A glacier is a moving river of ice and land. There are two types of glaciers:
Continental glaciers are massive amounts of ice that cover the entire continent
such as Antarctica and Greenland. 95% of ice on earth is locked up in continental
glaciers. Alpine glaciers like this one behind us are formed in mountainous
regions. This one here is the Franz Josef glacier in the South Island of New
Zealand. Most of New Zealand's largest glaciers are in the southern alps which have
the highest mountains and the biggest precipitation. Glaciers originate from
heavy snowfalls over a long period of time. When snow initially falls it has
many air spaces between the snow flakes. Over time the weight of new snow above it squeezes
the air out of the pore spaces and compacts the snow, just like me making
the snow ball. Eventually this compaction causes the snow to become ice. Because
the air has been squeezed out, the ice will turn a bluish color. Glaciers have
several components. The area where the snow falls is usually the part of the
glacier with the highest elevation and is called the zone of accumulation. Further
down the glacier is is the zone of ablation where most of the melting and
evaporation occurs. Here the ice shows a lot of crevices. The
end of the glacier is called the terminus or snout. At many glaciers there are glacial
lakes at the terminus.
A glacier will continue to grow as long as the rate of ice formation in the zone
of accumulation is greater than the rate of ice melting from the zone of ablation.
When more melting takes place than ice forming the glacier is said to be in
retreat. The Tasman glacier for example has been in retreat, causing the Tasman
Lake to grow increasingly larger. Back in 1973 this lake that not exist. Over a
single year a glacier may both grow and retreat, depending on the rate of
accumulation compared to the rate of ablation. This is called a glacial budget.
In times when global climate has been cooler glaciers have expanded. We call
these periods glaciations. Warmer periods have seen glaciers in retreat. We
call these interglacials. Now at this time in history glaciers are
in retreat. Where I'm standing here at the Franz Josef glacier, for thousands of
years was actually once hundreds of meters under ice. You can see
behind me this pool which is known as Peter's pool. It is what we call a
kettle pool. It is formed when a glacier that is in retreat
leaves behind a huge iceberg and eventually that iceberg melts and forms
this pool.
The tremendous weight of the ice combines with gravity to cause the glacier to
move. At locations where a glacier flows rapidly cracks called crevasses form.
Crevasses are very dangerous to climbers and should be avoided. The
terminus of the glacier is also very dangerous.
Now glaciers are notoriously dangerous for climbers as there is always the
ever-present danger of a rock slide or even like a big ice fall from the
glacier. A few years ago at Franz Josef glacier, a couple of huge house sized icebergs
actually fell on a couple Australians who got too close to the terminal face.
Now here at Fox glacier the Department of Conservation staff have
done some blasting up to the glacier to prevent a potential disaster. Soon we
should see a surge of water come down the glacial river.