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EOSC114 - Landslides 3.docx

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Earth and Ocean Sciences
EOSC 114
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EOSC114 - Landslides 3 EXTERNAL CAUSES High slope angle Must have a slope for mass movement Steeper= more movement Undercutting Lower part of slope is removed Removes material supporting the slope Ex. Caused by road, rivers, buildings, etc. Overloading Adding weight (to top of slope, or somewhere on slope) Ex. Caused by buildings, roads, landslides, trees, etc. Vegetation Good factors of it… Roots bind loose material Not so good factors of it… Removal of vegetation can make slopes unstable Heavy trees can increase instability (overloading) Climate If average temperature and rainfall is high more water increased weathering of rocks more fractures more soil If average temperature is around 0 (SEE INTERNAL CAUSES) INTERNAL CAUSES WATER CONTENT Adds weight (overloading) Decreases normal force/normal stress, which decreases friction and thus  with little f Does not lubricate Increases weathering Acts as a medium for flows In sediment: (loose rocks, sand, silt, and clay) Water can help OR hinder cohesion Depends on the amount of water Sediment No water = low angle of repose Some water = high angle of repose Too much water = very low angle (oversaturated) Solid rock Water reduces shear strength along planes of weakness (fractures) Or causes… Frost wedging Colder climates Water gets into cracks and fractures in rock If it freezes it expands – forcing the fractures apart If facing sun can melt – more cycles INHERENTLY WEAK MATERIALS Some materials are very weak Fail at relatively and/or very low angles of repose Ex. Volcanic rock or “quick clay” Volcanic layers are weak along planes of weakness w/wat
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