1	Mass Wasting
2	Definitions Mass movement: Downslope movement of material under the action of gravity (Landslide in our everyday parlance) Mass wasting: All the processes by which mass movement takes place >$1 billion damage every year in US 25-50 deaths in US
3	Factors Nature of slope material (unconsolidated or consolidated?) Water content Steepness of slope Vegetation
4	Nature of slope material Gentler slopes have less mass wasting and steeper slopes have more mass wasting Massive rocks form stable slopes, weaker rocks, fractured rocks or jointed rocks are more prone to failure Angle of repose = maximum angle at which loose material will stand without sliding. Dry Sand: angle of repose = 35°
5	Slope modification for road building
6	Effect of Water
7	Triggers Earthquakes: Northridge Earthquake 1994: Major storms can saturate the ground: Hurricane Mitch Undercutting: River or coastal erosion undercuts slopes, producing steep cliffs that are susceptible to mass wasting. Volcanoes, especially stratovolcanoes: example: Huascarán debris avalanche triggered by a 7.7 earthquake offshore: , Mt. St. Helens, Mt. Pinatubo, Philippines Erupted June 12, 1991, many mudflows since then Steepening slope (Often by humans) Decrease, increase vegetation (logging, forest fire) Adding weight to slope (irrigation, sewers, lawn watering)
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10	Classification How is it moving? Fall: chaotic, free falling, rapid (m/sec) slide (slump) coherent mass, in contact with the underlying surface, (m/yr to m/sec) slump - moves along a curved concave-upwards surface, associated with a scarp at the head flow(creep, flow and avalanche) continuous fluid-like movement where different parts of the flow move faster or slower. Their speed depends on varying proportion of sediment and water or air. What is moving? Rock, debris (mixture of rock, soil, trees …) and soil(mud, earth)
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12	Classification of Mass Movements
13	Rock Fall
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22	Characteristics Mudflow - higher speed and more water than debris flow Debris flow - higher speed and more water than Earth flow (moves like wet concrete), Debris avalanche - very fast average > 100 mi/hr mixed with air, up to 600? mi/hr Huascarán, Peru 1970 - debris avalanche triggered by 7.7 magnitude earthquake. Speed estimated: 400km/hr (240 mi/hr) to 1000km/hr (600 mi/hr). Two towns buried - Yungay and Ranrahirca, >18,000 died.
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24	Creep and Solifluction Creep - very slow - < 1 foot/yr, little water -- signs of creep - tilted poles, bent tree trunks (pistol butt) - destructive to property Solifluction: Occurs in very cold climate where the ground is frozen year round (Permafrost). During the Spring thaw, melt water from the shallow depths cannot percolate deeper in the ground. This water saturates the soil which then flows
25	Creep
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28	Minimizing Landslide hazards Identifying potential landslides Use of maps and aerial photograph to identify past and present slides Slope map Warning Systems Human Geophones, tilt meter, electrical systems, monitoring of rainfall
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30	Prevention Drainage Control and Fluid Removal Slope reduction Retention structure Vegetation Fence Rock-bolt (for thinly bedded strata prone to rock slide) Shelters
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36	Retention Wall
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