CLAY MOBILITY, PORTUGUESE BEND, CALIFORNIA
COLUMBIA UNIV NEW YORK DEPT OF GEOLOGY
Pagination or Media Count:
The south slope of Palos Verdes Hills west of San Pedro, California, in the area known as Portuguese Bend contains an unusual landslide. The slide movement takes place in members of the Monterey Shale which contain bentonite particularly the Portuguese Tuff. Samples of bentonite from the tuffaceous rocks are rich in Ca-montmorillonite which has definite thixotropic properties. When dry the clay is stable, but with the adsorption of water it swells and may ultimately flow. Overlying shale masses although substantial in themselves are slowly rafted down sloped on the underlying bentonite-lubricated slip plane. Movements have frequently been measured in terms of a small fraction of an inch per day, but during a year cumulative movement in places may amount to 10 to 30 feet. The physical properties of the clay have been studied in considerable detail and reveal a mobile material. Field observations indicate that enlargement of the slide area is also in constant progress. No field control of this situation has yet been established.
- Geology, Geochemistry and Mineralogy
- Soil Mechanics