Geology and Geohazards in Western North Carolina

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1 Geology and Geohazards in Western North Carolina Rick Wooten Jennifer Bauer Stephen Fuemmeler Tommy Douglas Anne Witt Ken Gillon Rebecca Latham North Carolina Geological Survey

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3 North Carolina Geological Survey Map and describe geology and mineral resources of the State. Encourage wise conservation and use of our geologic resources. Provide accurate, unbiased information for societal needs. Dennison Olmstead

4 Buncombe County Watauga County Sulfidic Rock Asheville Macon County

5 Geologic Provinces in North Carolina

6 Asheville Tectonic Elements of the Southern Appalachians Hatcher, Merschat and Thigpen (2005)

7 Bedrock Geologic Map of Buncombe County Sulfidic-Graphitic Rock Landslides

8 ~65 M Present Mountains Rejuvenate Isostatic Uplift Weathering Debris Fan Deposition ~220 Ma Laurentia -Gondwana Split - Rift Basins Form to East - Extensional -Transtensional Faulting and Fracturing ~ Alleghenian Orogeny Thrust Faulting Folding Ductile Brittle Transition ~ Acadian Neo-Acadian Orogeny Deformation - Metamorphism Granitoid Intrusion ~460 Ma Taconic Orogeny Begins Folding Thrust Faulting Intrusion Metamorphism ~600 Ma Rifting Deposition Laurentia Forms ~1 Ga Grenville Orogeny Rodinia Forms

9 Asheville Basin Blue Ridge Escarpment Brevard Fault Zone Asheville Basin 6m LiDAR DEM Hillshade

10 Devonian Granodiorite and Pegmatite Spruce Pine Mining District Ultra-High Purity Quartz

11 approx. scale 50cm gneissic layering F2(?) fold axis F3(?) fold axes pegmatite and quartz intrusions fractures weathering

12 Earthquakes New Madrid Seismic Zone Eastern Tennessee Seismic Zone Charleston Seismic Zone

13 Modified from Stover and Coffman, 1993 Earthquakes

14 Magnitude: 3.7 Location: 5 mi west of Hot Springs Date: August 24, :09:41 EDT Intensity: IV Slight Damage (?) Depth: 5.0 km Felt: AL, GA, KY, NC, SC,TN Source: USGS National Earthquake Information Center

15 Recent rockslide in Haywood County

16 Tropical Storm Rockslides Cindy July 6-7, 2005

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18 Rebecca Latham Wed. 10:45 A.M. Session 17 Thurs. Field Trip Sulfidic Bedrock August 18, 2006 Rockslide Blue Ridge Parkway

19 NNP values for rock in previous slide.

20 Fe Oxide Staining Typical on Sulfidic Bedrock Bryson City Swain County 5 mi

21 Big Slow Movers Landslides in Weathered Rock Toxaway River Slide Gorges State Park

22 x Embankment Failure Debris Slide-Flow

23 Debris Flow Debris Fan Debris Fan Deposits Areas of Past Debris Flow Activity

24 Recurring Weather Patterns Landslide Triggering Storms in Western North Carolina

25 July 15-16, 1916 French Broad Watershed Transylvania, Buncombe, Henderson, McDowell Counties Flooding and Landslide Fatalities

26 Approximately 5,376,548,571 gallons of water changed hands. Max. Outflow ~ 55 mph ~293,000 cfs 6.9 mi - N.C. / S.C. Line Lake Toxaway Dam Failure and Debris Flow Aug. 13, 1916

27 August 13-14, 1940 Watauga County 2,099 Landslides 14 Landslide Fatalities 32 Structures destroyed U.S. 421 severed in 21 places 260 Slides impacted roads

28 August 28-31, 1940 Tuckasegee Pigeon River Watersheds Jackson Haywood Counties 200+ Landslides 6 Landslide Fatalities Sylva Herald Photo Lynn Hotaling

29 Ivan Hurricanes Frances & Ivan September 2004 ~400 Landslides 5 Fatalities NOAA 27 Homes Destroyed or Condemned

30 Peeks Creek Debris Flow Macon County Sept. 16, 2004 Hurricane Ivan 5 Fatalities 16 Homes Destroyed Track Length: 2.25 miles Max. Velocity: ~33 mph Max. Discharge: ~70,000 cfs

