UNSTEADY HILLSIDES CAN STILL LET LOOSE, WARN GEOLOGISTS.

Byline: Kerry Cavanaugh Staff Writer

After reviewing soil studies, slope measurements, rainfall figures and old photos, geologists warned Tuesday that Los Angeles and Ventura County hillsides remain susceptible to slides - and the risk could last for weeks - especially if the rain continues.

``If we get a repeat of what we've had, then we're going to see an amazing number of debris flows,'' said Doug Morton, a research geologist based at the U.S. Geological Survey's office in Riverside.

Landslides happen when all the spaces in sediment fill with water. The top foot of soil becomes so saturated and heavy it slips downhill.

And it's not just the quantity of precipitation that causes slippage, experts say.

``It's the pattern of rainfall. We've had light to moderate rain since December. You're filling in the pores with water,'' said Amalie J. Orme, professor of geography at California State University, Northridge.

``We had the perfect circumstances for land movement.''

The soil type and vegetation also can play a role in slide risk. Generally, if a hillside slides once it's likely to slide again.

``La Conchita ... has moved historically in the past and it's an area of unstable sediments,'' she said. ``But in a sense, people forgot about it.''

But not the USGS researchers, who spend much of their time fine-tuning their landslide model based on hundreds of thousands of Southern California slides over decades.

By adding current weather information, the USGS develops maps to highlight the riskiest slopes, and to warn people when the landslide possibility turns into a probability.

Kerry Cavanaugh, [phone]

kerry.cavanaugh(at)dailynews.com