R&W

• Describe the features of a rotational landslide (slump)

  • Steep scar at the top
  • Concave and bowl-shaped at the top
  • Bare scar at the top
  • Small, detached blocks of soil and vegetation at the top
  • Some detached portions on main slide face
  • Bare surface with some indication of rills
  • Main mass of the failure has been removed from the failure surface
  • Initially steep slope and then more gentle
  • Unconsolidated material (scree)
  • Smooth toe at base
• Explain how a rotational landslide is formed.

  • Increased water content by precipitation which leads to a decrease of strength and an increase of stress because of:
  • Greater weight increasing shear stress
  • Increased pore water pressure reducing cohesion and shear strength
  • Lubrication of potential shear surfaces
  • Water erosion for the rill
  • Steep gradient
  • Human interference (removing vegetation)
  • Weakening of material by weathering
  • Undercutting by the sea
  • Earthquake activity
• Describe the global distribution of subduction zones:

  • Around the Pacific Ring of Fire
  • Found where plates converge
  • Small zone along the north-west coast of North America
  • Small zone on the north edge of the African Plate
• Explain how volcanic island arcs are formed:


  • Convergence of two oceanic plates
  • Driven by convection currents in the mantle
  • Subduction of the denser of the two plates
  • Melting of the subducting plate at the Benioff zone
  • Rise of magma through the non-subducting plate
  • To produce volcanic islands
• Name one young fold mountain range that has no active volcanoes.

  Alps
• Compare the distribution of young fold mountains with the distribution of active volcanoes:


  • Volcanoes and fold mountains along the west coast of North and South America
  • Inland fold mountains with few volcanoes, Himalaya, Alps
  • Volcanoes off the east coast of Asia but no fold mountains
  • Volcanoes in the centre of oceans, e.g. Atlantic
• Explain the distribution of young fold mountains:

  • Fold mountains = formed by convergence of tectonic plates, development – driven by convection currents/drag
  • Convergence of (C-C) Eurasian & Indian plates develop.
  • Occurs along major thrust planes, leading to uplift.
  • Accretionary wedges = crushed between plates -> uplift of sediments -> formation of fold mountains