case studies

• Aberfan (21st October 1966) - mudflows

  Mudflows involve the rapid movement of rock and weathered debris mixed with water down slopes. In Aberfan, waste heaps from mining, which are steep hills of unconsolidated rock, were located over a natural spring. After intense rainfall, there was a build up of water in the heap, leading to a mudflow, which destroyed a school, killing 116 children and 28 adults.
• Vallée d'Ossau (2014) - rock falls

  During the winter of 2014, there was a rock fall that closed the road used to access the Gourette Ski Station.

  Causes :

  • shear strength reduction from lubrication due to meltwater penetrating crack systems
  • shear stress increase as freeze thaw expanded cracks which increased the degree to which rocks hung over the cliff
  • human factors such as vegetation removed from cliff face, and undercutting for building roads
• Vaiont Dam, Italy (9th October 1963) - landslide

  Location:

  • 266 m dam built for hydroelectric power
  • deep, narrow, steep sided valley
  • limestone layer over clay

  Causes:

  • when the reservoir was filled water seeped under the top layer, which increased pore pressure and reduced cohesion
  • heavy rainfall

  Event:

  • 270 million m3 of rock slid into reservoir at 25 m/s
  • 100 m high wave went into the valley
  • 2600 people killed
• Holdback Hall (4th June 1993) - rotational slump

  Cause:

  • dry period followed by heavy rainfall
  • clay cliffs became saturated
  • water acted as a lubricant, so the cliff started sliding along lines of slippage
  • destructive waves removed basal support
  • 1 million tonnes of glacial till slid into the sea

  Management:

  • cliff drainage
  • sea wall
  • regrading (only effective measure, but requires lots of space)
  • managed retreat
  • building regulations