Image: Air Support Unit, King County Sheriff's Office
Before the deadliest landslide in America in a decade, geologists had known that the land in Snohomish County, Washington was liable to give way at some point. In fact, geological reports have demonstrated the risks of building in the area since the 1950s. According the US Geological Survey, “large landslides are the norm in many parts of the western foothills of the North Cascades," the Seattle Times reported.
Almost a week after the mudslide, 25 people are known to have died and 90 people are still missing . To prevent something on this scale from happening again, some are asking how to make better use of the new information and maps made with LiDAR—aerial mapping that uses laser pulses fired at the ground from a passing aircraft. It has been used to look for lost cities in the jungles of Honduras thanks to its ability to cut through foliage. It has also been used to discover fault lines in the Pacific Northwest, and reexamine the flood zones of New York Harbor.
“Lidar is like a new pair of glasses,” University of Washington geologist David Montgomery told the Seattle Times. “If you can see more, if you have better data, you can better assess the true risks.”
Lidar can be accurate down to just a few inches, a vast improvement over old topographical surveys done based on aerial photography that, due to tree cover, could only be guesses. But the issue here wasn't one of not knowing. It was who didn't know.
“We’ve got all this great new data,” University of Washington geologist David Montgomery told the Seattle Times. “But if you don’t have anybody to digest it and turn it into information that can get out to the public—it’s just nice data.”
That, though, is the difficulty. Getting an accurate map of the landscape is expensive but possible, yet what’s less understood is how to disseminate the information to the county officials in charge of zoning, and residents of the area, to prevent building more homes in vulnerable areas. That’s part of what’s so frustrating for Pacific Northwest geologists: they didn’t need new technology to tell them that the hill above the town of Oso was susceptible to landslides. The information was even in the public sphere, via a Snohomish County website.
Nevertheless the county believed that it was safe to build homes down by the Stillaguamish River. “It was considered very safe,” John Pennington, head of Snohomish County’s Department of Emergency Management, said at a news conference Monday. “This was a completely unforeseen slide. This came out of nowhere.”
It wasn’t “completely unforeseen” to geologists in the area, nor to the US Army Corps of Engineers who, in 1999, before the area was Lidar mapped warned there was a "potential for a large catastrophic failure.” But somewhere along the line, communication broke down—the right information didn’t make it to the right people, or the full implications of the information wasn’t made clear.
“I hope a lot of counties take a good, hard look at their landscape hazard zones after this,” Dan McShane, an engineering geologist in Bellingham and blogger, was quoted as saying by the Seattle Times.
It's one thing to look, but even that's data. Translating data to action remains is the crucial next step, to mitigate the effects of the next natural disaster.