Into Alaska - Alaska and Points North: Tips and Tales from the Road - page 89

INTERESTING INFO:
about Glaciers
Fresh snow is composed of crystals that have sharp protruding points. Since each crystal
is unique, these points hold the crystals apart from each other, creating air pockets in the
loosely-packed snow. But when the summer sun warms the crystals, the sharper points melt
offandthesnowcrystalssettleinaroundeachothermoresnugly,squeezingouttheairpock-
ets and compacting ever more closely into the interlocking crystals, that we know as glacial
ice.
Mostglaciers arebelieved tobethousandsofyearsold.Astheprocessofsnowfalling, melt-
ing and compacting continues each season, the crushing weight from above causes the ice
below to become more taffy-like in nature and it slowly begins to flow downhill.
Understanding the concept that ice can "flow", requires a little explanation. What it involves
is accepting that every substance has an “elastic limit” and when material is stressed by an
amount that exceeds its elastic limit, this “plastic deformation” that permits movement oc-
curs. The example of toffee is used because like ice, toffee will fracture if stress is applied
sharply. But when great stress is applied slowly but relentlessly, toffee becomes taffy and ice
achieves the plasticity that permits it to flow down slopes, over boulders and around bends.
Movement is verrrrrry slow.
For example, Hubbard Glacier is the largest “calving” glacier in North America. When an
ice crystal falls atthebeginning oftheglacier intheStElias Mountains itwill take 400years
to make a journey of 122 km /76 mi to Disenchantment Bay in Alaska. Along the way it will
have joined up with a whole bunch of other crystals. Together they will leap into the ocean
as a calving iceberg the size of a 10 storey building.