In landslides, as in life, it's the little things that count. Using a full-scale simulator, researchers have shown that just a small difference in soil density determines whether a landslide becomes a fast-moving killer or merely one that slowly slumps downhill.
In each experiment, the scientists placed 12 tons of soil on a large concrete slab tilted at 31 degrees. That's a typical slope for hills at high risk of landslide, says Richard M. Iverson, a hydrologist with the U.S. Geological Survey in Vancouver, Wash., and lead author of the report in the Oct. 20 Science. The researchers controlled the amount of water in the soil with surface sprinklers and subsurface channels in the concrete.