Draw diagrams explaining the formation of a rift valley and a block mountain. Remember, all diagrams must have a title and a frame, and be fully labelled.
Block mountain
Also known as a horst, a block mountain is formed when compression creates two parallel faults and the large block of land in-between is pushed upwards, forming a hill or mountain (Fig. 4.11). The upthrown block is the horst. Block mountains in Ireland include the Ox Mountains in County Sligo.
Parallel faults A-Z
Slip fault: Another term for a tear fault.
EXAM LINK (HL)
Landform Development (30 marks)
Explain how one of the following influences the development of landforms: Folding / Faulting.
2015, Q3B Marking Scheme:
Landform identified = 2 marks
Examination = 14 SRPs × 2 marks
Block mountain: compression force – central block of crust is uplifted
Fig. 4.11 Block mountain. Faults resulting from shearing
Tear fault A tear fault is caused by lateral movement at transform plate boundaries. While crust is neither created nor destroyed, rocks at the edge of both plates can lock in position. Stress builds up at the boundary as convection currents continue pushing the plates laterally past each other. Earthquakes are generated when rocks at the boundary eventually break, allowing the plates to move forward very suddenly (Fig. 4.12(a)).
Along the San Andreas Fault line, the Pacific and North American plates are both moving north-west but at different speeds (Fig. 4.12(b)). Earthquakes occurring here are particularly violent, as the focus of the earthquake tends to be close to the surface of the earth’s crust.
Tear fault: shear force – crust is horizontally displaced
Fig. 4.12(a) Tear fault. 52 Fig. 4.12(b) The San Andreas fault.
