The Life Cycle of Mountains

To most of us, mountains seem to be the epitome of long lasting permanence. Yet in geological time, they are fleeting and short lasting.

There are three main ways that mountains are created. The first is through plate tectonics. When one crustal plate slams into another, it may cause the formation of mountains through a process called upfolding or upthrusting. Basically this is similar to pushing two sides of a blanket together so that it bulges up in the middle.

An example of this sort of mountain building occurred about 50 million years ago when the India plate collided with the Asia plate. The uplift and upfolding resulted in the formation of the Himalayas at the northern border of India. Since this amount of time is a bare instant in geologic time and has not yet stopped, the Himalayas are still growing higher. As a general rule, the tallest mountains are also among the youngest, and this is true of this mountain range, which contains many of the world’s tallest mountains (measured from sea level) including Mt. Everest.

The second type of mountain formation is volcanic. While upthrust mountains tend to be jagged and rugged, volcanoes tend to be more even and more cone shaped. Examples of volcanic mountains include the islands of Hawaii and Japan, and the Cascade range in the Pacific Northwest, which include mountains such as Mt. Saint Helens, Mt. Hood, and Mt. Shasta.

The third type of mountain formation comes from what is called intrusion. In this kind of mountain building, a rocky substance such as salt, that has a lower specific gravity than surrounding rocks, forces itself upward because of the lower specific gravity, creating a bulge. These are usually large mounds that are often very even in appearance. An example is Ayers Rock in Australia.

The interesting part is that the moment that mountain formation begins, the mountain begins to be destroyed by the forces of nature. Wind and rain tear at the exposed rock, tearing it down into smaller and smaller grains. Rivers, streams and the ocean batter against the rock of the growing mountains, with the same results as with water erosion. Freezing water that has seeped into the rock, and plants that send roots into small cracks, also break down the rock. Eventually, the mountain is so ripped asunder that there may be little sign that there were originally mountains in the area.

At one time, the mountains of Appalachia, and those of Greenland, were tall and jagged, rivaling the Rockies of today. Now they are worn away. Eventually, no mountains will exist there at all. This has happened in many places in the world, many times, and the process continues today.

It is often hard for people to grasp this, because the time frame, though short in geological terms, is very long in human terms. Yet we can see the process of formation and destruction on Earth today. It is interesting to consider what the future mountain ranges of the world will look like, but it is likely that they will follow the same pattern they’ve been following for billions of years. They will at least look similar to what we are used to.