Mountains can form as rocks fold.
Though people usually do not think of rocks as being able to
bend and fold, they can. Think of a wax candle. If you bend
a candle quickly, it will break. If you leave a candle propped
up at an angle, over many days it will bend. If the candle is
in a warm area, it will bend more quickly. Rocks also bend
when stress is applied slowly. Rocks deep in the crust are at
high temperatures and pressures. They are particularly likely
to bend rather than break.
Under what conditions are rocks likely to bend and fold?
VOCABULARY
Make a word triangle
for folded mountain
in your notebook.
Remember that tectonic plates move only a few centimeters
each year. The edge of a continent along a convergent boundary
is subjected to stress for a very long time as another plate pushes
against it. Some of the continent’s rocks break, and others fold.
As folding continues, mountains are pushed up. A folded mountain
is a mountain that forms as continental crust crumples and bends
into folds.
Folded mountains form as an oceanic plate sinks under the edge
of a continent or as continents collide. One example is the Himalaya
(HIHM-uh-LAY-uh) belt, which formed by a collision between India
and Eurasia. Its formation is illustrated on page 257.
At one time an ocean separated
India and Eurasia. As India moved northward, oceanic lithosphere
sank in a newly formed subduction zone along the Eurasian Plate.
Along the edge of Eurasia, folded mountains formed. Volcanoes
also formed as magma rose from the subduction zone to the surface.
1
Convergent Boundary Develops
2
Continental Collision Begins
3
India and Eurasia continue to push together.
Their collision has formed the Himalayas, the world’s tallest
mountains. They grow even higher as rock is folded and pushed up
for hundreds of kilometers on either side of the collision boundary.
Eurasia is the landmass
consisting of Europe
and Asia.
Eventually the sea floor was
completely destroyed, and India and Eurasia collided. Subduction
ended. The volcanoes stopped erupting because they were no longer
supplied with magma. Sea-floor material that had been added to
the edge of Eurasia became part of the mountains pushed up by
the collision.
Collision Continues
Earthquakes can also be important to the upward growth of folded
mountains. A great deal of rock in the Himalaya belt has been pushed
up along reverse faults, which are common at convergent boundaries.
256 Unit 2: The Changing Earth