Deformation of Crust

1. Deformation of Crust Fall 2013

2. How the Crust is Deformed • Deformation- the bending, tilting, and breaking of the earth’s crust • Major cause- plate tectonics • Plate movement is not the only thing that shapes the earth’s crust

3. Isostatic Adjustment • Some changes in the earth’s crust occur because of changes in the weight of some part of the crust • When parts of the crust become thicker and heavier, they sink more deeply into the mantle • When parts of the crust become thinner and lighter, they rise higher on the mantle

4. Isostatic Adjustment • The up & down movements of the crust occur because of two opposing forces • The crust presses down on the mantle • Mantle presses up on the crust • Isostacy- balance of these two forces • Up & down movements of the crust to reach isostacy are called isostatic adjustments • As isostatic adjustments occur, areas of the crust are bent up and down, pressure created by this causes the rocks in that area of the crust to deform • Constantly occurs in areas of the crust with mountains • Can also be found in areas where there are large bodies of water or where glaciers once were

5. Stress • Isostatic adjustments and plate movement cause stress in rocks that make up the earth’s surface • Stress- amount of force per unit area that is placed on a given material • Crustal stress occurs when lithospheric plates collide, separate, or rub together • Causes strain in crust rocks • Strain is a change in the shape or volume of rocks that results from the stress of being squeezed, twisted, or pulled apart

6. 3 Types Of Stress • Compression- occurs when crustal rocks are squeezed together • Often reduces the volume of rocks • Tends to push the rocks up higher or deeper down into the crust

7. 3 types of Stress • Tension- force that pulls rocks apart • Rocks tend to become thinner

8. 3 types of Stress • Shearing- pushes rock in opposite horizontal directions • Rocks bend, twist, or break apart as they slide past each other

9. The Results of Stress • High pressures and temperatures caused by stress in the crust generally deform rocks. • If the force exceeds a certain limit, the shape of the rock changes permanently

10. The Results of Stress • Faulting • Cooler temperatures and lower pressure near the earth’s surface often cause rock to respond to stress by breaking • 2 categories of breaks in rocks • Fracture- when there is no movement in the rock along either side of the break • Faults- when there is movement in the rock along either side of the break

11. The Results of Stress • Faulting cont… • Fault plane- surface of the fault along which any motion occurs • Hanging wall- rock above the fault plane • Foot wall- rock below the fault plane

12. Types of Faults • Normal fault • Fault in which the hanging wall moves down relative to the footwall • Form along divergent boundaries • Usually occur in a series of fault lines, forming step-like land forms • Ex: Great Rift Valley

13. Types of Faults • Reverse fault • Forms when compression causes the hanging wall to move up relative to the footwall • Thrust fault- special type of reverse fault in which the fault plane is at a low angle or nearly horizontal • The rocks in the hanging wall are pushed up and over the rocks in the footwall because of the low angle of the fault plane.

14. Types of Faults • Strike-slip fault • Rock on either side of the fault plane slides horizontally • Often occur at transform boundaries • Ex: San Andreas Fault Faulting

15. Mountain Formation • Mountain range- a group of adjacent mountains with the same general shape and structure • Ex: Mount Everest is in the Himalaya Range • Ex: Mount St. Helens is in the Cascade Range • Mountain system- a group of adjacent mountain ranges • Ex: Great Smoky, Blue Ridge, Cumberland, & Green mountain ranges all make up the Appalachian mountain system

16. Mountain Formation • Mountain belt- group of large mountain systems • 2 major belts on earth • 1) circum-Pacific belt- forms a ring around the Pacific Ocean • 2) Eurasian-Melanesian- runs from the Pacific islands through Asia and southern Europe and into northwestern Africa

17. Plate Tectonics and Mountains • Both the circum- Pacific and Eurasian-Melanesian mountain belts are located along convergent plate boundaries • Leads scientists to believe that most mountains were formed when lithospheric plates collided

18. Plate Tectonics & Mountains • Collisions Between Continental & Oceanic Crust • Oceanic crust is subducted beneath the continental crust • Subduction of the oceanic crust causes partial melting of the overlying mantle material, producing magma that may eventually erupt & form volcanic mountains

19. Plate Tectonics and Mountains • Collisions Between Oceanic Crust and Oceanic Crust • Volcanic mountains sometimes form where two plates with oceanic crust at their edges collide • One plate subducts beneath the other, water from the subducting plate induces partial melting of mantle material to form magma • Magma rises and breaks through the ocean crust • Forms an arc of volcanic mountains on the ocean floor • Ex: Mariana islands

20. Plate Tectonics & Mountains • Collisions Between Continents • Two continents collide • Ex: Himalayas

21. Types of Mountains • Scientists classify mountains according to the way in which the crust was deformed and shaped by mountain-building forces. • Types of Mountains: • Folded Mountains & Plateaus • Fault-block Mountains & Grabens • Volcanic Mountains • Dome Mountains

22. Folded Mountains and Plateaus • Folded Mountains • Highest mountain ranges in the world • Commonly found where continents have collided • Tectonic movements have squeezed rock layers together like an accordion • Plateaus • Large flat topped rocks high above sea level • Formed when thick, horizontal layers of rock are slowly uplifted • Most are found next to mountain ranges • Ex: Tibetan Plateau is next to the Rockies

23. Fault-Block Mountains and Grabens • Fault-Block Mountains • Formed where parts of the earth’s crust have been extended and broken into large blocks & faulting tilted the blocks and caused some blocks to drop down relative to other blocks • Ex: Sierra Nevada range • Grabens • Develop when steep faults break the crust into blocks and a block slips downward • Ex: Death Valley

24. Volcanic Mountains • Mountains that form when molten rock erupts onto the earth’s surface • May develop on land or on the ocean floor • Ex: Cascade Range • Some of the largest volcanic mountains are found along divergent plate boundaries, which form the mid-ocean ridges • Ex: Hawaiian Islands- tips of high volcanic mountains that formed over a hot spot on the sea floor

25. Dome Mountains • Unusual type of mountain • Formed when molten rock rises through the crust and pushes up the rock layers above it • Ex: Black Hills in South Dakota

26. http://youtu.be/zPfILoG7ojo • http://youtu.be/uoyrqhUbiko • Formation of the Rocky Mountains