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Mountain Building An uplifting experience! How and where? • Deformation of crust from stress. – Compression = Rocks are squeezed together • Occurs at convergent boundaries – Tension = Crust is stretched apart • Occurs at divergent boundaries • Build-up of crust from volcanic activity. – Accretion (build-up of magma) inside crust stretches crust (tension) or erupts and accumulates on surface. – Occurs above subduction zones and “hot spots” FOLDING • Rocks bend without breaking • A response to compressional stress • Upward folds are called anticlines – These form mountain ranges • Downward folds are called synclines – These form valleys between ranges – http://www.wiley.com/college/strahler/0471480 533/animations/ch14_animations/animation2. html Faulting • Vertical Faults – Normal and Reverse – Defined by movement of “hanging wall” relative to the “foot wall”. • Horizontal – Strike-slip – Results from “shear stress” – Occur along transform boundaries Normal Faults • Form as a result of tensional stress – At divergent boundaries or above subduction zones. • Hanging wall slides down the foot wall. • The exposed footwall forms a cliff called a “fault scarp”. • • http://www.pbs.org/wnet/savageearth/animations/index.html http://www.classzone.com/books/earth_science/terc/content/visualizations/es1103/es1103page01.cfm?chapter_no=visualization Reverse Faults • Form as a result of compressional stress – At or near convergent plate boundaries • Hanging wall moves up relative to the foot wall. • If hanging wall gets pushed up and over the foot wall it is known as a “thrust fault”. • Often occurs along with folding. Fold Mountains • Form in collision zones from compression. • Form large systems with many ranges. • Examples: – Appalachian Mountains (past) – Alps (still forming) – Himalayas (still forming) – Rocky Mountains (past) Fault-Block Mountains • Usually form above subduction zones or continental hot spots. – Rising magma= tensional stress = normal faults. • Examples: – Teton Range (Wyoming) – Sierra-Nevada mountains (CA) – Exploring Earth Visualizations Tetons Volcanic Mountains • Form above active subduction zones or hot spots where magma erupts from the crust. • The erupted materials pile-up aroune the vent, forming a mountain. • Examples: – Some of the Cascade range (Oregon and Washington) – Some of the Andes mountains – Mountains of Japan, Phillipines, Indonesia