Mass Movement Overview and Types

Mass Movement Overview

• Mass movement is the downslope movement of soil and weathered rock due to gravity.
• Climate greatly influences weathering, determining the size and scale of mass movements.
• Almost all Earth's surface experiences some degree of mass movement.

Factors Influencing Mass Movements

• Material's weight: The weight of the material pulls it downslope.
• Material's resistance: This depends on friction, cohesiveness, and whether the material is anchored to bedrock.
• Triggers: Events like earthquakes shake materials loose, initiating movement.
• Water: Water increases the weight of materials and reduces friction between particles, facilitating movement.

Types of Mass Movements

Creep

• A slow, gradual downslope movement of loose, weathered soil.
• Effects are noticeable over long periods.
• Identifying features like tilted fence posts and trees can indicate creep.

Earthflows

• Moderately slow movement of soils.
• Mudflows are swiftly moving mixtures of mud and water.
• Often triggered by earthquakes or intense, short-lived rainstorms.
• Common in sloped, semi-arid regions and are especially destructive in urban areas near mountains.
• Lahars are mudflows in volcanic areas where melted snow carries volcanic sediment.

Landslides

• A rapid downslope movement of Earth materials.
• Landslides occur when a block of soil, rock, and debris separates from underlying bedrock, especially on steep slopes, often saturated with water.
• Slides: A sheet of rock moves downhill on a sliding surface. Often triggered by earthquakes.
• Slumps: Material moves along a curved surface. Common after heavy rain, acting like a lubricant between soil layers.

Avalanches

• Landslides involving snow, typically triggered when snow on an icy crust becomes heavy, slips off, and slides down a slope.

Rockfalls

• Rocks loosened by weathering (including plant growth) break and fall directly downward.
• Common in high elevations, steep road cuts, and rocky shorelines.