UNL geologist warns of potential for landslides from recent rains
July 6, 2010
LINCOLN, Neb. – Recent rain over much of Nebraska may increase the danger of property-damaging and potentially life-threatening landslides in parts of the state where waterlogged soil overlays hard shale or clay.
“We certainly have the potential for more landslides across the state, due to our recent heavy rains, particularly in areas that are prone to them,” said retired University of Nebraska-Lincoln research geologist Duane Eversoll.
Hundreds of landslides have occurred in Nebraska and though they don’t have the visual drama of those in say, California, or the make-believe movie variety that devastate everything in their path, they do threaten roads, homes, utilities and possibly lives throughout Nebraska.
“Right now we have all the elements in place that can cause landslides. Geological formations prone to landslides, such as the Pierre Shale in northeastern Nebraska that contains clay soils that expand when wet, or loess soils overlaying glacial materials mainly in eastern Nebraska; slope – even five degrees or less; and plenty of precipitation, which increases pressures within the mass and also adds weight,” the longtime Conservation and Survey Division geologist said.
When those conditions are met, slides can occur on their own, or following a suitable “trigger” such as a clap of thunder, a heavy truck bouncing down a roadway, or an earth tremor.
When landslides occur in Nebraska, they often destroy or cover sections of roads, break buried utilities, destroy utility poles, cause depressions in the earth and have other adverse effects.
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Landslides occur mostly in eastern Nebraska’s glacial soils that are overlaid by loose loess soil and exposed Pierre shale, a type of clay that occurs at intervals statewide, but they historically cause the most damage in northeast Nebraska, Eversoll said. Only the Sandhills are relatively immune from landslides.
They are particularly common along the Niobrara River, where Pierre Shale is exposed, and in many parts of eastern Nebraska, where one of the prominent geologic formations is glacial clay overlaid by loess soil.
Rain increases the pore pressures within the soils and adds weight to soils causing it to destabilize. As a result, much of the state currently has a higher risk for landslides due to the recent and repetitive heavy rainfalls, he said.
“No major slides have been reported but there is very high probability for them and that will continue for as long as soils are saturated with water,” he said.
Although retired, Eversoll remains active tracking and recording Nebraska landslides and is one of the state’s foremost experts on them, having carefully studied them for more than 30 years.
Much of his work was done to help predict where slides are most likely and to minimize damage from them by planning roadways and housing developments away from the most slide-prone areas.
Much of Eversoll’s research was done in cooperation with the Nebraska Department of Roads, which has spent hundreds of thousands of dollars controlling and stabilizing landslides, and fixing their damage.
An acute example is Nebraska Highway 14 near the South Dakota border south of Niobrara. A stretch of the road above an active slide has been repaired so many times the asphalt was more than eight feet thick before the roadway was relocated around the landslide area.
Homes built along river bluffs can be particularly susceptible to slides when trees are cleared, lawns planted and watered, and pools and septic systems added.
“Development disturbs established vegetation that stabilizes a bluff or slope and of course adding additional water, often becomes a recipe for disaster,” Eversoll explained. Homes in many parts of the state, including near Fremont, Omaha, Elkhorn and the Panhandle’s Wildcat Hills, are susceptible.
“With all the elements currently in place that produce slides, it’s just something to be aware of and that we can expect more of until things begin to dry out.”
For more information on Nebraska’s landslides, including detailed information on individual slides, go online to UNL’s School of Natural Resources at http://snr.unl.edu/data/geologysoils/landslides/landslidesdatabase.asp.