【By HENRY FOUNTAIN／夏嘉玲譯】

SANTA BARBARA, California — Water bottle in hand, Dennis Staley crouched over a patch of ground, cleared away surface soil with a finger and poured a couple of drops on the exposed layer.

Dr. Staley and a colleague, Jason Kean, researchers with the United States Geological Survey, were taking a break from their work one recent morning in Mission Canyon just above Santa Barbara to offer a show and tell on the interaction of soil and water.

“It will soak in on the surface,” Dr. Staley said. “But just below the surface it’s going to bead up.” Sure enough, the water drops were still visible, as if they had been spilled on a tabletop. “So that enhances the amount of runoff that naturally comes off these slopes,” he said.

“Which,” he added, looking at the largely ash-dusted, barren terrain, “is why we do all this.”

For the two scientists, “all this” had included hiking down trail-less slopes of loose rock and soil past sharp, charred stumps of manzanita and oak, hauling gauges and sensors, solar-powered communications equipment, a surveying device with a tripod, and assorted mounting poles, clamps, cables, drills and batteries, as well as cement and other supplies. As part of longterm geological survey research on landslide hazards, they were setting up a remote monitoring station to study how and when the runoff from coming rains might pick up soil and rock and become a destructive torrent of mud.

Given that it was denuded by a wildfire just four months before, Mission Canyon is a likely place for a landslide — in this case, more properly called a mudslide, or, even more properly, a debris flow. In Southern California and other parts of the West, where the wildfires of spring and summer are followed by the rains of fall and winter, slides are the almost inevitable result.

But mudslides and landslides occur all over the world, and often happen in areas with plenty of vegetation.

Last year, according to data compiled by Dalia B. Kirschbaum, a researcher at the NASA Goddard Space Flight Center in Greenbelt, Maryland, at least 540 landslides set off by rain were reported in published accounts around the world. In all, more than 2,100 people were killed.

Given the toll in lives and money, scientists like Dr. Staley and Dr. Kean are studying how and when slides happen — what characteristics will cause a hillside to fail or a flood of mud to roar down a canyon . And Dr. Kirschbaum and others are looking at landslide hazards on larger scales, using data from satellites.

The goal is to be able to assess risk and forecast when disaster looms — locally, regionally, even globally.

Yet landslides do not get as much attention as other disasters, from the public or from scientists. They are usually thought of as secondary hazards, byproducts of much larger catastrophes like earthquakes, fires or storms. They are highly localized events, often occurring in remote, underdeveloped areas. And they can be baffling: one hillside may collapse in a storm while an adjacent one remains intact.

“We have a fundamental problem, really,” said David Petley, a professor of geography at Durham University in England and director of a small research group there, the International Landslide Center. “We understand the process through which these landslides occur incredibly poorly.”

Dr. Petley has maintained a database of fatal landslides since 2002, in part, he said, because knowledge of when and where the slides occur is a step toward understanding them. But another reason, he said, is simply “to demonstrate that landslides have a big impact.”

【2009-11-03/聯合報/G9版/UNITEDDAILYNEWS】