I. Notable Slides

• A. Portuguese Bend Landslide
  
• B. Big Rock Mesa
  
• C. Bluebird Canyon
  
• D. Mount Saint Helens
  
• E. 1998 El Niño

II. The Portuguese Bend Landslide

• A. Ancient landslide
  
• B. Bedding dips in same direction as slope (seaward)
  
• C. Volcanic ash bed => bentonite layer (very slippery!)
  
• D. Slide reactivated in 1956
  
• E. Still moving

I. Notable Slides | II. The Portuguese Bend Landslide | III. Big Rock Mesa | IV. Bluebird Canyon | V. Mount Saint Helens | VI. 1998 El Niño Landslides | Links | top | Geol 357 Lecture Home

III. Big Rock Mesa

• A. Malibu, CA
  
  • 1. Rockslide became active in 1983
    • a. 0 Fatalities
    • b. $1.08 billion in property damage
    • c. $706 million (2000 dollars) in legal claims
      
    • d. condemnation of 13 houses, and 300 more threatened
      
  • 2. One of the largest and most expensive landslides in the history of the State of California.
    
    • a. Largest law suit ever in the U.S.
      
• B. Prehistoric Big Rock Mesa
  
  • 1. Ancient landslide
    
  • 2. Uplift on Malibu Coast Fault & Shoreline Erosion
    
  • 3. 200 - 300 feet of offset
    
  • 4. Failure surface influenced by faulting
    
• C. Landslide Stability
  
  • 1. Water Controls Stability
    
    • a. Dewatering Wells
      
      • 1) 22 Wells (Twice Monthly Readings)
        
    • b. o Hydrauger (Horizontal Drains)
      
      • 1) 35 Hydraugers (Monthly Readings)
        
  • 2. Slope Movement
    
    • a. Slope Inclinometers
      
      • 1) 18 Inclinometers (Quarterly)
        
      • 2) 10 Inclinometers (Twice Yearly)
        

I. Notable Slides | II. The Portuguese Bend Landslide | III. Big Rock Mesa | IV. Bluebird Canyon | V. Mount Saint Helens | VI. 1998 El Niño Landslides | Links | top | Geol 357 Lecture Home

IV. Bluebird Canyon in Laguna Beach, California

• A. October 2, 1978
• B. Unusually heavy rains triggered slide
• C. One of the most destructive landslides of recent U.S. history.
  • 1. 0 Fatalities
  • 2. $52.7 million in damage
    
  • 3. Destroyed or severely damaged 23 homes, associated streets and utilities.
    
  • 4. Additional homes and property were in jeopardy
    
• C. “block glide” or “rock block” slide—a slide with little or no rotational movement
  

I. Notable Slides | II. The Portuguese Bend Landslide | III. Big Rock Mesa | IV. Bluebird Canyon | V. Mount Saint Helens | VI. 1998 El Niño Landslides | Links | top | Geol 357 Lecture Home

V. Mount Saint Helens

• A. March 20, 1980 - Harmonic tremors began
  
• B. May 18, 1980
  
  • 1. earthquake on nearby fault
    
  • 2. caused a massive landslide on the unstable north side
    
  • a. one of the largest landslides in historic times
    
  • 3. Removal of overburden released pressure and caused the eruption
    
  • 4. http://pubs.usgs.gov/publications/msh/catastrophic.html
• 5-10 fatalities, $12.3 million in damage
  

I. Notable Slides | II. The Portuguese Bend Landslide | III. Big Rock Mesa | IV. Bluebird Canyon | V. Mount Saint Helens | VI. 1998 El Niño Landslides | Links | top | Geol 357 Lecture Home

VI. 1998 El Niño Landslides

• A. Increased rainfall amounts in normally dry areas
  
  • 1. Intensifies coastal storms
    
  • 2. Heavy precipitation caused:
    
  • 3. debris flows and landslides in hilly areas
    
  • 4. floods along rivers in populated areas
    
  • 5. Increased erosion and deposition along the coastline
    
• B. Laguna Canyon Landslide
  
  • 1. Heavy rains night of Feb 23 1998
    
  • 2. Numerous small soil slips coalesced into one large debris flow
    
  • 3. Crossed over a road and formed a "waterfall" which increased momentum
    
  • 4. http://geology.wr.usgs.gov/wgmt/elnino/scampen/laguna/index.html
    

I. Notable Slides | II. The Portuguese Bend Landslide | III. Big Rock Mesa | IV. Bluebird Canyon | V. Mount Saint Helens | VI. 1998 El Niño Landslides | Links | top | Geol 357 Lecture Home