The Free Press, Mankato, MN

State, national news

April 7, 2014

Early-warning tools to scan for slides rarely used in Northwest

(Continued)

Other instruments scan the landscape for deformation. The same laser method used for aerial maps, called lidar (light detection and ranging), can be deployed on the ground to detect tiny bulges or slumps. GPS sensors can serve the same function. The newest ground-based radars are able to discern millimeter-level shifts.

The more intensive the monitoring, the higher the price tag.

Mining operations lead the way in landslide monitoring, because they have so much at stake, Moore said. A single ground-based radar can cost $250,000, and the Utah mine used six to pinpoint the timing of last year’s slide.

But it’s possible to devise a basic system that’s much less pricey, Moore said. In some Swiss valleys, surveyors take readings once or twice a year and only step up their efforts if they detect anything alarming.

Cheaper options are also in the pipeline. Engineers in Switzerland are developing wireless GPS instruments that can be linked in a network and cost about a thousand dollars.

Neil Dixon and his colleagues at the University of Loughborough in the U.K. are testing an acoustic system that provides continuous monitoring for an initial investment of less than $10,000.

Called Slope ALARM, it’s basically a metal pipe sunk into a hillside and filled with gravel. As the slope slips, the gravel rumbles; specially tuned sensors pick up that sound. The noisier it gets, the greater the chance of failure, Dixon explained.

At some predetermined threshold, the system sends out warnings.

Experts caution that there’s no way to know whether a monitoring system in Oso could have prevented the loss of life. Any effective warning system requires an understanding of the slope and its dynamics, Dixon said.

“None of these instruments are magic wands. You need engineering and geologic assessments … to even decide where to put your instruments,” Dixon said.

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