• Normal fault: Divergent plate boundary – tension – earth’s crust stretches, become thinner and eventually fractures – one block of land displaced – moves downwards
• Graben fault: Tension – two parallel faults – large block of land in-between slips downwards – forms rift valley with steep escarpments – Death Valley in California and the Rhine Rift Valley in Germany
Faults resulting from compression
• Reverse fault: Convergent plate boundary – compression – earth’s crust fractures – one block of land moves upwards.
• Thrust fault: Type of reverse fault – plane is inclined – angle equal to or less than 45°
• Block mountain (horst): Compression – two parallel faults – block of land in-between pushed up forming a hill or mountain – Ox Mountains in Co. Sligo
East African Rift Valley • Created by faulting in the last 20 million years – stretches for over 4,800 km from Syria to the Zambezi River
• Convection currents – two normal faults created by tension – centre portion of land slipped – formed a flat-floored rift valley
• Rift valley lies more than 153 m below sea level in places • Volcanoes (Mount Kilimanjaro) and lakes (Tanganyika) have formed on the floor of the rift valley • Rift valley is widening by 4 mm per year – continent of Africa will eventually split apart if the rifting process continues
Faults resulting from shearing
• Tear fault: Lateral movement – transform plate boundary – San Andreas Fault in California – Pacific and North American plates moving horizontally – no land created or destroyed but earthquakes common – violent, as focus tends to be close to the surface of the earth’s crust
