Geologic hazards in North Carolina — Landslides

This section provides examples about effects of Hurricanes Frances and Ivan in September 2004 in western North Carolina.

Landslide contents

The landslide section consists of several pages to facilitate on-line user viewing. This page is the fourth of five that are based on a recent staff geologist presentations at numerous public meetings. The pages are:

Landslide presentation

The following images were included in a MS PowerPoint presentation used by North Carolina Geological Survey geologists from the Swananoa office at many public landslide outreach meetings. The presentation has been adapted to the Internet for broader distribution. This page is on "Hurricanes Frances and Ivan -- September 2004." Links to other topics appear in the contents shown above.

Slide numbers correspond to those of the original MS PowerPoint presentation. Slide numbers "missing" are slides that were turned into text. Captions are from the original presentation.

Slide 60 - Rainfall from the remnants of Hurricanes Frances and Ivan caused flooding and triggered numerous landslides in western North Carolina. National Weather Service rainfall maps showing precipitation from the remnants of Hurricanes Frances (upper left) and Ivan (bottom right). Inaccuracies in the maps may be due to the widely spaced rain gage network in western N.C.

 

Slide 61 - Home destroyed by a debris slide-flow triggered by heavy rain during Hurricane Frances. It does not require a large landslide to cause considerable damage. This embankment failure that mobilized into a debris flow is only about 125 feet long.

 

Slide 62 - Plan view map of White Laurel subdivision showing debris flows (embankment failures) outlined in red. House on lot 547 (shown in blue) was destroyed; Red lot numbers indicate condemned homes; purple hachured lines indicate scarps; green lot numbers indicate homes with foundation cracks. Photographs show scarps and damage from embankment failures. The slope failures here appear to be related to cut-and-fill type construction on steep slopes.

 

Slide 63 - Home destroyed by embankment failure/debris flow. The occupant managed to leave the house after it was destroyed by the debris flow, but spent the night outside during the storm.

 

Slide 64 - Jonas Ridge Burke County. Left: View looking downslope from failed embankment (driveway) toward destroyed house. Top Right: Multiple soil and gravel layers, and a buried asphalt layer in embankment indicate the area may have been subsiding before the failure. Bottom Right: Scarp in yard encroaching upon house visible in photo top right.

 

Slide 65 - Color infrared aerial photograph showing the location of the Bear Rock Estates debris flow track in red. This slope failure occurred during Hurricane Frances.

 

Slide 66 - Left: View looking down the track of the Bear Rock debris flow. Right: Initiation zone of debris flow where the subdivision road crosses a drainage. Unstable slope remains at the head of the debris flow. Multiple generations of cracks in the pavement indicates road subsidence at this location prior to the debris flow.

 

Slide 67 - Geologic cross-section showing geologic conditions in the debris flow initiation zone. The road failed in a similar manner at this location about 20 years ago.

 

Slide 68 - Debris flow scarps encroaching on a home in McDowell County. Deep soil characteristic of weathered carbonate rock of the Shady Dolomite is exposed in the scarps. Failure occurred during Hurricane Frances.

 

Slide 69 - Honeycutt Mountain Right: Arrow shows location of home in previous slide built on steep slopes above an abandoned quarry in the Shady Dolomite. Left: May 10, 1954 aerial photograph of area. Approximate location of the home in photo right indicated by yellow square; red dashed line outlines past landslide deposits in the quarry.

 

Slide 70 - Honeycutt Mountain. Excerpt of 1985 geologic map showing the location of the house in previous slide (yellow arrow pointing to yellow dot). The Shady Dolomite, labeled Cs on the map is of limited extent in N.C.

 

Slide 71 - Honeycutt Mountain. Left: Schematic cross section showing slope failures in the deep, clayey soil overlying an highly irregular weathering surface on the Shady Dolomite. Right: Leaning tree on the steep slopes below the house indicate unstable slopes prior to the damaging slope failure during Hurricane Frances.

 

Slide 72 - Catatoga Embankment Failure. Map showing location of embankment failure that mobilized into a debris flow. Failure occurred during Hurricane Frances.

 

Slide 73 - Catatoga Embankment Failure. View looking upslope at the initiation zone of the embankment that failed. Seepage along a steeply sloping bedrock surface can be seen in both scars.