31 Damage and Deposits Peeks Creek Debris Flow

32 Peeks Creek Debris Flow Initiation Zone Fishhawk Mountain

33 Fishhawk Mtn. Possible location of June 15, 1876 debris flow on Fishhawk Mtn. described by T.L Clingman in 1877 T.L. Clingman Sept. 16, 2004 Deposit Younger Debris Flow Deposit ( ) 14 C Pre-2004 Debris Flow Deposits in Peeks Creek Older Debris Flow Deposit (~23,260) 14 C

34 Watauga County Boone Slope Movements Slope Movement Deposits Statewide Database Statistical Information NCGS Landslide Hazard Mapping GIS PRODUCTS Geologic Hazards Acid-Producing Rock Potentially Unstable Rock Slopes Stability Index Debris Flow Susceptibility Debris Flow Pathways

35 Buncombe County Asheville I - 40 Debris Fan Deposits Slope Movements and Slope Movement Deposits Map

36 421 BRP 1940 Guy Carlton Debris Flow Then and Now - Watauga County

37 Wayah Debris Flow - Hurricane Ivan September 16, 2004 Macon County 5=2004 debris; 1-4=pre-2004 debris flow deposits; CDSR=saprolite old fan deposit 2004 deposit U.S.F.S. Photo

38 Landforms and Orographic Rainfall Enhancement Macon County Nantahala Mountains Escarpment Frances Ivan

39 Stability Index Map (SINMAP*) Where Debris Flows are Likely to Start Map Color Code Predicted Stability Zone Relative Debris/Earth Flow/Slide Hazard Ranking 1 Stability Index Range 2 Factor of Safety (FS) 3 Probability of Instability 4 Predicted Stability With Parameter Ranges Used in Analysis Possible Influence of Stabilizing or Destabilizing Factors 5 Unstable 0 Maximum FS <1 100% Upper Threshold of Instability High >50% of FS <1 >50% Range cannot model stability Optimistic half of range required for stability Stabilizing factors required for stability Stabilizing factors may be responsible for stability Lower Threshold of Instability Moderate >50% of FS >1 <50% Pessimistic half of range required for instability Destabilizing factors are not required for stability Nominally Stable Minimum FS = 1 Moderately Stable Low Minimum FS = 1.25 Cannot model instability with most conservative parameters specified Cannot model instability with most conservative parameters specified Minor Destabilizing destabilizing factors factors not could required lead for to instability Moderate destabilizing factors are required for instability Stable >1.5 Minimum FS = 1.5 Debris Flow and Debris Slides Unmodified ( natural or unaltered) slopes > 5 inches /24 hours Rainfall Cannot model instability with most conservative parameters specified Significant destabilizing factors are required for instability *Pack and others, 1998

40 Track Initiation Zone Cross section showing bedrock structural control on catchment geometry in debris flow initiation zone. Stability Index Map Wayah Debris Flow Area Macon County

41 Macon County Lineaments, Landslides, & Structural Fabrics

42 Debris Flow Pathways Map Asheville Rocky Branch Bent Creek 1977 Debris Flows

43 Mapped debris flow pathways Potential debris flow pathways (using Arc Hydro) Past debris flow activity (deposits) No known past or potential debris flow activity increasing Relative Hazard decreasing Debris Flow Pathways Map

44 increasing Relative Hazard Younger Debris Flow Deposits in Drainages decreasing Older Debris Fan Deposits on Upland Surfaces of Drainage Divides

45 Bedrock Geologic Compilation Map of of Watauga County Zone of Potential Rock Slope Instability L F S Z LFSZ = Linville Falls Shear Zone

46 sliding surface = completely decomposed brecciated mylonite release surfaces = fractures Brittle Overprint on Ductile Deformation Fabrics

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48 Landslide Hazards Web Map Viewer -Watauga County

49 QUESTIONS? North Carolina Geological Survey Mountains (Asheville) Raleigh Office Raleigh Field Office (Piedmont and Coastal Plain)