How the Crust is Deformed Deformation- the bending, tilting,
and breaking of the earths crust Major cause- plate tectonics Plate
movement is not the only thing that shapes the earths crust
Slide 3
Isostatic Adjustment Some changes in the earths 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
Slide 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
Slide 5
Stress Isostatic adjustments and plate movement cause stress in
rocks that make up the earths 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
Slide 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
Slide 7
3 types of Stress Tension- force that pulls rocks apart Rocks
tend to become thinner
Slide 8
3 types of Stress Shearing- pushes rock in opposite horizontal
directions Rocks bend, twist, or break apart as they slide past
each other
Slide 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
Slide 10
The Results of Stress Faulting Cooler temperatures and lower
pressure near the earths 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
Slide 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
Slide 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
Slide 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.
Slide 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
Slide 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
Slide 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
Slide 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
Slide 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
Slide 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
Slide 20
Plate Tectonics & Mountains Collisions Between Continents
Two continents collide Ex: Himalayas
Slide 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
Slide 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
Slide 23
Fault-Block Mountains and Grabens Fault-Block Mountains Formed
where parts of the earths 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
Slide 24
Volcanic Mountains Mountains that form when molten rock erupts
onto the earths 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
Slide 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
Slide 26
http://youtu.be/zPfILoG7ojo http://youtu.be/uoyrqhUbiko
Formation of the Rocky Mountains