Of the many processes which shape the crust of the Earth, the movement of glaciers is one of the most fascinating and important in relation to human habitation and the environment. Some of the most fertile farmland in the world resides in areas once covered by ice, and the effect of melted glaciers is very intricately linked to world sea levels.
The Physics and Chemistry of Glaciers
Technically speaking, ice is a rock. By definition, a rock is a mass of minerals. Since minerals themselves are defined as naturally occurring, inorganic, crystalline solids, ice falls into the rock category, being a mixture of solid water, a variety of sediments, and varying crystalline structures. Ice is similar to igneous rocks in that it is formed from a liquid, similar to sedimentary rocks in that it is deposited in layers by atmospheric processes, and similar to metamorphic rocks in that it can be transformed by crystal re-structuring under great pressures.
There is a common misconception that ice moves as a fluid. While this is partially true, it is not entirely representative. The movement of glaciers is primarily a function of tiny movements caused by the slight slip of individual grains, which differs from the molecular movement of “normal” fluids. The great weight of overlying ice is the cause of these slips. Therefore, the thickness of the ice, along with the angle of the slope, determines the flow of the glacier.
In addition, solid water under great pressure can become a liquid even if it is below its sea level freezing point. This is the same process that allows ice skates to glide across an ice rink, producing a thin layer of melt underneath the glacier and increasing the flow speed along the bedrock.
Glacial Erosion
Glaciers pick up a lot of debris in their continual movement downhill. This debris can be ground up like a fine flour or as large as a building, exemplifying the great forces at work in an icefield. Much of Northern Europe, Siberia, Canada, and the Northern United States are peppered with glacial debris from the previous sequence of ice ages. Glaciers have just as much erosive ability as running water since they can engulf boulders in their solid framework and crush them on the bedrock surface below.
The material does not settle out as it does in water, but continues its journey downhill, picking up other material all the way. This leads to the depositional stage, at the terminus of the glacier. Meltwater begins to “release” the suspended load, leading to complex braided river channels and melt ponds, exhibited in many parts of Canada and Siberia.
The characteristic jagged shape of large mountains is almost entirely attributed to the action of glaciers on their slopes. As a general rule of thumb, V-shaped valleys are a result of river processes, while wide U-shaped valleys are the result of glacial processes. Therefore, it is sometimes possible to determine ancient flow of glaciers by the sediments and terrain shape of the present.
Glacial Effects on Global Sea Level
It is estimated that ten percent of Earth’s land mass is covered by ice. This is primarily Antarctica and Greenland. This number also seems to be shrinking, leading to increasing concern about sea level changes around the world. Since a large portion of Earth’s population lives in coastal regions, the habitability of these areas may be at significant risk.
Many researchers have concluded that global temperatures are rising more rapidly than expected for a typical inter-glacial period, increasing the likelihood of continental glacier melt. Since ice in the Arctic does not sit on top of land, sea level changes from Northern melt would be negligible. However, it is estimated that the melting of all of the continental ice in Antarctica and Greenland would lead to a sea level rise of 210 feet globally, a truly catastrophic number which would inundate many of the largest cities in the world.
This is a highly unlikely event, and warming of this magnitude would certainly lead to many other serious problems for life on Earth. Even a nominal amount of glacial melt can lead to significant sea level increases, and the complex nature of atmospheric and oceanic circulation patterns could be heavily affected by the large influx of freshwater.
Sources:
Earth, 4th Ed., Frank Press and Raymond Siever, WH Freeman and Company, New York, 1986
Jarod Rhoades - Jarod is a musician and writer who resides in the beautiful Pacific Northwest. While his main focus is creative writing, he also churns ...
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