Geology Home Page physical geology historical geology planetary gems
Roger Weller, geology instructor
by Sara Borowiec
Alaskan Glaciers and more!
The state of Alaska is known for its fantastic fishing, beautiful scenery, and most of all, the phenomenal glaciers.
Alaska has more than 100,000 glaciers, however only about 650 have been given names. Below are six popular glaciers to visit!
1)The Mendenhall Glacier
2)The Hubbard Glacier
3)The Columbia Glacier
4)The Portage Glacier
5)The Matanuska Glacier
6)The Exit Glacier
In the modern world, roughly about 10% of land is covered by
glaciers. With the United States being covered with 75,000 square kilometers of
glacier, almost all of these glaciers are located in Alaska. The glaciers have
to be good for something! Alaska and Washington are the only two states that get
a significant amount of their water supply from their glaciers.
A glacier is defined as an extended mass of ice formed from
falling snow that has accumulated in a valley or mountain. Research has shown
that a good amount of Alaska’s glaciers have been retreating over the past
century, and that this process has actually sped up more recently.
There are two special types of glaciers; alpine and
continental. Alpine glaciers are caused predominantly by ice flowing down a
mountainous area, forming a ‘tongue’ of ice to the plains below. Continental
glaciers are mostly self-explanatory; an ice sheet found only in high altitudes.
Below are photos of both alpine and continental glaciers.
The blue hue that you see in glacial ice is caused by density.
Glacial ice becomes denser over time. When glacial ice becomes extremely dense,
the ice begins to absorb all colors in the spectrum and thus, reflects the color
blue. You can tell that there are many tiny air bubbles in the ice when the
glacial ice appears white instead of blue.
How do glaciers affect land? Of course glaciers transport
material as they move, but they also eat away at the land underneath them. Over
hundreds and thousands of years, glaciers can completely change the face of this
land. Glacial erosion is another movement that greatly affects land, causing
glacial valleys. These phenomena have steep, vertical cliffs where entire
mountainsides can be taken out.
Glaciers of course leave behind anything and everything that
they have successfully picked up, which can include huge rocks. Known as erratic
boulders, these rocks might seem completely foreign, because glaciers have
literally moved them hundreds of thousands of miles away from their home source
before they melt away.
Drumlins are long, tear-drop-shaped sedimentary
formations. What caused drumlins to form is a mystery, however scientists
believe that they were created subglacially when ice sheets moved across the
landscape during various ice ages. There are many different theories suggesting
where drumlins come from. It is suggested that they might have been formed in
the process of eroding the underlying land, or from desposing of sediments from
glacial water. Often times, hundreds to thousands of drumlins are found in one
place, having very interesting shapes when seen from above.
Glaciers can sometimes retreat or advance, moving in
any direction. Whichever way the glacier moves, no matter what, it is still
moving downslope one way or another. They can even move several meters in just
Glaciers definitely do not live an unnoticed
existence. There are many elements that contribute to glacier formation and
growth. Snow fall in the accumulation area adds to the glacier's mass. As the
snow slowly evolves and changes to ice, the glaciers weight takes a turn for the
heavier, forcing glacial movement. Further down the glacier is where most of the
melting and evaporation happens. Between these two areas is a median, where
snowfall sits and eventually melts.
Obviously, glaciers are notorious for their unique
visible features. These features can range anywhere from crevasses to a
discoloration in the ice. A crevasse is defined as when a glacier flows rapidly,
giant cracks called crevasses are created, which can make traveling across
glaciers quite dangerous. Underneath the glacier, large amounts of rock and soil
are ground up by the tremendous weight of the glacier.
Another common glacial feature is a moraine, which is created when the glacier picks up rocky debris as it moves. These long, dark bands of rocks and other materials are visible on top and along the sides of glaciers. There are three different types of moraines: Medial moraines run down the middle of a glacier, lateral moraines along the sides, and terminal moraines are found at the terminus (snout) of a glacier. Sometimes one glacier flows into another, creating combined wider moraines.
Do glaciers pose a threat? Most of the time, glaciers are found in far away, mountainous areas. Although this is the most common case, there are some that are found near cities or towns and sometimes present a threat for people living nearby. On land, lakes formed on top of a glacier during the melt season may cause floods. At the terminus of a valley glacier, ice falling from the glacier presents a danger to hikers. When ice breaks off over the ocean, an iceberg is formed, causing threats to ships or boats.
Glaciers may not pose a threat, but they can cause
many different phenomenons such as avalanches. Avalanches from glacier teminus’
have been recorded in the Swiss Alps for thousands of years, yet they still
happen despite several attempts to prevent them. Avalanches can have many
different causes such as snowfall, snow compaction, yelling while skiing or
climbing a snow packed mountain, or even weather and temperature. Although these
are all very effective causes of avalanches, the main cause lies within the snow
compaction. When the snow becomes too compacted, it is under a great amount of
stress. Anything as little as some snow fall can cause too much stress and thus,
cause an avalanche.
In conclusion, Alaskan glaciers are beautiful, fascinating works of nature, not to mention the beautiful Alaskan landscape surrounding them. Although glaciers may pose threats, they also benefit us with water, and many other useful resources.