Most individuals know what steps to take when the National Weather Service forecasts a winter storm: head to the store for groceries, and maybe a container of ice and snow melt. But when it comes to the potential for landslides, few in Western North Carolina know what actions to take and when to take them. How to accurately predict a potential landslide is a challenge as well. That may soon change.
Three houses were damaged in Haywood County when a retaining wall failed and debris flowed downslope Feb. 5. The incident was triggered by a wet January, in which eight inches of snow fell at the end of the month, followed by rain. Geologists and meteorologist from a four-state region are working to predict potential landslides and how to warn residents and emergency personnel about that risk. (Photo courtesy of the N.C. Geological Survey).
Appalachian State University hosted meteorologists from the National Weather Service’s (NWS) regional offices in Blacksburg, Va., and Greer, S.C., geologists from the U.S. Geological Survey, Kentucky Geological Survey, Virginia Division of Geology and Mineral Resources, and N.C. Geological Survey (NCGS) in the N.C. Department of Environment and Natural Resources (NCDENR), and N.C. Emergency Management representatives to discuss the best ways to use data to predict the potential of landslides along steep slopes and how to alert residents in a timely manner about the dangers of landslides following significant rainfall.
The workshop, “Landslides and Weather: Anticipating the Hazard-Communicating the Threat,” was designed to provide a forum where the scientists could discuss the limitations of their data and move toward constructing a more useful model or approach to providing landslide warnings, explained Dr. Kate Scharer, an assistant professor in Appalachian’s Department of Geology and one of the organizers of the event.
“Geologists know the factors that make land sliding more likely, so interacting with the National Weather Service about the timing of the weather data they collect and learning about their warning systems is an important first step towards translating geologic knowledge into other hazard warnings associated with storms,” she said.
“There is so much we can do together to help with community preparedness, communication and community action,” said Steve Keighton from the NWS’s Blacksburg office. “Our goal is to do the best we can to protect life and property, and the more quality data we have to do that the better.”
Forecasting a snowstorm or rain event is fairly easy, thanks to the tools of satellite imagery, computer modeling and radar. Factors leading to a specific landslide or slope movement aren’t as easy to determine. Meteorologists, geologists and emergency management each have a piece of the puzzle toward achieving the goal of forecasting landslides and responding to such events..
Among the tools for anticipating landslides are landslide hazard maps being created by the N.C. Geological Survey in NCDENR. That project began in 2006 as part of the state’s Hurricane Recovery Act following landslides and increased slope movement occurring in western North Carolina after Hurricanes Frances and Ivan in 2004.
Nineteen counties were identified for mapping, the first of which were Macon, Watauga, Buncombe and Henderson counties. Those four counties represent 41 percent of the population in the Hurricane Recovery Act counties based on the 2000 census data, according to N.C. Geological Survey senior geologist Rick Wooten. The maps are online at www.geology.enr.state.nc.us/Landslide_Info/Landslides_main.htm.
According to data compiled by NCDENR geologists, intense rainfall from the remnants of Hurricanes Frances and Ivan in 2004 triggered at least 400 landslides that caused five deaths, destroyed 27 homes and disrupted transportation throughout western North Carolina. A damaging landslide occurs nearly every year in the region, and landslides usually happen in the same general areas as past landslides.
Of the counties mapped to date, Watauga County had the most landslide activity, with more than 2,250 landslides of varying intensity identified, the majority of which were triggered by an August 1940 storm that killed 14 people and destroyed or damaged at least 32 structures. A landslide following Hurricane Frances in 2004 destroyed one home and resulted in eight others being condemned in the White Laurel housing community.
More than 1,200 landslide features (landslides and landslide deposits) have been identified in Buncombe County, 165 landslides were identified and mapped in Macon County, and 88 landslide locations identified in Henderson County.
“It’s important for geoscientists to record the impacts from these record storms,” said Francis Ashland with the USGS in Virginia. “These storms are important case histories for understanding what can happen in this region.”
While the regional offices of the National Weather Service issue outlooks, watches and warnings for flash floods, currently there is no specific protocol for issuing statements regarding potential debris flows, or landslides, associated with heavy rains. A better understanding the geology of landslides and communication between geologists and meteorologists will help the National Weather Service develop these protocols. Feedback from regional emergency management personnel helps the National Weather Service refine the language in the hazard warning.
Scharer, whose research focuses on the geology of earthquakes, said the workshop provided a better understanding of the different terminology used by geologists and meteorologists.
“Physical scientists like geologists and meteorologists always need to consider ways to communicate their data more clearly with the end users,” Scharer said. “It’s easy to communicate scientific data within your own discipline, but it becomes critical to be able to use a common vocabulary across disciplines and in potentially dangerous situations like these. Earthquakes and landslides are similar in that they have a low probability of occurrence on any day, but the effects can be devastating.”
Scharer said the next step will be to generate different types of warnings that might be issued during landslide threats and determine how that information will be shared with emergency response agencies and the public