1. Intro

• Includes all processes that involve the movement of rock and/or soil downslope.
• Important erosional and transport mechanism particularly in tectonically active, mountainous areas and near steep shorelines.
• Important as a significant engineering problem and human hazard

• Balance between driving forces (gravity) and resisting forces (friction).
• Driving force- the downslope component of weight (gravity driven). F_d = wsinq         (downslope force = weight times the sine of the slope angle).
• Resisting force- related to the shear strength of the slope material and the length (l) of a potential slip surface.
• Factors affecting slope stability
• Slope and topography- increase q will increase Fd.
• Amount of water in the materials
• surface tension increases shear strength if material is undersaturated.
• decreases shear strength if material is saturated.
• Related to climate and vegetation conditions.
• Nature of the material and geological factors
• variation in shear strength of rocks and soils.
• local bedrock structure (ie. sloping layers)

• Undercutting of the base of a slope (natural erosion or by humans).
• Loading of the upper part of the slope (usually human)
• Vibration due to earthquake
• Increase in moisture content (rainstorm or irrigation)
• Change in vegetation or climate

• nature of material (rock or unconsolidated)
• nature of the movement (flowing, sliding, falling)
• speed of movement (slow or fast)

• Creep- very slow (cm/yr) of unconsolidated material.
• Flow - unconsolidated material that mixes during movement
(earthflow, debris flows, mudflows, debris and rock avalanches)
• Sliding- movement of a coherent mass of soil or rock.
(slumps, debris slides, rocks slides)
• Falling- materials free fall through the air (rock falls)