Folding and Faulting

recumbent fold
overthrust fault
The compressional force exerted on the crust is a
result of movement of earth’s plates.
When the plates converge, the weak rocks and
sediments lying between the 2 plates get squeezed
and get folded.
Parallel folds give rise to long chains of parallel
mountain ranges with high peaks.
The up-folds form fold mountains while the down
folds form longitudinal valleys.
The Valley of Ten Peaks, Banff National Park
Faults are large scale internal
movements causing large scale
physical features especially
mountains and valleys
If the force is moderate only
cracks may appear in the rocks.
The displacement that occurs
results in formation of faults.
Such fractures are divided into
Joints & Faults.
A joint is a fracture where a rock
seems to be joined together
without any movement
it may become a fault when
displacement takes place
Normal faults occur when tensional forces act in opposite directions and
cause one slab of the rock to be displaced up and the other slab down
Reverse faults develop when compressional forces exist
Compression causes one block to be pushed up and over the other block.
A graben fault is produced when tensional stresses result in
the subsidence of a block of rock. On a large scale these features are
known as Rift Valleys
Major relief feature of Faulting Activity is Rift Valley.
A Rift Valley may be formed in two ways :
(1) When the middle portion between two normal faults is dropped
downward the sides remain stable.
(2) When the middle portion remains stable and the two sides are
raised upward
These valleys have flat bottoms and steep sides
The Ottawa-Bonnechere Graben (also known as the Ottawa
Graben), with its branch the Timiskaming Graben, is an
ancient rift valley in the Canadian Shield of Northeastern
Ontario and Quebec, Canada
This rift valley was formed when the Earth's crust moved
downward about a kilometre between two major fault
zones known as the Mattawa and Petawawa faults
These ancient faults are still active and occasionally release
stress in the form of earthquakes, such as the 1935
Timiskaming earthquake and the 2000 Kipawa earthquake.
The length of the graben is about 700 km (435 mi)
Runs from the Montreal area on the east to near Sudbury and
Lake Nipissing on the west
A horst fault is the development of two reverse faults causing a block of
rock to be pushed up
- In German Horst = 'heap'
Block mountains are another
important feature of Faulting caused
by the Tensional features in the
Earth’s crust
The mechanism of formation of
Block mountains is same as the Rift
The Block mountains are often
found on the sides of the Rift valley
It is because the land between two
parallel faults is either subsides to
form a Rift valley or rises to form
Block mountains
transform fault

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