THE FORMATION OF MOUNTAINS

Introduction

No one defines mountains very carefully beyond saying that they are places which are higher than their surroundings. The reason for this is probably because it takes different things to make mountains in different places. In Montreal, "The Mountain" is Mount Royal, a place which stands about 500 feet above its surroundings. In Hamilton, "The Mountain" is the edge of a terrace which is only a few hundred feet high. In the Maritimes and Newfoundland it takes a thousand feet or so to qualify. But none of these would be much more than a slight rise if it were to be found in western Alberta or British Columbia where even the "foothills" are that high.

We can agree, however, that mountains are relatively high places and that, as a result, they are subject to erosion. Streams flow faster on them and cut deeper into them. In high mountains glaciers cut into the rocks and frost splits them apart. Landslides and talus slopes indicate more of the erosion that takes place there.

What makes the mountains high in the first place is not entirely understood. We can only say that great pressures in the earth's outer layers seem to buckle up great belts of the outer part of the earth's frame, wrinkling and breaking the rocks in some places, but only uplifting them gently in others. This means that the kinds of rocks and the kinds of structures within them will be different in different mountains.

Volcanic Mountains

Mountains are sometimes made by the accumulation of masses of molten rock and ash which pour out onto the surface of the earth. Sometimes these mountains are beautiful, symmetrical cones like Fujiyama in Japan, or Osorno in Chile. Some of them are in the sea and appear as islands when their tops stick out of the water as in the Hawaiian Islands and Bermuda. Others, like Etna and Vesuvius in Italy are less regular in their shapes.

Mountains by Subtraction

It is odd to note that the mountains which we look up to in our travels may be made by the subtraction of something rather than the piling up of something. Suppose an area were to be broadly uplifted so that a high, flat region resulted and then rivers were to cut deeply into the high plateau and cut it up. Eventually the region may be cut down to a much lower level with only a few high-standing remnants of the original highland left. These would appear as mountains. This subtracting effect is present in all kinds of mountains which have undergone erosion. Mountains which are made this way are usually composed of rocks which are harder than those which have been worn away.

Geosynclinal Mountains

When we approach a study of the origin of any of the great belts of mountains of the world, like the Alps, the Himalayas and the Rockies, we are at once impressed by their similarity of history. They all seem to have started with depression of long, trough-shaped areas in the earth's crust. This is exactly the reverse of what people would expect. Shallow seas spread into these very large depressions, which are called geosynclines. In North America we know of ancient seas in geosynclines which extended from what is now the Arctic Ocean, in the region of the Mackenzie Delta, all the way to California, and from Newfoundland to the Gulf of Mexico. Masses of muds, sands and silts poured off the surrounding land areas into these troughs. After many millions of years of such accumulation these sedimentary materials were tens of thousands of feet thick.

The ramparts of Mount Eisenhower overlook the valley of the Bow River and the Trans-Canada Highway in Banff National Park. The horizontal bedding of the sedimentary rocks combine with the vertical jointing to produce the pattern of erosion. Below the cliffs, talus slopes lead downward to the forested valley floor and the river which is carrying the wastes of the area towards the distant sea.

The reason for the next step in the formation of this kind of mountain system is not known. But it is known that great compression next caused the thick masses of sedimentary material to fold and fault, and then to be uplifted, sometimes many thousands of feet. At about the same time this was going on, great masses of molten, igneous material were intruded into the cores of the buckling masses of sedimentary rocks. After this, things quieted down and the slow processes of erosion cut into the masses of folded and intruded rocks. This is the present stage of development of our own Rocky Mountains and this is the kind of history that accounts for the scenery of Banff and Jasper National Parks.

Now, if the erosion keeps on for millions of years after this, the mountains will be gradually worn away. It may even come to the time when the whole area is once again reduced to sea level. Now another stage in the geosynclinal mountain story is reached, and another event takes place. This time the areas of old, eroded rocks with their deeply folded and faulted structures and their igneous cores, are uplifted. Rivers once again cut into the rocks below. It is not long before they find that some of the rocks are more easily eroded than others so that valleys are cut into the soft rocks and hills are made of the harder, more resistant rocks by subtraction.

This is the stage of development of the mountains of eastern North America where you can see the results of this history in the Appalachian Mountains. You can see them in the rolling hills of New Brunswick, where Fundy Park is located, and in Terra Nova Park in Newfoundland. You can see them in Cape Breton Highlands National Park, perhaps the best of all, for here much of the uplifted flat surface of erosion is still visible in the interior of the island where the park road is at an elevation of more than 1,400 feet. Here, too, you can actually descend the steep-walled valleys and clefts which are cut into the old surface, for the road follows them in its ups and downs in this beautiful country.

Mumm Peak at the head of Smoky River in Jasper National Park near Mount Robson, is made of tilted Cambrian sedimentary rocks with older rocks underlying them to the right in this view. The lower parts of the talus slope have become partly covered with vegetation but openings are maintained where snowslides sweep down the slopes and where pieces of rock and frost-riven fragments keep dribbling steadily down.

Conclusion

Once again we see that an understanding of scenery heightens beauty in the eye of the knowing observer, for he is able to appreciate that mountains are part of a vast picture of wearing away and replenishment, of uplifting and wearing down in a story of the earth's surface which is marked by system and order.