1. Notable Landslides

2. I. Notable Slides Portuguese Bend Landslide Big Rock Mesa
Bluebird Canyon
Mount Saint Helens
1998 El Niño

3. II. The Portuguese Bend Landslide
Ancient landslide
Bedding dips in same direction as slope (seaward)
Volcanic ash bed => bentonite layer (very slippery!)
Slide reactivated in 1956
Still moving

4. III. Big Rock Mesa Malibu, CA
Rockslide became active in 1983 due to heavy rainfall
0 Fatalities
$1.08 billion in property damage
$706 million (2000 dollars) in legal claims
condemnation of 13 houses, and 300 more threatened
One of the largest and most expensive landslides in the history of the State of California.
Largest law suit ever in the U.S.

5. III. Big Rock Mesa Prehistoric Big Rock Mesa Ancient landslide
Uplift on Malibu Coast Fault & Shoreline Erosion
feet of offset
Failure surface influenced by faulting

6. III. Big Rock Mesa Landslide Stability Water Controls Stability
Dewatering Wells
22 Wells (Twice Monthly Readings)
• Hydrauger (Horizontal Drains)
35 Hydraugers (Monthly Readings)
Slope Movement
Slope Inclinometers
18 Inclinometers (Quarterly)
10 Inclinometers (Twice Yearly)

12. IV. Bluebird Canyon in Laguna Beach, California
October 2, 1978
Unusually heavy rains triggered slide
One of the most destructive landslides of recent U.S. history.
0 Fatalities, $52.7 million in damage
Destroyed or severely damaged 23 homes, associated streets and utilities.
Additional homes and property were in jeopardy
“block glide” or “rock block” slide—a slide with little or no rotational movement.

13. V. Mount Saint Helens March 20, 1980 – Harmonic tremors began
May 18, 1980
5.1 earthquake on nearby fault
caused a massive landslide on the unstable north side
Removal of overburden released pressure and caused the eruption **
5-10 fatalities, $12.3 million in damage

14. VI El Niño Landslides
Increased rainfall amounts in normally dry areas
Intensifies coastal storms
Heavy precipitation caused:
debris flows and landslides in hilly areas
floods along rivers in populated areas
Increased erosion and deposition along the coastline

15. Landslides Ventura Region
Area #2 October 1997
Area #2 April 1998

16. Cliff erosion along the Esplanade Dr. area of Pacifica, CA
Cliff erosion along the Esplanade Dr. area of Pacifica, CA

17. VI. 1998 El Niño Landslides Laguna Canyon Landslide
Heavy rains night of Feb
Numerous small soil slips coalesced into one large debris flow
Crossed over a road and formed a “waterfall” which increased momentum

18.
View looking east at the southern part of upper Castle Rock drainage basin. About nine small soil slip scars are visible in this view. In foreground is Castle Rock channel which has been scoured clean of vegetation rubble by debris flows.

19.
View looking south over the "waterfall". Debris flow mud splattered and coated most of the trees adjacent to the channel as well as high on the side of the three-story house located at the base of the falls.

20.
View looking south on the lower part of the Castle Rock drainage. Debris flows severed and separated a house which was located directly in the path of the debris flows. A short segment of Laguna Canyon Road is seen in the upper right corner.

21.
Close up of the severed house seen in the previous slide. Debris above the severed house is essentially all earth materials & vegetation transported from above the falls; debris below the severed house contains large quantities of household materials.