Physical Geography: Folding And Faulting
How folding occurs
Two continental plates collide
Compression
Fold mountains created with anticlines, synclines and limbs
There are four types of fold:
Simple fold
Asymmetrical fold
Overfold
Overthrust fold
Fold mountains
Caledonian orogeny
400 MYA
Example: Wicklow Mountains
American and Eurasian plates collided
SW–NE trend
Oldest mountains, low
Fault lines
Armorican orogeny
250 MYA
Example: ridge and valley landscape of Munster (Case Study)
African and Eurasian plates collided
Folding E–W trend
Old red sandstone, 380 MYA Ireland was a hot desert
350 MYA limestone developed on top
Two plates collided, rock strata folded into anticlines and synclines
Softer rocks, e.g. chalk removed by denudation
Limestone remained in synclines
Trellised drainage pattern developed
Rivers Bandon, Lee, Blackwater
Alpine orogeny
30 MYA
Example: the Alps, did not affect Ireland
African and Indian plates collided with the Eurasian plates
Highest and youngest peaks
Faulting
A moving fracture or break in the Earth’s surface created by pressure or tension
Normal Fault
Example: Clew Bay, Co. Mayo
One side of the fault slips down
Tension, creates a scarp
Two faults parallel: land slips down, rift valley; land compressed upwards, block mountain
Reverse Fault
Example: Pollatomish, Co. Mayo
Land compressed
Block mountains
Thrust fault, less than 45 degrees
Tear/transform fault
Example: San Andreas Fault, California
Vertical fault
Horizontal plate movement
Doming
Found in sedimentary rocks
Upturned bowl
Molten magma pushes to surface, bulges
Overlying rock layers removed by denudation
Example: Slieve Bloom Mountains, Co. Laois
Case Study: Landform of faulting – African Rift Valley
Parallel fault lines 4,800 km
20 MYA
Tension due to rising magma
Scarps formed
Between 40 and 100 km wide
If continues, eastern part of Africa will split apart