Mountain Building: How Mountains are Made
When convergent plates collide, the lithosphere thrusts upwards to build mountains.
This geologic process of vertical upheaving are the orogenies or mountain building events.
Since the beginning of Earth, plate tectonics have carved out chains of mountains reshaping the landscape inside-out.
While young rock appear and disappear, cratons are stable pieces of continent that have lasted over 1 billion years old.
Plates push into each other at convergent boundaries
When two plates collide into each other, it’s at these continental collisions where mountains likely form.
At these convergent plate boundaries, it causes massive amounts of lithosphere to get subducted onto or under one another.
Throughout geologic history, Earth has experienced repeated periods of crustal movements and folding.
These mountain building events are orogenies that can take tens of millions of years to deform the lithosphere.
Anatomy of an overthrust fault
Faults take millions of years to fold, fault and overthrust. During this process, erosion constantly wears away at the mountain building event.
1. First, two layers of rock are built with many strata of sedimentary rocks.
2. Next, plate movement puts lateral pressure making the rock layers to buckle.
3. Then, the rock layer begins to fold over due to the tremendous stress. As the rock strata doubles over, it forms a fault.
4. The break completely folds east strata beneath the west strata.
5. Finally, erosion wears away as remnants of the overthrust and all layers are visible.
Examples of mountain building orogenies
You can find examples of orogenies wherever you see mountains around the world. And at the same time, you have erosion wearing it away fairly quickly.
For example, the Nazca and Antarctica Plate have uplifted the Andes mountain range. This mountain range is the longest in the world extending across Venezuela, Colombia, Ecuador, Peru, Bolivia, Chile and Argentina.
Another example is the Appalachians which run 1500 miles from Alabama to Maine. When Africa collided with North America, the Appalachians used to be 5 miles higher. But over 300 million years, weathering and erosion have torn them down. One after another, the building of North America is a series of orogenies. But the oldest rock is found in cratons, such as in the Canadian shield.