By Jamie Kritzer, DENR
The folks in the N.C. Geological Survey have recently created the first in a series of county maps that will enable communities to evaluate and reduce the risks of building homes and other structures in landslide-prone areas of the North Carolina mountains.
Officials with the Geological Survey, a section of the Division of Land Resources, say the first series of three maps were developed for Macon County. The maps depict landslide-prone areas and provide developers, county officials and residents with information that can be used to determine where to safely construct homes, roads and other structures.
State geologists plan to develop landslide maps for five other mountain counties during the next two years.
The idea to create such maps is meant to help prevent the destruction from landslides like the one in September 2004 that killed five people and destroyed 16 homes in the Peeks Creek community of Macon County. That landslide carried massive amounts of debris more than two miles and was triggered by heavy rainfall from remnants of Hurricanes Frances and Ivan. Those storms also started more than 140 other landslides throughout western North Carolina. Back-to-back storms similar to Frances and Ivan caused extensive flooding and fatal landslides in western North Carolina in 1916 and 1940, too. Geologists say it is very likely this dangerous weather pattern will occur again in North Carolina.
“There have been landslides in the North Carolina mountains since prehistoric times,” said Tyler Clark, chief geologist with the N.C. Geological Survey. “But now more people are vulnerable because more people are choosing to live in areas that may be prone to landslides. When you add to that hurricanes or other storms that could start a landslide, you can have a really dangerous situation.”
The three-year Landslide Hazard Mapping Program was funded with $1.3 million from the Hurricane Recovery Act of 2005. In February 2005, Gov. Mike Easley signed the Hurricane Recovery Act to provide disaster assistance to people, businesses and public agencies that sustained damage from one or more of the six hurricanes that struck North Carolina in 2004.
Funds from the Hurricane Recovery Act pay for the work of six geologists headquartered in Asheville with the N.C. Geological Survey, which is a section of the N.C. Department of Environment and Natural Resources.
The geologists mapped the locations of both recent and old landslides recognized by deposits of rock, sand and clay. To make fieldwork more efficient, geologists used several state-of-the art technologies, including topographic data from a system called Light Detecting and Ranging, or LiDAR. They also used existing soil and geologic maps, computer modeling, satellite and aerial photography and data from geographic information systems and global positioning system.
The three Macon County maps, when used together, show where landslides have occurred, where they might start and where they might go once they start.
“Our studies of landslides across North Carolina over the last year and a half indicate that a large number of them occurred because of things that people have done to alter the landscape,” Clark said. “These activities have included construction of roads, house building and the cutting of trees. When you try to develop land on a steep slope, you can change a stable condition to an unstable one.”
Research conducted during the project revealed that about 56 percent of all landslides in Macon County happened on slopes that had been altered in some way by people, Clark said.
“You can build in many places in North Carolina,” Clark said. “But you have to do it right. You need to have good planning, design and construction anytime you develop, and part of that is knowing what hazards to look for.”
Clark expects that landslide hazard maps will be available to the public for Buncombe and Watauga counties by next summer. Maps for Haywood, Henderson and Jackson counties are expected to be available in 2008, Clark said.
Staff with the N.C. Geological Survey also are compiling a database of modern and prehistoric landslides for western North Carolina. So far, geologists have put together a list of more than 2,000 landslides in mountain and Piedmont counties.
Geologists are providing their data to county officials, planners, developers, residents and people who work with emergency management agencies. As a part of their work, the scientists recently designed a publication called “When the Ground Moves: A Citizen’s Guide To Geologic Hazards in North Carolina.” The 23-page booklet provides information about landslides, abandoned mines, sinkholes, flooding and other geologic hazards. The booklet is $5.
For copies of the Macon County map series or the booklet, call the N.C. Geological Survey sales office at
(919) 715-9718. The Macon County map series is $28. Maps are available at the N.C. Geological Survey sales office in the Archdale Building of Raleigh.
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