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Mountains
Most mountains are formed by Earth’s internal forces. Do you think all
mountains are the same? There are actually different kinds of mountains, formed
in different ways.
A major force, shaping land is uplift, the lifting of land by forces in the
Earth’s interior. Moving tectonic plates, lift land, forming mountains. Folded, faultblock and volcanic mountains all result from different types of plate movements.
Volcanic mountains are formed when magma, or molten rock, is forced out
through the crust. Volcanic mountains are most common at tectonic plate
boundaries. Hawaii’s islands were formed by volcanoes. They formed, not on a plate
boundary, but over a hot spot. A hot spot is a place where magma rises close to the
surface in the middle of a plate. The super-hot magma burns a hole through Earth’s
crust, like a blowtorch burns through metal. Then the magma rises through the
crust. It hardens on the Earth’s surface and forms a mountain.
Folded mountains are the most common type of mountain. The Alps, the
Andes, the Himalayas, the Rockies, and the Appalachian mountains are all folded
mountains. Folded mountains are formed when tectonic plates collide with each
other. The impact from the collision of two land masses causes the Earth’s crust to
fold or bulge upward. This process takes millions of years. The Himalayas formed
when the separate land mass of India collided with Asia. The pressure of the two
pushing against each other caused land to fold upward, forming the largest
mountains on Earth.
Plates are curved to fit the surface of Earth’s sphere. As the plates move,
the fit changes. Tension (force pulling or pushing on the plate) can cause the crust
to split, or fault. Mountains can form when blocks of Earth’s crust on either side of
a fault are dropped below or pushed above the surrounding land. This can happen
where sections of crust are pulling apart or pushing together. At these places,
large blocks of the crust are sliding up and down past each other. The blocks that
were pushed up form fault-block mountains. Examples of fault-block mountains
include the Sierra Nevadas of California, the Wasatch Range of Utah, and the
Teton Range of Wyoming.
Dome Mountains are formed when magma is trapped beneath rock. It tries
to rise to the surface but can’t break through. The pressure of the hot magma
trying to rise pushes up layers of rock. This forms a rounded mountain shape. As
the magma rises, it cools and turns into rock, or lithifies. The Black Hills of South
Dakota are examples of Dome Mountains.
Mountains Questions
1. Volcanic mountains are formed by:
a. the ash and smoke from a volcano
b. rock on Earth’s surface melted by a volcano’s heat
c. magma breaking through Earth’s crust and forming a mountain
d. rock being pushed up from below Earth’s surface
2. Which type of mountain is formed by two tectonic plates colliding?
a. volcanic mountains
b. folded mountains
c. fault-block mountains
d. dome mountains
3. Which type of mountain is formed when the crust breaks and large pieces of crust
are pushed up above the surrounding land?
a. volcanic mountains
b. folded mountains
c. fault-block mountains
d. dome mountains
4. Which type of mountains is formed when magma can’t break through the crust, but
pushes up the rocks above it?
a. volcanic mountains
b. folded mountains
c. fault-block mountains
d. dome mountains
5. Which of these is an example of a dome mountain?
a. Hawaiian Islands
b. Rocky Mountains
c. Sierra Nevada Mountains
d. the Black Hills
6. Which of these is an example of a fault-block mountain?
a. Hawaiian Islands
b. Rocky Mountains
c. Sierra Nevada Mountains
d. the Black Hills
7. Which of these is an example of a folded mountain?
a. Hawaiian Islands
b. Rocky Mountains
c. Sierra Nevada Mountains
d. the Black Hills
Mountains Answers
1. c
2. b
3. c
4. d
5. d
6. c
7. b