Mass movements Falls, slumps flows Landslide scar/scarp

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Presentation transcript:

Mass movements Falls, slumps flows Landslide scar/scarp Slump/slip plane Rupture surface (may be curved for rotational slump) Earthflow/mudflow Toe of landslide Slump block

Classification of mass movements

PHYSICAL FACTORS AFFECTING AND CAUSING LANDSLIDE HAZARDS Geological structures such as faults, joints and bedding planes are potential planes of weakness High permeability and porosity of rock and regolith allow greater water content Earthquakes may act as a trigger factor Heavy rainfall saturates soils and rock increasing the weight of the deposits and increasing the effect of gravity Snow/ice melt increases water content Volcanic activity may melt ice and snow to give a lahar Steeper slopes increase the effect of gravity Previous/antecedent rainfall may leave deposits already saturated Erosion and undercutting of the base of the slope by a river or the sea weakens the slope Weathering breaks and loosens the rocks reducing internal cohesion. Unconsolidated, incompetent rocks fail more easily Increased water content increases the shear stress within the sediments Water content reduces shear resistance of sediments and acts as a lubricant between particles Freeze thaw processes open up the pores and cracks in the sediments producing minimum density packing and allowing greater water content The destruction of vegetation by fire/drought weakens the sediments and causes water content to increase

HUMAN FACTORS AFFECTING AND CAUSING LANDSLIDE HAZARDS Overgrazing and other poor agricultural practices that reduce vegetation cover also weaken coherence of the sediment Developments or waste tipping may add weight/load to the top of the slope Deforestation reduces interception and transpiration increasing infiltration and overland flow Developments may cause water or sewage leakages that increase water content Mining and excavations may steepen slopes and cause blasting The slope may be undercut and slopes steepened by developments such as road construction Vibrations caused by blasting and heavy traffic can be a trigger factor Dams and reservoirs may add weight to sediments or leakage may weaken sediments leading to slope failure