Landscape + Mass Movement

• Karst Landscapes


  Landscape shaped by the dissolution of a layer or layers of soluble bedrock, usually carbonate rock such as limestone
• Limestone landscape needs


  • >80% CaCO3
  • Pre-existing joints
  • Aerated zone
  • Vegetation (organic acids)
• ~15% of Earth's land area has karst features
• Mass Movements

  Any movement of material (soil, regolith, rock) that is driven by gravity
• Material moves downslope due to the pull of gravity
• Mass movements can happen almost anywhere
• Mass movements are commonly associated with other events (heavy rainfall or earthquakes, for example) and are therefore under-reported
• Mass movements

  Can be either catastrophic (slope failure) or slow and steady (creep)
• The rate of the mass movement can be increased by various erosive agents (especially water)
• Driving forces of mass movements


  • Gravity
  • Slope angle
  • Amount of moisture
  • Size, weight, and shape of material
• Resisting forces of mass movements


  • Cohesiveness of material
  • Inertia
  • Friction
• Angle of Repose


  Steepest slope angle where there is a balance between driving forces and resisting forces
• The natural range of the angle of repose is 25–40°
• Larger, more angular material can form steeper slopes
• Triggering mechanisms for mass movements


  • Volcanic eruptions
  • Earthquakes
  • Precipitation
  • Undercut or over-steepened slopes
  • Change in ground water levels
  • Human activities
• Creep


  Very slow movement of sediments down a hill, especially common in areas where freezing and thawing occur (ice wedging)
• Solifluction


  A type of earth flow found in periglacial regions underlain by permafrost, where the surface layer of permafrost melts creating a water-saturated layer that becomes mobile
• Solifluction moves at a rate of about 1-10 cm/week
• Solifluction could result in the high-altitude planation of mountain ranges into flattened summit areas in a process called altiplanation
• Landslide


  Sudden rapid movement of a cohesive mass of regolith or bedrock that is not saturated with moisture
• Flow


  The Addition of water causes instability. Humid climates. Flow as if a thick liquid.
• Avalanche


  Landslides in mountainous areas with thick accumulations of snow, usually occurring on slopes of at least 35 degrees
• Rockfall


  Volume of rock that falls through the air and hits a surface, forming talus slopes
• Debris Avalanche


  Very high velocity movement of rock, debris, and soil
• Fluvial Geomorphology

  The study of landforms created by streams through erosion and deposition
• Fluvial processes


  • Erosion
  • Transportation
  • Deposition
• Drainage basin


  An area of land where all surface water from rain, melting snow, or springs drains into a single river, lake, or ocean
• Characteristics used to describe and classify drainage basins


  • Drainage density
  • Drainage patterns
  • Stream orders
• Sediment transport processes


  • Solution (dissolved load)
  • Suspension (suspended load)
  • Saltation (bounced bed load)
  • Traction (dragged bed load)
• Alluvium


  Sand, silt, clay, gravel, etc. that has been deposited by water in sorted or semi-sorted layers
• Aeolian/Eolian processes


  Wind-related processes of erosion, transportation, and deposition
• Dry (arid) and semi-arid climates occupy 35% of the land surface, and wind has a large impact on erosion and shaping the landscape in these regions
• In deserts, winds can carry more sediment than any other geomorphological agent
• Deflation


  Removal and lifting of loose particles, producing desert pavement and blowout depressions
• Abrasion


  Grinding/wearing down of rock surfaces through sandblasting by particles suspended in the air
• Methods of aeolian sediment transport

  • Saltation (bouncing)
  • Creep (rolling/sliding)
  • Suspension (fine particles in turbulent air)
• Saltation accounts for ~80% of aeolian sediment transport
• Creep accounts for ~20% of aeolian sediment transport
• Geomorphic Threshold 


  Gravity pulls on a mass until the critical shearfailure point is reached
• Scarification 


  Human-induced induced mass movements. Slopes become destabilized due to human activity such as roads, construction, and mining