 

Slide 74 - Debris dam in Indian Creek formed by the Catatoga embankment failure-debris flow.

 

Slide 75 - Blue Ridge Parkway. Failure occurred during Hurricane Frances. Left and Right: Aerial photographs of the Bear Drive Branch Creek embankment failure-debris flow originating along the Blue Ridge Parkway between Mt. Mitchell and Linville. Slope stability problems may not show up until many years after construction. Bottom Center: Debris flow damage to U.S. Forest Service road and bridge along Bear Drive Branch.

 

Slide 76 - Photographs of ancient and modern debris flow deposits below the Blue Ridge Parkway near Curtis Creek, Pisgah National Forest, McDowell County. Top Center: An embankment failure on the Blue Ridge Parkway during Hurricane Frances mobilized into a debris flow and deposited boulders and large woody debris near Curtis Creek. Bottom Left: Imbricated boulders deposited by a Hurricane Frances debris flow (embankment failure) along the Blue Ridge Parkway. Bottom Right: Ancient debris flow deposit with imbricated boulders in the same stream channel as shown in bottom left photo.

 

Slide 77 - Map showing track (red) of the Little Pine Debris Flow in Madison County. The slope failure occurred during Hurricane Ivan.

 

Slide 78 - Little Pine Debris Flow. A. Apparent initiation zone (road embankment) of Little Pine Debris Flow triggered by Hurricane Ivan. B. View down track scoured by debris flow. C. Barn destroyed by debris flow, out of view is a cabin damaged by the debris flow. Red arrow points to person for scale.

 

Slide 79 - Hebo Mountain. Failure occurred during Hurricane Ivan. Left: Embankment failure that mobilized into a debris flow. Rock baskets installed to reinforce the embankment appear to have been placed on unstable foundation material. Right: Scarp (indicated by red arrow) developing behind the main scarp and near the house.

 

Slide 80 - Starnes Cove Debris Flows. Coalescing debris flow tracks shown in red. Failures occurred during Hurricane Ivan.

 

Slide 81 - Starnes Cove Debris Flows. Right: View looking up debris flow tracks toward logging road where the debris flows appear to have originated. Left: View looking down debris flow track, red arrow points to mud line in tree about 25 feet above base of tree, and at least 30 feet above stream channel; 56 geologist at base of tree for scale.

 

Slide 82 - House destroyed by the Starnes Cove debris flow. Resident was in the house at the time and survived. The debris flow also destroyed the garage of the house immediately downstream.

 

Slide 83 - Home site embankment failure in the Peaks at Lake Lure that mobilized into a debris flow during Hurricane Ivan. Left: View looking upslope along track to initiation zone (red arrow). Right: Logs and other woody debris within embankments do not contribute to the long term stability of the embankment.

 

Slide 84 - Upper track of Wayah debris flow 1 west of Franklin in Macon County. This debris flow appears to have initiated from naturally occurring conditions on a steep hillslope. Failure occurred during Hurricane Ivan.

 

Slide 85 - Lower track and deposit of Wayah Debris Flow 1. The debris flow destroyed a barn that was located in front of the house. The mud from the most recent debris flow was deposited onto the floodplain of Wayah Creek.

 

Slide 86 - Deposits from multiple ancient debris flow and flood deposits are exposed in the recently eroded channel of Wayah Debris Flow 1. Deposit 4 indicates large woody debris piled behind the tree from the recent (Ivan) debris flow.

 

Slide 87 - View of the Hurricane Ivan debris flow track of Wayah Debris Flow 1 incised through prehistoric (?) debris flow deposits forming a debris fan (top of fan indicated by red dashed line) at the stream outlet.

 

For additional information

The contact for additional information about geologic hazards in North Carolina is Mr. Richard Wooten, P.G.; his e-mail is Rick.Wooten@ncmail.net. He is located in the Swannanoa, North Carolina office (western North Carolina) and can be reached by telephone at 828.296.4500. His mailing address is: 2090 U. S. Highway 70, Swannanoa, North Carolina 28778. An alternate North Carolina Survey staff geologist contact is Dr. Jeff Reid, P.G., 512 North Salisbury Street, Raleigh, North Carolina, 27699-1612. His telephone number is 919.733.2423 x403. His e-mail is Jeff.Reid@ncmail.net.