Overview
This lecture introduces landslides and mass movements, explaining their importance, types, causes, hazards, and impacts on landscapes and human communities.
Introduction to Mass Movements
- Slopes are common in physical landscapes and vary in steepness and composition.
- Mass movement (mass wasting) is the downslope movement of rock, regolith, and soil under gravity.
- Mass movements occur at various speeds and scales, from gradual soil creep to catastrophic landslides.
Types and Impacts of Landslides
- "Landslide" refers to rapid downslope movement of rock or soil as a coherent mass.
- Landslides become hazards when they threaten people, property, or infrastructure.
- Mass movements follow weathering, helping to form features such as valleys.
- Most mass movements occur in rugged, geologically young mountains, gradually transforming them into gentler terrain.
- Landslides can happen almost anywhere, including underwater, and are not limited to steep slopes.
Hazards and Examples
- Hundreds of deaths and substantial property damage occur annually from landslides worldwide.
- Deadliest recorded landslide: 1920, China, triggered by an earthquake, causing over 100,000 fatalities.
- Notable recent examples include landslides in Norway (2020), California (2018), Guatemala (2015), Japan (2016), and Alaska (2016).
The Vaiont Dam Disaster
- Vaiont Dam (Italy) failed in 1963 due to landslide triggered by heavy rain and rising water table, displacing 700,000 cubic meters of material in 10 minutes.
- The landslide created a massive flood, killing over 2,000 people despite the dam itself remaining intact.
Factors Influencing Landslides
- Geology (e.g., weak rocks such as shale or easily dissolved limestone) and topography contribute to landslide risk.
- Human activity often increases the frequency and intensity of mass movements.
- Gravity is the ultimate controlling force behind all mass movements.
Key Terms & Definitions
- Mass Movement (Mass Wasting) — Downslope movement of rock, regolith, or soil due to gravity.
- Landslide — Rapid downslope mass movement of rock or soil as a relatively coherent mass.
- Regolith — Layer of loose, heterogeneous material covering solid rock.
- Weathering — Breakdown of rocks at Earth's surface, providing material for mass movement.
Action Items / Next Steps
- Prepare for quiz/activity questions about gravity’s role in mass movement.
- Watch the next video to learn about the different types of mass movements.