Cochise College           Student Papers in Geology

Geology Home Page                   physical geology  historical geology  planetary  gems           

Roger Weller, geology instructor

wellerr@cochise.edu

glaciers
by Juan Franco
Physical Geology
Spring 2011
               
 

Glaciers
 

            Glaciers are large, natural accumulations of ice, advancing, retreating, or standing stationary on the land.  A glacier forms where the annual snowfall, on the average, exceeds the amount of snow and ice lost by melting during the warm season.  At such a place a large snow field is created, and the region is known as one of permanent snow.  Snow fields lie at elevations varying from about sea level in Polar Regions to more than 18,000 feet in equatorial areas. (New Standard Encyclopedia, Volume 5)
 

            Each year a layer of snow is added to that already accumulated.  Gradually, the fresh snow is compacted and changed into a granular ice called a névé or firn. Later it is compressed by the weight of overlying layers into hard, crystalline ice. Eventually, in response to gravity and the weight of snow above it, the ice begins to move slowly downhill, and an active glacier comes into being. (New Standard Encyclopedia, Volume 5)
 

            Glaciologists usually recognize two distinct types of glaciers. The two main types are valley and continental glaciers.  A valley glacier is a glacier that forms in a mountain valley. (See figure 1)  A continental glacier is a glacier that covers a major portion of a continent or landmass, such as Antarctica. (See figure 2)

















Description: Photo: Antarctic ice sheet












 




 

Description: http://www.swisseduc.ch/glaciers/glossary/icons/valley-glacier.jpg

                               

                                                           

A glacier moves in much the same manner as a river. Although it appears to be rigid, a glacier can follow an irregular valley, moving around bends and even pressing through narrows. Such movements are possible because the tremendous pressure on lower layers causes the ice to become almost plastic when necessary.  At the same time, stresses are created in the glacier’s upper layers that result in formation of deep crevasses.  (New Standard Encyclopedia, Volume 5)
 

            The speed of a glacier is mainly governed by the steepness of its slope and the amount of ice issuing from its source.  Some glaciers have little or no movement; others have advanced 30, 50, and even 100 feet per day.  All parts of a glacier, however, do not move at the same speed.  Largely because of friction with the earth, the bottom and sides move less rapidly than the middle and surface sections.  (New Standard Encyclopedia, Volume 5)


            The melting and evaporating of a glacier’s surface, called ablation, follows exposure to sun, rain, or warm dry wind. The water, called meltwater, runs over the surface streams, pools, waterfalls, and deep potholes of swirling water, or moulins.  Melting also occurs within the glacier, especially at the bottom where friction with the earth is greatest.  As a result, subglacial tunnels and streams develop.  They collect water surface draining down through crevasses, make their way to the foot of glacier, and flow out through openings called glacier snouts.  (New Standard Encyclopedia, Volume 5)
 

Description: http://skywalker.cochise.edu/wellerr/vrtglg/ca-yosemite/6trip-yosemite2.jpgGlaciers are powerful forces and are capable of great erosive work.  On lowlands, they tend to level the surface; in mountains, where the ice is not thick enough to override the higher peaks and ranges, they make the terrain more rugged. Glacial ice is heavily laden with rock fragments, both large and small.  This material comes from the rock floor upon which the ice moves or from the valley walls. Under the great weight of the glacier, the land is slowly eroded by the grinding and scraping action of the ice itself. Deep grooves and scratches, called striations, can still be seen in most areas that were once covered by glaciers.  (New Standard Encyclopedia, Volume 5)  Glaciers also tend to cause glacial grooves and glacial polish.  Glacial grooves are formed as a glacier moves across bedrock, the large rocks that the glacier is dragging along gouge long grooves. (See figure 3)  Glacial polish occurs when a glacier moving across a bedrock surface polishes the bedrock by abrasion with the fine rock material that is embedded in the ice. (See figure 4)


Description: http://skywalker.cochise.edu/wellerr/vrtglg/ca-yosemite/6rip-yosemite3.jpg























          
 

While wearing down old landforms, glaciers are actively forming new ones elsewhere, either by the direct action of the ice or by the water issuing from it. There is a continuous process of eroding, transporting, and depositing the glacial material, or debris.  (New Standard Encyclopedia, Volume 5) 
 

Some landforms that are created as a result of a glaciers’ great erosive work include arêtes, cirques, drumlins, hanging valleys, and horns.

Arete

An arête is a skinny mountain ridge shaped on opposite sides by a series of glacial cirques.

 

Cirque

A cirque is a scoop-like depression on the side of a mountain formed by a valley glacier eroding the mountain.

 

Description: http://skywalker.cochise.edu/wellerr/physglg-draw/glaciers/6arete.jpg

 

 

 

 

 

 

 

 

 

 

 

 

 

              

           

Drumlin

A drumlin is a long, skinny, cigar-shaped hill that has been sculpted by a glacier flowing over it.



 

Description: http://skywalker.cochise.edu/wellerr/physglg-draw/glaciers/6drumlin.jpg

 

 

 

 

 

 

 

 

 

 

 

 

Hanging Valley

A hanging valley is a small U-shaped glacial valley exposed on the upper side of a larger U-shaped glacial valley.




 

Description: http://skywalker.cochise.edu/wellerr/physglg-draw/glaciers/6hanging.jpg

 

 

 

 

 

 

 

 

 

 

 

 

 

            (Diagram courtesy of R. Weller)

 

 

Horn

A horn is a mountain with very steep slopes which was carved with cirques on three or more by valley glaciers. Of the most famous horns, the Matterhorn in Switzerland is the most prominent.


Description: http://robyjen.com/images/europe/switzerland/matterhorn1.jpg



 

 

 

 

 

 

 

 

 




 

 

 

Glaciers are found on all continents except Australia, and on many islands.  In Europe mountain glaciers cap the Alps, Caucasus, Pyrenees, and ranges of Scandinavia. The Rockies and various coastal ranges in western North America carry hundreds of glaciers.  Glaciers are found on the summits of the Andes, in South America; the Himalayas, Karakoram, and other great Asian ranges; the mountains of New Zealand; and the volcanic peaks of equatorial Africa. Largest and most spectacular of all are the continental glaciers on Antarctica and Greenland.   (New Standard Encyclopedia, Volume 5)
 

Glaciers can be destructive and erosive forces, but despite that fact without glaciers we wouldn’t have or be able to enjoy the many wonderful scenes and extraordinary range of landforms found on our planet.

 

 

Works Cited

New Standard Encyclopedia, Volume 5. Standard Educational Corporation, Chicago.

http://skywalker.cochise.edu/wellerr/GLGP-illvocab/GLGP-12.htm

 

Photo Credits

Figure 1

http://www.swisseduc.ch/glaciers/glossary/valley-glacier-en.html

Figure 2

http://www.uwsp.edu/geo/faculty/lemke/geog101/lectures/24_glacial_landforms.html

Figure 5

http://robyjen.com/images/europe/switzerland/matterhorn1.jpg