1. LANDSLIDES VS. MUDFLOWS

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. STEEP SLOPES INCREASE DRIVING FORCE, DECREASE STRENGTH
Yungay, Peru
WHY STEEP SLOPES ?
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. WATER DECREASES STRENGTH BY LOWERING NORMAL FORCE -- “FLOATING”
WHY WATER ?
WATER DECREASES STRENGTH BY LOWERING NORMAL FORCE -- “FLOATING”

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

14. WATER, LOOSE SEDIMENT, STEEP SLOPES
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