Thursday, October 4, 2007

Landslides, nature, and the blame game

There was a big landslide yesterday near San Diego, California. Landslides in coastal California are not at all uncommon – the mountains are steep, and young, and many of them are made of rock that falls apart easily. So I wasn’t surprised to hear about it, but my students asked about it this morning, so I looked it up on CNN.

And at the bottom of the story, I found this:

Pat Abbott, a retired geological sciences professor at San Diego State University, told the Union-Tribune that Mount Soledad is made up of weak layers of rock and that the culprit in the landslide is nature.

Now, a bit of background may be in order here. Local residents are blaming the city for the landslide – they claim that the city didn’t repair leaky pipes, including a fire hydrant, and that the water caused the landslide. So Abbott pointed out the geologic background of the area, which makes it particularly prone to landslides: the mountain is underlain by weak layers of sedimentary rock that slope in the same direction as the hillside. In other words, the hillside was going to slip someday. (In fact, there was a landslide in the 1960’s when the area was first developed, and there were two landslides in the 90’s.)

But the quote on CNN’s web page doesn’t go into that background. Instead, it simply says “the culprit... is nature.”

There’s something about that statement that suggests the inevitable, the uncontrollable, the unpredictable. There’s nothing we can do. It’s natural. It reminds me, actually, of statements by Robert Murray, owner of the Utah mine that collapsed in August. (He tried to avoid blame by arguing that the collapse was natural - in that case, that it was the result of an earthquake.) If nature is at fault, then how could a mere human have done anything?

But I don’t buy that. Nature isn’t wholly unpredictable. Sunrise and sunset are natural. So are tides. And so, for that matter, is gravity... which is ultimately the cause of both landslides and mine collapses. Now, the response of earth materials (be they coal or soil) can be difficult to predict, but that doesn't mean we know nothing - it simply means that we can’t draw a single clear line between “safe” and “unsafe.” And hillsides that have slid before fall into the category of “probably unsafe... eventually.”

So do I think the city is responsible? Probably not (although adding water to a dangerous slope could change a slope from “potentially unstable” to “oh s*** let’s get the heck out of here”). But I don’t think that a sense of fatalism is the only other possible response.

Nature can be dangerous. And it’s more dangerous in some places than others. And we already know a lot about where those places are.

So maybe people should pay attention to dangerous geology. On steep hillsides, yes, but also in flood plains, and along coasts. Because losing a house is horrible and tragic, and it would be better to avoid it happening in the first place.

Pat Abbott (who is also the author of a textbook on natural hazards) knows this, by the way. The CNN story ends like this:

"Gravity pulling on the incline is pulling down masses of earth and those masses of earth have houses on top of them," Abbott told the paper. "It's a geologically bad site and should not have been built on to begin with."


Anonymous said...

"And so, for that matter, is gravity... which is ultimately the cause of both landslides and mine collapses."

You're nicely foreshadowing my Accretionary Wedge #2 post.

nice post...well said

Chris R said...

Do you know if the risk of landslides has ever been assessed by the city authorities? If they granted planning permission without (or in spite of) a proper risk assessment, the residents may have a case.

Of course, even I've heard about the landslide risk in coastal California, so it's not exactly obscure knowledge ...

Kim said...

Brian - I'm looking forward to reading your post!

Chris -

I don't know much about San Diego (or, technically, La Jolla) city government. But there's an article about existing landslide info here.

The USGS published a map that showed landslide hazards in the area in 1995. If there were housing developments in the area in the 1960's, that would have been too late for the city to have prevented building the houses in the first place.

But there's another issue that's important in a lot of US communities - some groups consider it unconstitutional to prevent a private property owner from developing his/her land - at least without the government paying the property owner for the value of the land. The power of those groups varies from state to state, so there's a lot of variation amongst land use laws in the US. (The one exception is in flood zones - there is a national law that deals with flood insurance and, so some extent, with flood plain development.) But attempts to prevent people from building on unstable slopes, or on barrier islands, on in other clearly hazardous areas tend to be quite controversial in the US.

So I'm not sure that the city could legally have prevented the development even if they understood the hazards. (I don't know California law.)