The Physical Environment
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Tectonics and Landforms


When rocks deform by plastic deformation they can bend and fold. The process of folding occurs when rock is compressed, as it is along colliding plate boundaries. Upturned folds are called anticlines map icon and down turned folds are called synclines map icon. Anticlines and synclines are geologic structures, that is, they are folds in rock material. They give expression to the surface as linear ridges (anticlines) and troughs (synclines). The sides of the fold are called the limbs. Each fold has an axial plane, an imaginary plane that runs down its length and divides the fold in half. 

Figure 15.24 Components of a Fold


Symmetrical or open folds with their near-vertical axial planes and gently dipping limbs of about the same angle are a product of gentle compression. Symmetrical folds are found near the margins of mountain systems where tectonic activity is relatively quiet. If the compression is more pronounced from one direction, an overturned fold may occur. Extreme directed pressure may lay the fold over with its axial plane nearly horizontal with the surface producing a recumbent fold. Sometimes the length of the folds are tilted creating plunging folds. One of the best examples of folded topography is the Appalachian mountains found in the Ridge and Valley physiographic province of North America.



Figure 15.25 Teton Anticline, Utah
Photo credit: USGS Digital Data Series DDS-21


Figure 15.26 Syncline in Lockhart Basin, Utah
Photo credit: USGS Digital Data Series DDS-21


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For Citation: Ritter, Michael E. The Physical Environment: an Introduction to Physical Geography.
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Last revised 6/5/12

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