Note_-_Chapter_13 - Unsafe ground landslides and other mass movements Introduction Earth\u2019s surface is not terra firma it is mostly unstable Mass

Note_-_Chapter_13 - Unsafe ground landslides and other mass...

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Unsafe ground: landslides and other mass movements Introduction - Earth’s surface is not terra firma; it is mostly unstable - Mass movement (or mass wasting) is: - Downslope motion of rock, soil, sediment, snow and ice - Drive by gravity operating on anny sloping surface - Characterized by a wide range of rates (fast to slow) Mass movements - Mass movements are costly type of natural hazard - A crucial component of the rock cycle - May often cause damage to living things and buildings - These hazards can produce catastrophic losses - May 31, 1970: 18 000 people were buried in Yungay, Peru - Mass movements are important to the rock cycle - The initial step in sediment transportation - A significant agent of landscape change - All slopes are unstable; they change continuously - Mass movement is often aided by human activity Types of mass movement - Classification is based upon four factors: - The type of material (rock, regolith, snow, or ice) - The velocity of movement (fast, intermediate, or slow) - The nature of the mass (chaotic, coherent, or slurry) - The movement environment (subaerial or submarine) - Creep - slow downhill movement of regolith - Due to seasonal soil expansion and contraction - Wetting and drying - Freezing and thawing - Warming and cooling - Grains are moved: - Perpendicular to slope upon expansion - Vertically downward by gravity upon contraction - Creep is evident from tilting of landscape features - Trees - Telephone poles - Retaining walls - Foundations - Tombstones - Solifluction - low downhill movement of tundra - Melted permafrost slowly flows over deeper-frozen soil - This process generates hillsides with solifluction lobes
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- Slumping - sliding of regolith as coherent blocks - Slippage occurs along a spoon-shaped “failure surface” -
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