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LANDSLIDES VS. MUDFLOWS

LANDSLIDE. LANDSLIDES VS. MUDFLOWS. MUDFLOW. What is a Landslide?. Slide. Venuzuala, Coast Road. Where do Landslides Occur?. Three major controls. WHAT CAUSES LANDSLIDES? STEEP SLOPES AND WATER. WHY?. Why do landslides occur?. Strength of rock/soil exceeded. DRIVING force. >>.

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LANDSLIDES VS. MUDFLOWS

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  1. LANDSLIDE LANDSLIDES VS. MUDFLOWS MUDFLOW

  2. What is a Landslide?

  3. Slide Venuzuala, Coast Road

  4. Where do Landslides Occur? Three major controls...

  5. WHAT CAUSES LANDSLIDES?STEEP SLOPES AND WATER. WHY?

  6. Why do landslides occur? Strength of rock/soil exceeded DRIVING force >> RESISTING force DRIVING force RESISTING force

  7. FORCE BALANCE DRIVING VERSUS RESISTING FRICTION AND COHESION GRAVITY

  8. Simple Physics……vectors • DRIVING force is gravity, • RESISTING force is soil/rock strength/friction • Steep slopes give greater Driving Force

  9. Yungay, Peru WHY STEEPSLOPES ? STEEP SLOPES INCREASE DRIVING FORCE, DECREASE STRENGTH

  10. GREATER THE NORMAL FORCE THE GREATER THE RESISTING FORCE What is normal anyhow? FRICTION AND COHESION GRAVITY NORMAL FORCE

  11. What does slope have to do with normal forces????? LENGTH OF VECTOR = MAGNITUDE Can demo dry TAKE HOME MESSAGE: Steep slopes reduce normal force and thus resistance to sliding

  12. WHY WATER ? WATER DECREASES STRENGTH BY LOWERING NORMAL FORCE -- “FLOATING”

  13. SUBTRACTING VECTORS FORCE BALANCE TIPS BOUYANCY FORCE WET NORMAL FORCE IF DRY

  14. San Rafael,CA WATER, LOOSE SEDIMENT, STEEP SLOPES WHAT CAUSES MUDFLOWS?

  15. HOW DO MUDFLOWS WORK? • Intimate mixture of sediment and water • OFTEN start from landslides • One phase flow • Move under gravity force • Have a yield strength -- plastic behavior • Stop when they get too thin or slope lessens -- DRIVING vs. RESISTING FORCES

  16. Three phases of a mud/debris flow.. Bouldery snout Watery tail Mud and rock middle

  17. MUD AND DEBRIS FLOWS LEAVE DIAGNOSTIC CLUES • Bouldery snouts -- frozen on low slope • Marginal levees -- too thin to keep flowing, bouldery • Unsorted sediments -- not enough water to sort material levee snout v levee

  18. Bouldery Snouts Sierra Nevada, Lone Pine, Owens Valley

  19. Marginal levees RV for scale Sierra Nevada, Lone Pine, Owens Valley

  20. Unsorted sediments

  21. WHERE ARE MUDFLOWS MOST LIKELY TO STRIKE? ANY WHERE WITH STEEP SLOPES, VERY HEAVY RAIN, AND LOOSE SEDIMENT... THIS INCLUDES DESERTS, THE ARCTIC, AND THE TROPICS.

  22. DESERT EXAMPLE, SIERRA NEVADA, CALIFORNIA

  23. MELVILLE ISALND ARCTIC EXAMPLE. CANADA

  24. WHAT SETTINGS EXACERBATE MUDFLOW HAZARDS?

  25. Valleys NEAR VOLCANOES are risky places to be

  26. WHAT ARE MUDFLOW DANGERS? Erosion then deposition

  27. INFRASTRUCTURE DISRUPTION VERDUGO HILLS CEMETARY, Glendale California Apartments, Venezuela

  28. BURIAL LOS ANGELES

  29. Debris Delivery

  30. USGS Debris Flow Video

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