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Mass Movement Hazards
Hazards, Vulnerability and Resilience (GEO5100-20)
Bath Spa University
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Mass Movement Hazards
Slopes and the range of mass movement types
What are slopes? Past geomorphological study of hillslopes 1950s - form 1960/70s - process Recent - integrated/predictive material , processes and form interconnection
2 key types of material - rock and soil (regolith) Response of material to stress is determined by its strength. Pre-failure get deformation (strain) Shear Strength - Variability, angle of internal friction Gravity - normal and shear stress Threshold angle of stability is the maximum angle when failure occurs So far is a simplification as - Normal stress only operates at points of particle contact. - Need to account for role of ‘positive pore water pressure’ (effective normal stress) - Cohesion Coulumb-Terzaghi shear strength equation
What are mass movements? Summerfield (1991, p167) Mass movement is the downslope movement of slope material under the influence of the gravitational force of the material itself and without the assistance of moving water, ice or air Gouldie (1994, p321) The modes of a hillslope failure Why not just a landslide? Smith and Petley (2009, p158) The term landslide describes down-slope movements of soil and/or rock under the influence of gravity. Whilst many landslides do occur through the process of rock of soil sliding on a distinct surface, this is not necessarily the case, and thus the term can be something of a misnomer
Selby (1993) to distinguish types should consider - velocity and mechanism of movement, material, mode of deformation, geometry of moving mass, water content. Results of this range of criteria is the existence of many classifications.
Submarine also!! Cruden and Varnes (1996) - Falling: Detachment, limited shear, descend through air (fall, roll, bounce), Toppling: Forward rotation about a point, Spreading: expansion of a material (liquefaction, flow, extrusion), Flowing: Turbulent movement of fluidised (air or water) mass over rigid bed, Sliding: downslope movement of a coherent body over a shear surface
Landslide Behaviour
Behaviour more important???
4 stages of movement
- Prefailure (small displacement, creep, tension cracking)
- Failure (Disturbing forces > Resisting forces, deformations occur until point of failure, peak strength and progressive failure types)
- Post-failure (movement of failed material until it stops,energy loss from overcoming friction, disintegration and acceleration)
- Reactivation (part or all of a stationary, but previously failed mass involved in new movements along preexisting shear surfaces, typically small and slow moving)
Landslide complexes - mosaic features Landslides are dated by eyewitness accounts, remote imagery, absolute and relative dating techniques Activity status is an alternative, looking at movements rather than timing
Landslide Controls (cause and trigger)
Destabilising influences - preparatory factors (changes from stable to marginally stable), triggering factors (changes from marginally stable to actively unstable). Causes - weathering, increase slope angle/ removal lateral support, loading, changes to the water table, removal of vegetation (less soil binding). Triggers - increase in +ve PWP, earthquake shaking, human activity (increased weight)
Lecture Summary
- Defined slopes & outlined progression of research
- Basic geotechnics (material strength, stress, and strain)
- Defined & classified mass movements
- Landslide behaviour (stages of movement, age, activity status)
- Landslide controls (FoS, preparatory and trigger causation)
- Landslide hazard characteristics (phases and value in monitoring!)
- Selected case studies • Aberfan • Randa • Dooncarton • Observe different material, process causation, disaster & success
Mass Movement Hazards
Module: Hazards, Vulnerability and Resilience (GEO5100-20)
University: Bath Spa University
Students also viewed
- Complex Conflicts in Hazard Management
- Exam - Information regarding the exam that took place at the end of the year, provided
- GEO5100-20 Lecture 1 - An introduction to the course, outlining the key concepts and what will be expected
- GEO5100-20 HVR Lecture 2
- Organisations Businesses Env management systems and beyond
- Introduction to Environmental Management