What percentage of glaciers in the world are retreating?
100%! All the glaciers in the world are "retreating".
"Retreating" and "advancing" refers only to
the terminus or bottom end of a glacier. The retreating of glaciers
is caused by the warming of the globe. Overwhelming evidence shows
this warming is being caused or at least accelerated by the unnatural
release of greenhouses gasses by humans burning fossil fuels.
Can a glacier move forward and retreat at the same time?
Yes, amazing as that may seem. Retreating glaciers in fact do
move forward as ice moves downhill like it's on a very giant
and very slow moving conveyer
belt. As snow falls on the top of a glacier, the weight of the snow causes
the glacier to move forward. Further down the glacier is the "ablation
area", where the snowfall is equal to the snowmelt. Here the glacier
is in equilibrium. Whenever this area is disturbed by increased snowfall
or warmer temperatures, the glacier begins to advance or retreat respectively.
What is a crack in a glacier called?
A crevasse. Crevasses are one of the most dangerous aspects of a glacier.
Crevasses are created as the awesome forces caused by a moving glacier
deform and crack glaciated ice. These can be hundreds of feet deep and
are easily made invisible by being covered by snowfall on the surface
of a glacier. The inexperienced should never try to traverse a glacier.
They are very very dangerous.
What is moraine?
Moraine is the name given to rock and other debris pushed into piles by
a glacier. In Homer we landed on a lake that was formed by a giant end
moraine left by a retreating glacier. Falling rain and glacier run-off
was trapped by this moraine forming a lake.
What part of a glacier moves the slowest?
A glacier is slowest moving where it comes in contact with
the ground. This is actually a pervasive physical phenomena that
is also true about
other flowing mediums like air moving over an airplane wing or water
flowing down a river. This is referred to as a "boundary layer" in
move incredibly slowly or quite quickly depending on how you look at
it. One of my friends at the United States Geological Survey
threw a bear
transmitter into a crevasse on the Exit Glacier (we visit this glacier
on the "Seward" episode). Mapping the transmitter's movement
over the past few years has shown that the middle of this glacier is moving
forward at about 2 feet per day! Even though the middle of the glacier
is moving forward, the Exit Glacier is still "retreating" at
its bottom end.