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Landslides: Slope stability, triggers, failure dynamics, and morphology - Types of landslides

Types of Landslides
            The mode of failure depends on the material type, the structure of the material (bedding, joints, and the orientation of these planes of weakness), and the slope. Different modes of failure can also combine in complex failures. Rocks tend to fail along pre-existing planes of weakness such as joints or bedding planes. Soils tend to fail in rotational slides along the radius of the sphere with the lowest factor of safety. They can also fail along planes of weakness, such as the interface between rock and soil. 

Rock Failures
            Rockfall
                        Occurs on steep slopes (greater than 40 degrees)
                        Individual boulders or disrupted rock masses
                        Most abundant failure during earthquakes
                        Often from slopes that were borderline stable under non-seismic conditions
                        Mostly in heavily jointed or weakly cemented rocks

            Rock slides
                        Failure along a pre-existing discontinuity
                        Similar material to rockfalls

            Rock Avalanches
                        Disintegrated landslide that can travel hundreds km per hour across low slopes
                        Typically occur when there is a large amount of kinetic energy in the slide                        
                        
(falling 
from a height)

            Rock Slumps
                        Similar to soil slumps (deep seated slides in very weak rocks)

Soil Failures
            Compared to rocks, soils are more isotropic, and do not commonly have dominant weak layers. Instead of failing along a pre-existing plane of weakness, soils often fail along a sub-spherical shell where the lowest factor of safety occurs.

            Soil falls
                        Similar to rockfall, but material involved is soil

            Disrupted soil slides
                        Disintegrate during movement
                        Most slide on basal shear surfaces at contact between bedrock and soil, some
                        slide 
on boundaries between different soil layers

            Soil Avalanches
                        Similar to disrupted soil slides, but faster moving and more disrupted

            Soil Slumps
                        Curved basal shear surface, deep seated

            Soil block slide
                        Movement along a planar surface, often deep seated

            Rapid soil flows
                        Streams of soil grains that flow in a fluid-like manner at high velocities

            Debris flows
                        Debris flows are a mixture of sediment and water. They are typically fast
                        moving 
and pose a serious hazard due to their speed, transport of large
                        
boulders, and variable viscosity. 

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