California Landslide Part of Ancient Problem

A landslide that killed 10 people and destroyed some 30 homes in La Conchita, California in January was part of a much larger slide that dates back to prehistoric times, according to a new study.

Larry Gurrola, geologist and graduate student at the University of California, Santa Barbara, discovered the ancient feature, now called the Rincon Mountain slide. It started many thousands of years ago and will continue generating slides in the future, Gurrola was to tell the national meeting of the Geological Society of America today.

A landslide also struck La Conchita in 1995.

"The question is not if but when the next landslide will impact the community of La Conchita," Gurrola says. "A combination of factors makes future landslides inevitable. These are: active faulting and folding; rapid tectonic uplift; very weak rocks; steep topography; and, the presence of springs."

Prolonged, intense precipitation seem to trigger specific slides, the study found, confirming scientists' preliminary explanation earlier this year. The larger, complex slides may increase in activity months or even years after wet years. An earthquake could also trigger a slide.

This past winter was among the wettest on record in many parts of Southern California.

"Landslides similar or larger than the 1995 and 2005 events may occur next year or in coming decades, during or shortly after intense rain," Gurrola said. "People tend to have short memories when it comes to geologic hazards such as landslides. If people continue to live in La Conchita, more lives will be lost in the future."

Gurrola and Edward Keller, professor of earth science at UC Santa Barbara, suggest that property owners be fairly compensated for their property and that the site be made into a beach park.