The Power of Ice

Although its best use is cooling a good beer, ice in volume can make one heck of a nice looking landscape.  In the U.S., Glacier National Park is one of the world's great examples of a terrain created by ice.  Nearly every valley, peak, waterfall, and lake is a product of huge rivers of ice that flowed down from the mountains 20,000 years ago.  These ice rivers, called alpine glaciers, formed from years of snow accumulation that gradually compressed to ice and began to flow slowly downslope.  Ultimately the glaciers of Glacier National Park filled the existing stream valleys to thicknesses of 2,000 feet or more.  By about 12,000 years ago, the ice began to melt faster than the snows at the peak accumulated and the glaciers completely disappeared. (Glacier National Park currently has several small active glaciers, but these formed during a brief cold interval that began in the 1600s and ended by 1850).  

Unlike running liquid water, frozen water is capable of plucking massive volumes of large rocks from walls and bottoms of a valley, and using the rock fragments like an ultra-coarse sandpaper to grind away even more rock.  The end result is a rugged landscape with sheer valley walls, shapely pointed peaks called horns, knife-like narrow ridges called aretes, and broad, U-shaped valleys.  The glacier carries its load of rock down the valley and eventually dumps it at the edge of the mountains into a huge pile of gravel and boulders known as a terminal moraine.  At Glacier National Park, the underlying rocks also aided in the formation of the rugged landscape.  Many mountain ranges are underlain by granites or similar rocks which are very hard and difficult to erode; however, the rocks at Glacier are relatively soft ancient limestones and shales that are easier for the ice to attack and erode.

All of the classic terrain features that geologists now recognize as created by alpine glaciers can be found in Glacier National Park.  The picture above is Dusty Star Mountain on the east side of the Park, which is a textbook example of an arete.  The narrow knife-edge ridge formed when glaciers flowed down the valleys on either side of the mountain.  These two small, or tributary glaciers, joined with a large, or trunk glacier, in the valley that runs across the center of the picture.  The trunk glacier was also responsible for creating the nearly vertical face at the end of Dusty Star Mtn.  The ice, with its load of rock acting like giant sandpaper, simply shaved off the end of the mountain! 

Although Glacier National Park no longer has large active alpine glaciers, futher north in the Rocky Mountains of Canada at Jasper National Park, alpine icefields and alpine glaciers still exist.  Although most alpine glaciers occur at high elevations and are hard for anyone but die-hard mountaineers to reach, Athabasca glacier flows out of the Athabasca Icefield and is easily visited.  Although small compared to the ancient glaciers, Athabasca is still 1,200 feet thick at the second step.  At the base of the glacier, the dirty gray color on the ice is rock melting out of the ice.  The small piles gravel and rock just behind the RVs are part of a small  terminal moraine that formed when the glacier front remained stable for a number of years before melting back toward the mountains.  Although the front of the glacier is retreating due to faster melting, the ice is still flowing down from the icefield (top of photo) at a rate of a foot or so a day.

The ice on the surface of the glacier, about midway up probably fell as snow on the icefield 200 to 250 years ago, which makes it a young glacier--glaciers in Antarctica and Greenland have persisted for as long as 100,000 years!  

Glaciers are not smooth at all--in fact they can be downright dangerous.  Because the ice is very slowly, but steadily moving, the surface is prone to cracking--forming crevasses sometimes 100's of feet deep.  Meltwater also runs across the surface in summer and forms fast moving streams that flow into crevasses.  On the day we were on the ice at Athabasca, it was warm and several soft areas of ice had melted into 1-2 ft deep slush puddles that were difficult to see. 
And yes, the geologist in me could not resist -- I sampled the melt water.  A bit gritty, but cold and fresh otherwise. 

Until next time, enjoy the pics, and I 'll enjoy a beer.