Chapter 9 NotesKey TermsMass wasting – a downslope movement of rock or soil as a more or less coherent massLandslides – the related phenomena of earthflows and mudflows, rock falls, and snow or debris avalanchesSubsidence – the very slow to rapid sinking or settling of Earth materialsSafety factor (SF)- the ratio of the resisting forces to the driving forces that cause landslidesRotational slides – when sliding occurs along a curved slip surfaceTranslational slides – occurs when movement takes place along a definite fracture planeSnow avalanche – the rapid downslope movement of snow and iceSinkholes – a circular area of subsidence caused by the collapse of a near-surface subterranean void or room in a cavernNotes- There are 5 types of slopes:Free face (cliff) Convex slopeStraight slopeTalus slope (rock fall deposits) Concave slopeVery hard strong granite Relatively weak rock- The stability of a slope depends on the relationship between the driving forces, which move Earth materials down a slope, and resisting forces, which oppose this movement- Driving and resisting forces on slopes are determined by the interrelationships of the following variables:o Type of Earth materials The weight of the slope material is the most common driving forceo Slope angle and topography Landslides are more frequent on steep slopeso Climate Affects the amount of water and vegetation that is presento Vegetation Amount of vegetation affects how much water can erode the slope Plant roots increase resistance to landsliding Vegetation adds weight to the slope, which can increase landslidingo Water Erodes the slope, which creates instabilityo Time The forces on slopes often change with time (ex. Seasonally, weathering, etc.)- The type of slope failure that occurs depends on what Earth materials the slope is made of o Failure commonly occurs on shale slopes, and slopes on weak volcanicpyroclastic materialso Slopes formed in resistant rock like sandstone, limestone, and granite do not experience the same problems- Types of human interactions that can cause landslides:o Timber Harvesting Logging on weak, unstable slopes greatly increases landslide erosiono Urbanization Hillside developments reduce many natural resisting forces- ex. Removing vegetation, cutting the bases of slopes, logging of lumber and fuel to make room for agriculture,increased water from sprinklers, etc.- Ways to minimize the landslide hazardo Identify Potential Landslides Examine geologic conditions Use aerial photographs to identify previous slideso Prevent Landslides by: Drainage Control Grading Slope Supportso Warning of Impending Landslides Surveillance, electrical systems, tilt meters, and geophones thatpick up vibrations from moving rockso Correcting Landslides Figure out what’s causing it and correct the problem- Ex. Excess water can be countered by implementing a draining program- Subsidence is caused either by the removal of fluids from ground reservoirs (i.e. oil & groundwater) or by the collapse of surface soil and rocks over subterranean