Slope Processes & Mass Movement

What is a slope?

A slope is any inclined surface, such as a hill slope, defined by its slope angle.

What are the causes of slope failure?

Slope failure can be caused by increased shear stress or decreased shear strength.

What causes increased shear stress in slope failure?

Increased shear stress can occur due to the removal of lateral support, undercutting, slope steepening, slope loading, lateral pressure, or transient stresses.

What causes decreased shear strength in slope failure?

Decreased shear strength can result from weathering effects, changes in pore-water pressure, changes in structure, or organic effects.

What opposes mass movement on slopes?

Friction, cohesive forces, pivoting, and vegetation oppose mass movement.

What is soil creep?

Soil creep is the slow movement of soil particles caused by wetting, heating, and freezing of water, mainly occurring in winter.

How do soil particles move during soil creep?

Soil particles are heaved to the surface and then fall under gravity once they dry, cool, or thaw, resulting in net movement down the slope.

What evidence indicates soil creep?

Evidence includes tension cracks in roads, tilted poles, terracettes, and soil piled behind field stone walls.

What is talus creep?

Talus creep is the slow movement of fragments along a scree slope.

What are slumps in mass movement?

Slumps are movements where weaker rocks like clays slide with a rotational movement along a curved slip plane.

What happens during a slump?

Clay saturates and flows along the slip plane, often occurring when the base is undercut. Slumps produce separate, jerky events.

What are flows in mass movement?

Flows are a continuous, smoother form of slump that occur in deeply weathered clay when particle size is the same or smaller than sand grains.

What is the difference between mudflows and earthflows?

Mudflows are faster than earthflows and occur on shallower slopes due to higher water content.

Where can flows occur?

Flows can occur on the saturated toe of a landslide or as separate events.

What are falls in mass movement?

Falls occur on steep slopes (>40°) with bare rock faces and exposed joints, where rocks detach and fall freely under gravity.

What type of scree is produced in rock falls?

If the fall is short, a straight scree is produced; if it is longer, a concave scree is produced.

How do falls contribute to slope dynamics?

Falls contribute to the retreat of steep rock faces and provide debris for scree or talus slopes.

What are slides in mass movement?

Slides occur when a mass of material moves along a slip plane, and the material holds its shape until hitting the slope bottom.

What conditions cause slides?

Slides occur in weak rocks, on steep slopes, with active undercutting, intense cold, or sudden changes in water content.

What are landslides?

Landslides occur when material moves downslope due to shear failure, where downward force exceeds resistance.

How does water content affect landslides?

An increase in water content reduces the strength of materials by pushing particles apart, contributing to landslides.

What are rockslides?

Rockslides involve a large rock mass sliding down a slip plane.

What is a slip plane?

A slip plane is the junction between two layers along a bedding line or the joint between two rock types, where shear stress exceeds shear strength.