions for glacier growth.
Click on image to see at full size. |
If conditions are right...
Over many
years, perhaps a few centuries, layer upon layer of snow builds up. As
the mass thickens the weight of the snow presses down, forcing the snow
at the base of the glacier to recrystallize into dense glacial ice. Eventually,
when the ice reaches a thickness of about 100 feet, the ice begins to
squeeze outward and move under the pressure of its own weight. Once the
ice starts to flow, it’s no longer just a thick lump of ice-a glacier
is born!
As the glacier flows downhill,
it descends to warmer zones where the snow melts from year to year. The
boundary where snow melting equals snow accumulation is called the annual
snowline. The snowline varies from year to year depending upon the
amount of snowfall (precipitation) and temperature. |
