Expert say few rockfalls can be prevented
By Mike Leidemann
Advertiser Staff Writer
When geologist Greg Moore looks out his window in Manoa, he can see more than 100 homes with potential rockfall problems.
Multiply that by all the ridges and valleys in Hawai'i, and there are thousands of people at risk of being hit by a rockslide or blamed for causing one, he says.
There's not much help or consolation he or anyone else can offer them. The good news is that their chances of being hit are small.
Moore and others experts said yesterday there is little that can be done, practically or economically, to prevent loose boulders from crashing down hillsides into residential areas, as some people say is happening with increasing frequency in Hawai'i.
"That's simply the way volcanoes weather," said Moore, a University of Hawai'i professor of geology and geophysics. "This has been going on from day one, 2 1/2 million years ago. The difference is there are a lot more homes around now."
Homeowners wondering about their chances of being caught in, or causing, a landslide have few places to turn for help, officials said yesterday as state engineers evaluated a Nanakuli hillside where a car-sized boulder rolled into a home Thursday night. It was the latest in a series of accidents in recent years in Kailua, Hawai'i Kai, Nu'uanu, Punchbowl and elsewhere.
Available solutions probably cost more than they are worth.
Engineers said a thorough examination can run from $40,000 to $80,000, and only tell most homeowners what "probably" will happen. Potential mitigation measures can cost from $15,000 up, depending on the size lot to be protected.
Moreover, many geologists won't undertake such evaluations because of mounting concerns about legal liability.
"You're damned if you do and damned if you don't," said one engineer who said company policy prevented him from being identified. "If you say there is a problem, the guy at the top of the hill will sue you. If you say there's no problem, the guy at the bottom will sue you."
While government officials have resources to help when a problem originates on public property, there's little they can do to help private homeowners assess risks and avoid problems.
"This might be a good time to point out that Hawai'i is the only state in the country that does not have a state geological survey office," Moore said. "In other states, you could go there for advice and help. We don't have that."
Robin Lim, a geotechnical engineer with the Honolulu firm Geolabs, suggests that homeowners worried about a rockfall problem skip the expensive evaluation and start in on protective measures.
"Take the money you'd spend on an engineer and instead hire a contractor who knows what he's doing to build a rock-catching fence," Lim said. It won't reduce all danger, but it might catch small boulders and slow down a bigger one enough to prevent more serious damage.
Depending on the situation, other mitigation measures might include applying mortar to crumbling rock faces, covering rock faces with wire mesh or moving or destroying a boulder, said Steve Martel, a UH-Manoa geologist and landslide expert.
Lim said people who buy or build their homes at the bottom of eroding mountain ridges need to share responsibility for what happens when a boulder crashes into their neighborhood.
"When a rock crashes into a car on a state highway, the state gets some of the blame for where it put the highway. It's the same thing with a house. If you are the homeowner, you have to take some responsibility."
Ultimately, the only way to stop the problem entirely is to keep people from building homes at the top or bottom of the state's many ridges, Moore said.
"You can't deny that there's a problem, and you can't deny that it's going to keep happening. It's the law of averages," he said.
Reach Mike Leidemann at 525-5460 or mleidemann@honoluluadvertiser.com.
