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Faulting
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What is Faulting?
● Weakness in the earth's crust caused by earth
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movements
Leads to fractures in the earth's crust
Convection currents in mantle
Faults force land up, down or sideways
Down - normal fault (pulling apart)
Up - reverse fault (pushing together)
Sideways - Transform fault (sideways)
Rock may slip very little each time (1-5 cm per year)
In geological time (slippage = 100s of kilometres)
Normal Fault
● Tension (Pulling Apart)
● Crust falls relative to
other sections of crust
● Slope is known as a
"scarp"
● The section that falls is
known as a rift valley
● East African Rift Valley
○ many deep lakes due
to faulting
○ New plate will form in
millions of years
East African Rift Valley
African Plate
Fault Line
Somalian Plate (will break
away from African plate in
millions of years)
Normal Fault
Block Mountain
Fault Scarp
Rift Valley
Normal Fault
Normal Faults can lead to block mountains
● where a section of crust slips down and
leaves a middle section above the two sides
● Looks likes a plateau or mountain with
straight sides
● Example - Ben Bulben, Co. Sligo
Normal faults
& block mountains
Block Mt
Rift Valley
Ben Bulben
(Block Mountain)
Reverse Fault
● Compression caused by earth movements
● also known as thrust faults
○ section of crust is pushed over another section
○ one section of crust is buried
● can occur together with normal faults
● lead to fold mountains, e.g. Armorican fold
mountains in Munster (Caha & Galtee
Mountains)
● Sandstone pushed over limestone
Reverse Fault
Diagram
Galtee Mountains
Transform / Transverse
Diagram
San Andreas Fault
San Andreas Fault
● Pacific Plate moving
northwest
● American Plate moving
south
● Movement is about 5 cm
per year
● Lateral motion
(sideways) and not up or
down
● May lead to earthquakes