Roles of Slope and Friction. Role of Earthquakes - shake the ground where things are metastable and they all come tumbling down. Viaont Dam Disaster, Italy, 1963. Boulders in a field tend to weather from beneath. Compressibility - tendency to consolidate, compress.
Sand is low, clayey soils are High.
Erodibility - tendency to erode by wind and water. Permeability - ease of flowing water through. Soils erode, leaving hardened ground, lessening infiltration further. Four wheeling can be very bad for certain areas. Runoff as much as 8 times faster than adjacent areas, sediment yield comparable to that of construction sites.