Lesson #3 Content Center
The great mountain ranges of the world were created because of the constant but very slow movement of the Earth's plates. When the plates of the Earth collide the crust folds into high mountain ranges. The roots of the world's great mountain ranges contain some of the oldest rocks on the surface of the Earth. Some of these rocks are over 3.5 billion years old!! These rocks were once buried deep inside the Earth and have been raised into mountains by the collisions of the plates.
These plates travel at a very slow rate about 1 to 4 inches per year. The Indian Subcontinent was a very fast mover, clipping along at over 4 inches per year. When it slammed into the Eurasian plate over 24 million years ago the collision built the highest mountain range in the world, the Himalayas. In fact, the Himalayas are still climbing higher and higher today.
How many miles would a plate travel in 100 million years at a rate of 1 inch per year? (Hint: Divide 100,000,000 inches by 12 inches per foot and then divide that answer by 5280 feet in a mile). Answer- In 100 million years the plate would travel about 1578 miles.
There are five ways that mountains are formed
- Volcanic activity
- Dome building
In this lesson we are going to concentrate on the processes of 1)Folding, 2)Faulting, and 3)Dome building.
All rock that is put under extreme pressure for long periods of time (thousands or millions of years) will fold like clay. Folding is a process in which the Earth's plates are pushed together in a roller coaster like series of high points and low points. Folding bends many layers of rocks without breaking them. The Appalachian Mountains and Rocky Mountains of the United States, and the Alps of Europe are examples of mountain ranges that were formed by folding.
Folded Strata (Layers)
Many of the greatest mountain ranges of the world have formed because of enormous collisions between continents. The Appalachian Mountains in the Eastern United States were formed about 400 million years ago when North America and Africa collided.
400 million years ago
The areas (next page) represented in yellow (white) are major mountain ranges that were formed by collisions of the continents millions of years ago!!!
Mountains sometimes form when many layers of the Earth's crust are moved vertically upward at fault lines by pressures caused by plates colliding. Fault lines are great cracks in the crust. The mountains that are formed in this way are called fault-block mountains. The Sierra Nevada mountains in California and Nevada, and the Grand Teton range of Wyoming are examples of fault-block mountains.
The Black Hills of South Dakota and Wyoming, and the Adirondack Mountains of New York are low mountains that were formed when the crust was heaved upward without folding or faulting into a rounded dome. These are called Dome Mountains. Dome mountains are much higher in elevation than the surrounding land and because of this erosion occurs at a very fast rate.
Thought and Discussion Questions
- What are the 5 causes for mountain building?
- What is the difference between how folded mountains and block-fault mountains are formed.
- How do dome mountains form?