How mountains are created and destroyed
Living at the foot of Pikes Peak brings a sense of awe and wonder. The massive rise of the Front Range of the Rocky Mountains is and omnipresent symbol of the forces of geology. The colossal summit of these mountains, more than a mile above a city already more than a mile above sea level inspired Katherine Lee Bates to write about «purple mountains majesty» in her song «America the Beautiful».
But, just what was it that created these majestic peaks? What were the actual forces that are at work here?
The majority of the actions that create mountains are due to plate tectonics. The crust of the Earth is made up of numerous plates that move across the surface of the planet. Where these plates come into contact various forces and reactions create mountain ranges.
When two plates of continental material collide they buckle against one another creating massive ranges, like the Himalayas. The same event that created the Himalayas is believed to have also created the Alps, the Pyrenees and most all of the major mountain ranges of Europe, the Middle East and Southern Asia. In the case of the Himalayas the plates of Africa and India moved northward into the massive Eurasian plate. Since both plates were of similar makeup neither could be forced under the other causing the edges to buckle, just like if you push the edges of a tablecloth together towards the middle it will fold and bunch up.
This process is continuing today in some of the mountainous regions of Europe and Asia. However, the changes are so slow that we are unable to measure them. The building of mountains takes millions, or tens of millions, of years. Imagine the tallest mountain on Earth, Mt. Everest. At 8,848 meters above sea level, even if the mountain started at sea level, over ten million years it would have risen less than a millimeter per year to reach its present height.
When an oceanic plate comes into contact with another plate, whether it’s a continental plate or another oceanic plate, one of the plates goes under the other, creating a subduction zone. Oceanic plates are made up of basalt, a fairly dense rock. Continental plates are made up of granite, and the sedimentary and metamorphic products of granite, which are considerably less dense than basalt. Therefore, oceanic plates will always be driven under continental plates. In the case of contact between two oceanic plates there is no certainty as to which will go over and which will go under, but if they’re not sliding alongside one another, one