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Plate Movements
(Lesson #3)
(Mountain Building)
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.
Math Connection
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
- Folding
- Faulting
- Dome building
- Erosion
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?
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