Outcomes: Explain how tensional forces create a normal fault.
Explain how compressional forces create reverse and overthrust faults.
Tectonic Faults
Fault lines are great cracks in the crust. There are a number of types of mountains created by faults or
“faulted mountains”.
Mountains Formed by Normal Faults
Normal Faults are caused by tensional forces. When the land moves apart at a fault line one plate drops
down lower that the other.
In normal fault tensional forces cause the tectonic plate referred to as the “hanging wall” to fall.
Mountains Formed by Reverse Faults
Reverse faults are caused by compressional forces where plates move together at the fault. The land
that rises above can form a mountain.
Fault Block Mountains
Fault Block Mountains sometimes form when many layers of the Earth's crust are moved vertically
upward between two parallel fault lines. Vertical force is caused by the earth's internal pressure. The
mountains that are formed in this way are called fault-block mountains. The Sierra Nevada mountains in
California and Nevada, and the Grand Teton range of Wyoming are examples of fault-block mountains.
Sometime the magma in the asthenosphere moves in such a way to create an upward current strong
enough to cause a section of a tectonic plate to break free and move upwards.
Overthrust Faults
Overthrust Faults are caused by compressional forces where plates move together at the fault. They are
a class of reverse faults that have had folding occur before the faultformed.