Landslides are intermittent and don’t cause as much death and destruction as earthquakes or floods. That’s why the U.S. Geological Survey (USGS) devotes only $3 million a year to landslides and one reason why many states — including Washington — have cut back their efforts, he said.
There’s no federal inventory of landslide-prone slopes, and the existing USGS map dates to 1982. States and counties have lists, but most are incomplete.
Washington’s was compiled without input from a new, laser-mapping technique, which has revealed many previously unknown slide zones.
It’s impossible to monitor every landslide, Moore said. An effective program has to start by singling out the most dangerous ones: those like the Oso slide, which have failed in the past and loom over communities.
With new technologies like laser mapping and satellite imaging, that can be done, said Jonathan Stock, director of the USGS Innovation Center for Earth Science. That more and more communities are expanding into landslide-prone rural and suburban areas adds urgency.
“What people want to know is where the landslides are, when they might happen and how big they might be,” Stock said.
Monitoring can address the “when” question.
The movement that precedes most major slides usually starts slowly, then accelerates as collapse draws near, Moore explained.
“We use displacement trends to predict the time of failure.”
There’s a wide range of instruments that can detect and monitor those trends.
Some of the best are inserted in boreholes where they track what’s going on deep inside a hill.
Devices called inclinometers and tiltmeters can tell when slumping starts and how fast it’s proceeding. Piezometers detect changes in water pressure due to rain and runoff, which can force apart soil grains and weaken the bonds of friction that help keep slopes upright.