Rains Long Gone but Landslides Still Possible, Geologist Says

After one of the wettest years on record, Southern California has been hit by a rash of landslides. Former state geologist James Slosson, now a private consultant working for Calabasas and Agoura Hills, says that nearly all of these slides could have been avoided through careful geology tests and sound engineering. Slosson was interviewed by Times Staff Writer Aaron Curtiss.

Q: What makes Southern California so prone to landslides?

Youthful geologic conditions. Associated with that are coastal bluff failures, landslides and earthquakes.

Certain types of rock materials also are much more susceptible to landslide activity than others.

Q: Such as?

Some of the relatively youthful shale type of rocks typical to parts of the Malibu area and the Santa Monica Mountains. The shale contains clay which changes strength when it gets wet, and it is very susceptible to slope failure.

Q: When a slope fails, what happens?

In almost every case, it is associated with saturation from rainfall. This year we are at about 200% of average or normal rainfall.

Q: The ground just gets too heavy to stay put?

The water increases the weight. Water also causes some of the clay materials to lose strength.

If you’ve ever walked on a dry slope in the summertime, when the ground is relatively firm, you could walk without slipping. Try to walk on that same trail during a rainstorm, and you have a hard time just standing up. The same thing happens with rock.

Also, as water seeps through rock, it exerts pressure.

Q: Even after the rainy season, though, the danger of slides still exists, right?

Once water gets into the ground and into the rock, it moves quite slowly. In some cases the rate of seepage is only a few feet or a few hundred feet per year. So we could have failures for up to six months after the rainy season.

Q: If a potential buyer is looking at a house in an area that looks prone to slides, is it wise to request the geology reports and have them reviewed?

Yes, but then you have a problem because you will hire someone recommended by a realtor.

How do you choose? About all you can do is go to the yellow pages, since there is no peer review. The geology licensing board has never in over 20 years taken a geologist to task for being involved in these types of failure.

A buyer should go to the courthouse and see who has cases against them and check to see why.

Q: So a buyer essentially just has to keep his fingers crossed and hope for the best ?

Yes, and you have no insurance. You cannot get landslide insurance as part of a homeowners policy. The insurance industry made a unilateral decision on that at the time of the Portuguese Bend landslide in the mid-1950s.

Q: So should we all live in the flatlands?

Then you’ve got the problem with flooding.

The insurance industry should be pushed or encouraged to provide coverage. It would be possible to develop insurance similar to fire insurance for brush-covered areas.

Q: Would such an action make builders more careful?

I know damn well it would. If the insurance companies have to pay out an insurance claim, they will find out who did what wrong. Their staff of attorneys will be much more successful than some homeowner hiring an attorney.

Q: How can someone in an area prone to sliding make sure that slopes around them won’t fail?

The very elementary approach is that certain rock materials in the mountains are more susceptible to problems than others.

There are maps which estimate the relative amount of landslides based on rock type, both of which are controlled somewhat by rainfall. In Southern California it’s only when the rainy-season total exceeds 20 inches that these problems really start to show up.

Q: If it’s common knowledge that these areas are prone to failures, why is building allowed there?

Now you get into another problem, which is the economics.

If the value of the land is extremely high because of the neighborhood and scenic beauty, a lot of these problems are overlooked.

Q: Who overlooks them? The developer? The local government?

Local government is responsible for requiring reports on the hazard and its mitigation. But local government is immune for its action. It has no responsibility if something goes wrong, unless it’s a failure of a public street or water line.

Q: And the developer can be held liable for only 10 years, right?

Right. And as long as the consultant has complied with what is referred to as a standard of care, then he is essentially off the hook.

Q: What is standard of care?

If the local government accepts the report, then it has met the standard of care.

Q: So it goes back and forth.

Yes. One of my most often repeated quotes is that the standard of care will fall to the lowest level allowed by government.

It’s sort of like the puppy chasing his tail. Since the governmental people are immune from whatever they do and the consultants doing the work are essentially home free if government accepts the report and you have to prove negligence to hold the consultants responsible, where are you?

We have more knowledge than we have ever had. We have more technology, better instruments, better equipment. And the failures and dollar losses are increasing. If this were the medical profession, there would be a federal study.

Q: You have said that if a slope is properly engineered and graded it will not fail.

If it is properly analyzed and properly designed and there is proper maintenance, which includes the drainage and not allowing water to pond . . . the failure factor drops by an average of 95%.

Q: So builders are playing a game of Russian roulette?

It’s Russian roulette with all the cylinders loaded. The only question is what year it is going to happen.