Name:______________________________________
Block:________
Mountain Building and Faults (Revised)
Where Mountains Form
o Most of the world’s mountains occur in long belts that tend to
follow convergent plate boundaries.
o Continental margin- boundary between continental crust and
Active continental
margin
oceanic crust.
o Active Margins have volcanoes – at plate boundaries
Passive Margins – no volcanoes – not at boundaries
Passive continental
margin
How Mountains Form
o Mountains form because stress is applied to rocks at converging plate boundaries. Stress is a measure of
force applied over a given area.
o Types of stress:
o Compression- rock layers are squeezed inward
o Tension- rock layers are being stretched
o Shear- rock layers are being pushed in two different,
opposite directions.
o Folds
o During plate collisions, stress can cause rock layers along continental margins to crumple into
folds.
o Anticline- upfold in the rock layer
Oldest rocks at center
o Syncline- downfold in the rock layer
Youngest rocks at center
o The Valley and Ridge province is a wellknown example of folds.
o Faults
o A fault is a break in the lithosphere along which movement has occurred.
o Normal fault- hanging wall moves down with respect to the footwall, tension stress
o Reverse fault- hanging wall moves up with respect to the footwall, compression stress
o Thrust fault- reverse fault in which the fault plane dips 45 or less from the horizontal.
o Strike-slip fault- rocks on opposite sides of the fault plane move horizontally. The San Andreas
is a well-known strike-slip fault.
o
o Horsts and Grabens- occurs from tensional stress
and normal faulting.
Types of Mountains
o Folded Mountains-Two plates carrying continental crust collide. Ex: Appalachians and Himalayas
o Dome Mountains- individual, isolated structures that occur in flat lying rock. A nearly circular folded
mountain.
o Volcanic Mountains- Occurs when there is a collision between an oceanic plate and continental plate
and subduction occurs. The volcanic mountains form on the continental plate.
o Fault-Block Mountains- In areas where the crust is uplifted it forms normal faults. The tension and
uplift causes whole blocks of crust to be pushed up.