Chances May Be High for Slope Failures This Spring

This has been a wetter-than-average water year, and that increases the likelihood for debris flows, debris floods, and landslides in Utah this spring, the Utah Geological Survey says.

"Utah has received more than 170 percent of normal precipitation since October 1996, and surface soils are very moist," says Barry J. Solomon, geologist for the Applied Geology Program of the UGS. "We believe there may be an increased chance of slope failures this spring, even if precipitation decreases. The potential for this will increase if we have a cool, wet spring with a significant late-season snowpack at lower-elevations, followed by a rapid rise in temperatures and snowmelt -- particularly if accompanied by rain."

Two types of slope failures are of concern. Shallow failures are characterized by debris flows and debris floods during heavy rainstorms or periods of rapid snowmelt. They are very fluid, starting most frequently on steep hillsides, then flowing toward canyon mouths by way of existing stream channels. Hillsides recently stripped of vegetation by wildfires are particularly susceptible to shallow failures. Deeper failures are activated after water soaks into hillsides. These failures are larger, less fluid, and generally slower moving and may occur on gentler slopes. Inclines underlain by either clay or shale bedrock, or where landslides have previously occurred, are particularly susceptible to deeper failures.

The UGS has advised the Utah Division of Comprehensive Emergency Management of these conditions.

The Applied Geology Program helps protect Utah's public health and safety by investigating geologic hazards. The UGS, a Division of the Department of Natural Resources, is charged with making Utah richer and safer by generating, interpreting, preserving, and distributing geologic information.