Landslides and Mass Movements Explained — Types, Triggers, and Slope Hazard Mitigation | Chapter 16 from Earth: Portrait of a Planet

Landslides and Mass Movements Explained — Types, Triggers, and Slope Hazard Mitigation | Chapter 16 from Earth: Portrait of a Planet

Why do slopes collapse, and how can we prevent disasters? Chapter 16 of Earth: Portrait of a Planet by Stephen Marshak explores the science and hazards of landslides and mass movements—natural processes that reshape landscapes and threaten communities. For a podcast summary, watch the chapter video on YouTube, or read below for a comprehensive breakdown.

Book cover

What is Mass Movement?

Mass movement (or mass wasting) refers to the downslope transport of rock, soil, snow, or ice under gravity. These events range from slow soil creep to rapid, catastrophic landslides and avalanches, impacting both natural landscapes and human infrastructure.

Types of Landslides and Mass Movements

  • Creep: Gradual, imperceptible downslope movement of soil and regolith.
  • Solifluction: Slow, water-saturated soil flow, often in cold climates.
  • Slumps: Rotational movement along a curved surface.
  • Debris Flows and Mudflows: Rapid movement of water-charged soil and rock; lahars involve volcanic debris.
  • Rockfalls: Free-fall of rock from cliffs.
  • Avalanches: Sudden movement of snow or debris, triggered by overloading, melting, or vibration.
  • Submarine Mass Movements: Underwater slumps and turbidity currents, which can generate tsunamis.

Slope Stability and Failure Triggers

Whether a slope remains stable or fails depends on the balance between resistance force (friction and cohesion) and downslope gravitational pull. The angle of repose is the steepest angle at which a pile of loose material remains stable.

Common triggers for slope failure include:

  • Earthquakes and ground vibration
  • Heavy rainfall or rapid snowmelt (saturation)
  • Undercutting by rivers, waves, or construction
  • Deforestation and vegetation loss
  • Substrate weakening by weathering or human activity
  • Liquefaction and quick clay hazards

Notable Case Studies and Disasters

  • 1970 Yungay landslide (Peru)
  • Vaiont Dam rockslide (Italy)
  • 2014 Oso mudslide (Washington, USA)
  • Storegga Slide (Norway) — Submarine landslide and tsunami

These disasters highlight the deadly potential and complexity of mass-movement hazards worldwide.

Monitoring, Mapping, and Mitigation Strategies

  • Monitoring: Satellite tiltmeters, ground sensors, and landslide-potential maps help predict failures.
  • Prevention: Slope regrading, drainage improvements, revegetation, rock bolts, retaining walls, avalanche sheds, and riprap all increase slope stability and reduce risk.
  • Hazard Zoning: Identifying and restricting development in high-risk areas, especially in tectonically active zones.

Conclusion: Living with Slope Hazards

Landslides and mass movements are natural, but their impacts can be minimized through scientific understanding, engineering, and careful land use. As climate change and population growth increase risk, ongoing monitoring and mitigation become ever more vital.

For a detailed visual summary, watch the full chapter video on YouTube. And don’t forget to subscribe to Last Minute Lecture for more textbook chapter breakdowns and hazard guides.

Continue learning with the Earth: Portrait of a Planet complete chapter playlist.

If you found this breakdown helpful, be sure to subscribe to Last Minute Lecture for more chapter-by-chapter textbook summaries and academic study guides.

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