As searchers look for the last of the missing in Oso, Washington, where a massive landslide virtually wiped out the small community, it’s becoming more obvious that authorities knew about but failed to fully heed the warnings of scientists that such a disaster was a real threat.

Not only that, they even considered – but then rejected – a suggestion that they buy out home and business owners whose properties lay just across the Stillaguamish River from a steep hill that had fallen away several times before.

The Seattle Times newspaper reported this week that Snohomish County officials analyzed the situation, finding that the costs of a buyout “would be significant, but would remove the risk to human life and structures.”

Instead, they decided to build a wall intended to stabilize the slope, leaving existing structures in place and allowing more to be built. Eight people in those newer homes are dead or missing from the landslide, including four children, the newspaper reported.

Experts studying the most recent slide – and the several that preceded it over the years, particularly one in 2001 – say this was a fatal mistake.

“[T]o my mind this was [a] foreseeable event, and as such the disaster represents a failure of hazard management,” writes Dave Petley, a professor of hazard and risk at Durham University in the United Kingdom and author of The Landslide Blog, which is hosted by the American Geophysical Union.

“The 2001 landslide left material high on the hillside that was sitting above a scar that was far too steep,” Dr. Petley writes. “The LIDAR [Light Detecting and Ranging] data suggests that the runout from such a collapse could be extensive. In that context I find the decision to build new houses at the foot of the landslide to be very surprising.”

In retrospect, some residents in the area are surprised as well … some of them furious that they weren’t warned of the threat.

Davis Hargrave, a retired architect who lost dozens of neighbors and his weekend home, said knowing the county took the threat as seriously as it did would have prompted him to ask many more questions.

“We are not a bunch of stupid people ignoring warnings,” Mr. Hargrave told the Seattle newspaper. “We all make risk assessments every day of our lives. But you cannot make a risk assessment on information you do not have.” (...)