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5 Questions about Glaciers

By Edited Jun 20, 2015 0 0

Question #1. How are Glaciers Formed?

Snowflake?

Photo credit: biggertree on Flickr

Simply put, glaciers form from ice, which forms from snow. Snowflakes, which are lovely six-sided crystals, melt just a little, especially their extremeties. With a little condensation, they become little ice pellets. As te ice pellets stick to each other, firn is formed.[5531] Firn is the beginning of glaciers. Once firn gets to a thickness greater than 50 meters, the sheer weight of it compresses the ice enough to form a solid interlocking mass of ice.

Question #2. What are the Two Types of Glaciers?

Glaciers are divided into continental and alpline. Continental glaciers are much bigger. They can be more than 50,000 square kilometers in area, can cover entire continents, and have thicknesses greater than 1 kilometer!

Antarctica and Greenland are the two continental glaciers in the world today. Antarctica's ice sheet is one and a half times bigger than the continental US. It is the largest fresh water reservoir in the world and is more than 4000 meters thick. Greenland is much smaller, but still covers more than 1.5 million square kilometers.

Glacier from Gornergrat

Glacier from Gornergrat by roger4336 on Flickr

There are 67,000 alpine glaciers world-wide. They are found on top of mountains, thus the name. Sometimes, the glaciers are found in valleys. Alpine glaciers are prominent in Europe, especially in the Alps.

Question #3. How do Glaciers Flow?

According to Bill Deane,[5532] Geology Instructor, at the University of Tennessee, a glacier is defined as a thick ice mass formed from the accumulation, compaction, and recrystallization of snow that flows. Glaciers must flow or they are just blocks of ice. The average velocity of glaciers is 3 to 300 meters each year.[5531] But, how do they flow? 

glacier bay alaska

Photo credit: tyler corder on Flickr

Glaciers form as a series of layers. Each layer is tightly bonded, but between each layer there are weak bonds. So, the ice moves. The flow is greatest at the center of a glacier, and least at the sides and bottom of one.[5531] Why? There is less friction in the center, it is just ice on ice, not ice on rock like on the sides.

Glacial flow was first proven between the years 1874 and 1882.[5532] On the Rhône Glacier in Switzerland, stakes were put in a straight line across a glacier and checked regularly. By 1882, they had moved. 

Question #4. How do They Change the Earth?

Cervino (Matterhorn)

The Matterhorn Photo Credit: Garaigoikoa

Glaciers are the pre-eminent former of our landscape.[5531] Without glaciation, there would be fewer jagged peaks like the Matterhorn in Switzerland, no U-shaped valleys, no Norwegian fjords or moraines in Denali National Park, and no Great Lakes along the northern border of the US.

There are two main processes at work: plucking and abrasion[5532]. Plucking occurs when pieces of rock are plucked off the landscape by the glacier. With enough accumulation of these, the glacier forms a giant piece of sandpaper. Then, you get abrasion. U-shaped valleys are a direct result of these two geological processes.[5531] Water erosion forms V-shaped valleys. Fjords, deep, steep-sided inlets filled with ocean water, are also formed directly from glaciers. They are the visible sides of underwater U-shaped valleys. Horn, like the famous Matterhorn, are formed by erosion by several glaciers at once.

What about the Great Lakes? They, too, were created from glaciation. The Laurentide Galcier carved out massive valleys. As the ice retreated, the remaining huge blocks of ice melted. This meltwater filled the huge craters left by the retreating glacier, this forming the Great Lakes.[5533]

Question #5. What are Moraines?

View beyond Moraine Lake, Yukon, Canada

Moraine Lake, Yukon, Canada Photo Credit: shoops2011 on Flickr

Moraine comes from the French word morena, which means heap of earth[5531]. That's pretty much what moraines are - debris deposited by glaciers. A terminal moraine, aka end moraine, forms at the downhill end of a glacier. Ridges of debris that are parallel to the flow of the glacier are called lateral moraines and form up on the sides of the glacial valley. If two glaciers join, the lateral moraines that meet where they intersect may come down the middle of the new larger glacier and form a medial moraine. The North American continent is filled with moraines, especially the crescent looped moraines found throughout Canada and the northern part of the US.

Glaciers are a fascinating subject. Many scientists spend their entire careers studying glaciation. I hope this article has given you a glimpse into the amazing world of glaciers.

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Bibliography

  1. EE Larson, PW Birkeland Putnam's Geology, 4th edition. New York: Oxford University Press, 1982.
  2. Bill Deane "Glaciers and Glaciations." web.eps.utk.edu. 30/October/2012 <Web >
  3. "How the Great Lakes were Formed." msue.msu.edu. 30/October/2012 <Web >

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