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MASS WASTING

MASS WASTING. SURFICIAL PROCESSES. Erosion, Transportation, Deposition on the Earth’s Surface Landscapes created and destroyed Involves atmosphere, water, gravity Agents: Mass wasting (gravity), Running water (streams), glaciers (ice), wind, water waves, ground water. MASS WASTING.

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MASS WASTING

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  1. MASS WASTING

  2. SURFICIAL PROCESSES • Erosion, Transportation, Deposition on the Earth’s Surface • Landscapes created and destroyed • Involves atmosphere, water, gravity • Agents: • Mass wasting (gravity), Running water (streams), glaciers (ice), wind, water waves, ground water

  3. MASS WASTING • Masses of debris (mud, sand, gravel) or bedrock moving downhill • Landslides and slower movements • Driven by GRAVITY

  4. Classification of Mass Wasting • RATE of MOVEMENT • Extremely slow (~1mm/year) to very rapid (>100 km/hour) • MATERIAL • Bedrock • Debris- (“soil”, sediment)

  5. Classification of Mass Wasting • TYPE OF MOVEMENT • Flow • Slide • Translational slide • Rotational slide (Slump) • Fall

  6. Controlling Factors • Slope angle- gentle vs steep • Local relief- low vs high • Thickness of debris over bedrock- slight vs great • Planes of weakness ( in bedrock) • bedding planes; foliation; joints • planes at right angle to slope vs parallel to slope most dangerous

  7. ANGLE OF REPOSE

  8. Controlling Factors • Climatic controls • Ice- above freezing vs freeze & thaw • Water in soil- film around grain vs saturation • Precipitation- frequent but light vs periods of drought and heavy rainfall • Vegetation- heavily vegetated vs light or no vegetation • Gravity • Shear force- parallel to slope, block’s ability to move • Normal force- perpendicular to slope, block’s ability to stay in place due to friction • Shear strength- resistance to movement or deformation of debris

  9. The Effect of Slope & Gravity G=gravity S=shear F=friction N=normal F S G N

  10. Controlling Factors • Water • adds weight • increased pore pressure in saturated debris decreases shear strength • surface tension in unsaturated debris increases shear strength • Triggering Mechanisms • Overloading • Undercutting • Earthquakes

  11. Common types of mass wasting • CREEP • gentle slopes • vegetation slows movement • very slow flow (< 1 cm/year) • facilitated by water in soil • or by freeze-thaw in colder climates • Indicators of creep • ‘pistol butt’ trees • leaning tombstones, walls, posts

  12. Solifluction & Permafrost • Solifluction: • Flow of water saturated debris over impermeable material • Permafrost: • Ground that remains frozen for many years

  13. Common types of mass wasting • DEBRIS FLOW • Motion taking place throughout moving mass • Includes • Earthflow • Mudflow • Debris Avalanche

  14. Earthflow • Primarily flow of debris • may involve rotational sliding • Scarp above • Hummocky surface in lower part • May be slow or fast • Solifluction • role of Permafrost in cold climates

  15. Mudflow • Flow of watery debris • Occurs where lack of vegetation: • Dry climates • Volcanoes • After forest fires

  16. Debris Avalanche • Very rapid, turbulent flow of debris • mud-boulders • >150 km/hr • Triggered by • volcanic eruptions- Mt. St. Helens 1980; Nevado del Ruiz 1985 • intense rainstorms- Venezuela 1999 • earthquakes- Japan 2000

  17. Rockfalls and Rockslides • Rockfall • Bedrock breaking loose on cliffs • Talus at base of cliffs • Rockslide • Bedrock involved • Sliding along planes of weakness parallel to slope • Bedding planes; foliation planes; fractures in rock (joints)

  18. Debris Slides and Debris Falls • Debris fall • Free-falling mass of debris • Debris slide • Debris moving along a well-defined surface

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