Familiar Talks on Science: World-Building and Life; Earth, Air and Water.

by Elisha Gray

In the downward flow of a glacier—slow as it is—there is an exhibition of wonderful power; great bowlders are torn from their beds and either ground to powder or carried down to the end of the glacier, to be dropped with the other débris that has been carried there by the same force, forming an accumulation that geologists call the "moraine." Of these moraines we will speak more fully later on.

It was the privilege of the writer some years since to visit the great glaciers of Switzerland and to some extent study their action. Some rivers have their origin chiefly in melting glaciers. They start as ice rivers and end in rivers of water. The effects during the great ice age of some of these glacial rivers, which are now extinct, are very remarkable; we shall have occasion to refer to them when we come to treat of the glacial period.

There is a glacial river flowing which is fed largely by the great Rhone glacier in Switzerland. The water from this river is almost as white as milk, which is occasioned by the grinding action of the great ice blocks on the rock as it flows down the sides of the mountain. These glacial rivers are much higher in summer, of course, than in winter, some of them having not only an annual fluctuation, but a diurnal one. The former is caused by the cold of winter, and the latter because it freezes to some extent at night and checks the flow of water. The difference between day and night in these high altitudes is very marked. While it is extremely hot in the sun, it is cool the moment we step into the shade.

I remember walking across one of the glaciers in the Alps, called the Mer de Glace, one clear day in summer, when I suffered so much from the heat, although standing upon a sea of ice, that it was necessary to carry an umbrella. In fact, during my stay there was a case of sunstroke that occurred upon this same glacier. This intense heat during the day melts the surface of the ice, which forms streams that run along on the top of a glacier until they come to a crevasse or riffle in the ice river, where they plunge down and become a part of the glacial stream that is flowing underneath the ice.

The speed at which these ice streams flow varies greatly with the size of the glacier as to width and depth and the steepness of the grade, and many other conditions. In its movement the glacier is constantly bending and freezing and being torn asunder by tensional strain, yielding and liquefying at other points by pressure, only to freeze again when that pressure is removed. This, taken in connection with the friction of the great ice bowlders, produces a movement that is exceedingly complicated in its actions and interactions.

According to Professor Tyndall's investigations, the most rapid movement observed in the glaciers of Switzerland is thirty-seven inches per day at the point of greatest movement. From this point each way the motion gradually diminishes until it reaches the sides of the glacier, where the motion is not more than two or three inches.

The great North American glaciers move at a much higher rate of speed. We are indebted to Dr. G. Frederick Wright, author of "The Ice Age in North America," who spent a month studying the Muir glacier in Alaska, for many details concerning that great ice river. This glacier empties into Muir Inlet, which is an offshoot of Glacier Bay. It is situated in latitude 58 degrees 50 minutes and longitude 136 degrees 40 minutes west of Greenwich. The bay into which this glacier empties is about thirty miles long and from eight to twelve miles wide. This bay, with its great glacier, has a setting of grand mountain peaks. I cannot do better than to quote the words of Dr. Wright when he describes the location of this glacier. Dr. Wright lived for a month in a tent on the edge of this bay, a short distance below the face of the great glacier, where the icebergs fell off every few minutes into the deep water.

He says: "To the south the calm surface of the bay opened outward into Cross Sound twenty-five miles away. The islands dotting the smooth surface of the waters below us seemed but specks, and the grand vista of snowclad mountains guarding either side of Chatham Strait seemed gradually to come to a point on the southern horizon. Westward toward the Pacific was the marvelous outline of the southern portion of the St. Elias Alps. The lofty peaks of Crillon, 15,900 feet high, and Fair Weather, 15,500 feet high, about twenty-five miles away and about the same distance apart, stood as sentinels over the lesser peaks."

The Muir glacier might be likened to a great inland sea of ice fed by many tributaries or ice rivers. It narrows up at the point where it empties into Muir Inlet to 10,664 feet, or a little over two miles. An enormous pressure is exerted at this point, which causes the ice to flow in the central portion at the rate of about seventy feet per day. There is a continual booming, like the firing of a cannon, going on, caused by the bursting of some great iceberg either before it takes its final leap into the water or at the moment of its fall. At the point where these great icebergs drop off into the water they stand like a solid wall 300 feet above its surface. Dr. Wright says: "From this point there is a constant succession of falls of ice into the water, accompanied by loud reports. Scarcely ten minutes, either night or day, passed during the whole month without our being startled with such reports; and frequently they were like thunder claps or the booming of cannon at the bombardment of a besieged city, and this though our camp was two and one-half miles below the ice front.... Repeatedly I have seen vast columns of ice extending up to the full height of the front topple over and fall into the water. How far these columns extended below the water could not be told accurately, but I have seen bergs floating away which were certainly 500 feet in length."

It is estimated that the cubical contents of some of these icebergs are equal to 40,000,000 feet. This great glacier is fed by the constant precipitation of snow upon the sides and peaks of the high mountains that surround its vast amphitheater, which is floored with icebergs. Wonderful as this seems to us to-day, it is scarcely a microscopic speck of what existed during the ice age all over the northern part of North America.