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
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
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.
Formation of the Rocky Mountains