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CP Sci 9- 1st Sem.

Gen Chem - 1st Sem.

Where & How Mountains Form


    1.    Explain how some of Earth's mountain belts formed.

    2.    Compare and contrast active and passive continental margins.

Key Terms:

    mountain    continental margin

Notes (11-1)

As we discussed earlier, the Earth is undergoing constant change.  Changes are occurring as some plates diverge while others are converging.  The converging plates of the Earth are responsible for creating the world's mountain ranges.  A mountain is a large mass of Earth's crust that rises from its base.  There are several different categories.

Mountain Belts:

Mountain belts are formed at convergent plate boundaries.  

bulletMost mountains in the world were formed this way.
bulletNorth American Cordillera - Spans from Canada to Mexico (cascades are part)

North American Cordillera: northern Canada to northern Mexico

(www.stanford.edu/~dmiller/ WNAMcordillera.gif)

Continental Margins

A continental margin marks the boundaries of the oceanic and continental crust.  The continental margins are separated into 2 types, active and inactive.  Both inactive and active margins are responsible for supplying the mountain building  materials for the mountain belts.


bulletOccur at plate boundaries
bulletmountain building occurs in these regions - Pacific side of North & South America


bulletStable areas not at plate boundaries
bulletaccumulate sediments of dead organisms and eroded coastline - Atlantic side of North & South America

(dusk.geo.orst.edu/oceans/ images/calif.gif)


How mountains Form

Mountains are formed as a result of compression (convergent), tension (divergent) and shear forces (transform) that are constantly at work on the Earth through the moving plates.  These forces continually stretch and fold the rock creating the mountain belts deep within the lithosphere.


Deep within the lithosphere, pressure and heat deform rocks into folds.  The steepness of the folds indicates the intensity of the folding

bulletAnticline - up folding
bulletSyncline - down folding

(courses.smsu.edu/ejm893f/creative/ GeoStruct/anticline.jpg)







Joints are much like faults (cracks in the lithosphere) but do not occur on the border of moving plates or boundaries.  They are the result of the same stresses that are responsible for folding.  Jointing usually appears as a series of parallel lines.

(geoimages.berkeley.edu/.../Johnson/ Images/Large/CD2/095.jpg)








Last modified: September 05, 2004