Why do mountains have to be so high?
Hiking down from 15,000 feet in the Bolivian Andes mountains to our mineral exploration base camp at 13,000 feet, I was thinking; “Why do mountains have to be so dang high? Why aren’t they only 6,000 feet like the Cerbat mountains near Kingman?” As a matter of fact, the highest point in the Andes, Mount Aconcagua, is only about 21 feet lower than Mount Everest. My head was already hurting from lack of oxygen and now with these thoughts taking up more oxygen, I was miserable.
Gravity works on everything and exerts a force trying to keep it all at its lowest point, in relation to the center of the earth. There has to be something to counteract this force to make things not be flat. On the earth’s surface we have various events that make mountains stand higher than the surface around them. Volcanic eruptions spew lava and form tall mountains such as Mount Rainer in Washington. Faults push some blocks up and others down, like in the Basin and Range province of the American southwest. But the highest mountains in the world are at junctions where two geologic plates bumped into each other. In the case of the Himalayas, it’s the subcontinent of India bumping into the Tibetan Plateau of Asia. In the case of the Andes, it’s the South American plate bumping into and overriding the Pacific Oceanic plate. This “bumping” action is ongoing because the plates are still moving, causing the mountain ranges to still be going up. But how can this be, isn’t rock solid? How can huge chunks of rock be moving sideways and up and down?
The earth is constantly moving- albeit very slowly. This movement has different effects. California residents are well aware of these effects. When the San Andres fault moves- EARTHQUAKE. An earthquake is a brittle type of movement when two plates move in opposite directions. The rocks can only take so much stress until they break and violently move causing shock waves called “S” and “P” waves. We have all seen pictures or have actually felt the results of these waves. When I was working in Chile, it was almost a weekly occurrence to feel small earthquakes. They were so common that no one paid attention to them.
What happens down deep below the surface when the movement is slower is different. Given enough time and pressure, the rocks can flow. If you’ve ever played with silly putty, you know that if you slowly pull on the putty, it stretches. If you pull quickly, it breaks. This is similar to what happens to rocks. Near the surface, rocks break; at depth, they stretch.
The shape of the mountains gives us a hint as to what events formed them. Around Kingman we have fault-block mountains with abrupt sides that have a relative short length. These were formed by sudden breaks along faults caused by the pulling apart of the North American Plate. Some blocks went down, forming valleys and some went up, forming mountains- the Basin and Range province of the American Southwest.
The San Rafael Swell in Utah is a broad and relatively flat-topped uplift called an “anticline”. The sedimentary beds were pushed up by underlying rocks being compressed by an event called the Laramide orogeny (Laramide- a period in time; orogeny- a mountain building period).
The Andes mountains were formed by being pushed up as the South American continental plate was pushed on top of the Pacific Oceanic plate. In the case of the Himalayas, it was two continental plates bumping into one other and the rocks being pushed up. Mountains that are formed by geologic plates bumping into one another are as long as where the plates came together. In the case of the Andes, they are as long as the continent of South America. The Rocky Mountains are another range that were formed by the collision of two plates. That is why they’re so long.
At the foot of Aconcagua, 22,831 feet.
As I made my way down to base camp after taking rock samples from rugged outcrops, again talking to myself, I asked; why did the mineralized ground have to be at these high altitudes? Why couldn’t it be in some beautiful flat area that was easy to get to? It was at times like these I wondered why I went into geology and not some office job where it’s easy to breath. But then, who’s going to find the next gold strike? I better quit using up oxygen by thinking and save the few brain cells I have left. Tomorrow will be another day of hiking up and then down this Andean peak loaded with rock samples.
