Chapter 3: Mountains and Volcanoes
BIG IDEA: Mountains and volcanoes form as tectonic plates move.
KEY CONCEPT 3.1: Movement of rock builds mountains.
KEEP THESE QUESTIONS IN MIND:
1) How does the folding of rock form mountains?
2) How does rock movement along faults form mountains?
I. MOST MOUNTAINS FORM ALONG PLATE BOUNDARIES.
A. A shallow sea once covered Mt. Everest.
1. Rocks containing remains of ocean animals found there.
2. Rocks formed at a far away spreading center also found there.
3. How can this be? (Page 77)
B. MOUNTAIN RANGES AND BELTS
1. Mountain- an area of land that rises steeply from the land around it.
2. A single mountain is rare.
a. mountain range- long line of mountains formed at about the same time by the same processes.
b. mountain belt- ranges that are close together.
i. Most major mountain belts are located along tectonic plate boundaries.
ii. Some, like the Appalachians, are on the interior of the plates.
iii. These were formed by ancient plate collisions that formed the continents.
C. MOUNTAINS, ROCKS, AND SEDIMENT
1. Processes wear mountains down.
a. On the surface, water and wind break rocks apart and move the pieces away.
b. As long as mountains are pushed up faster than they wear down, they grow taller.
c. Young mountains are tall and steep.
d. Eventually water and wind take over, and over time the mountains become rounded hills.
e. The land becomes flatter as mountains wear down and valleys are filled with sediments. If tectonic plates stopped moving, eventually the surfaces of the continents would be completely flat.
II. MOUNTAINS CAN FORM AS ROCKS FOLD.
A. Tectonic plates move only a few centimeters a year.
1. Edges of a continent along a convergent boundary are subjected to high amounts of stress over very long periods of time.
2. Some rocks break, some fold.
3. folded mountains- mountains formed when continental crust crumples and bends into folds.
a. Form as an oceanic plate sinks under the edge of a continent or as continents collide.
b. The Himalaya belt formed by a collision between India and Eurasia.
B. The Himalaya mountain forming process. (page 80-81)
1. A convergent boundary develops.
2. Continental collision begins.
3. Collision continues.
C. Earthquakes can also be important to the upward growth of mountains (at reverse faults).
III. MOUNTAINS CAN FORM AS ROCKS MOVE ALONG FAULTS.
A. fault-block mountains- form as blocks of rock move up or down along a normal fault.
1. Forces within the Earth cause the lithosphere to stretch and pull apart.
2. Cold, rigid rocks in the crust break into large blocks.
3. As stretching continues, the blocks of rock move along the faults that separate them. (page 83)
B. The Sierra Nevada in California is a fault-block mountain range.
1. The range moved up along a normal fault on its eastern edge.
2. The block on the other side dropped down.
3. The eastern side of the range is steep. The western side tilts down gently toward California’s Central Valley.