geology and geohazards in western north carolina
TRANSCRIPT
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
North Carolina Geological Survey
• Map and describe geology and mineral resources of the State.
Dennison Olmstead - 1825
• Encourage wise conservation and use of our geologic resources.
• Provide accurate, unbiased information for societal needs.
Sulfidic RockWatauga County
Macon County
Buncombe County
Asheville
Geologic Provinces in North Carolina
Tectonic Elements of the
Southern Appalachians
Hatcher, Merschat and Thigpen (2005)
Asheville
Bedrock Geologic Map of Buncombe County
Sulfidic-Graphitic Rock Landslides
~460 Ma Taconic Orogeny Begins Folding – Thrust Faulting – Intrusion – Metamorphism
~390-330 Acadian – Neo-Acadian Orogeny Deformation - Metamorphism – Granitoid Intrusion
~320-260 Alleghenian Orogeny Thrust Faulting – Folding Ductile–Brittle Transition
~220 Ma Laurentia -Gondwana Split - Rift Basins Form to East - Extensional -Transtensional Faulting and Fracturing
~600 Ma Rifting – Deposition – Laurentia Forms
~1 Ga Grenville Orogeny – Rodinia Forms
~65 M–Present Mountains Rejuvenate Isostatic Uplift Weathering – Debris Fan Deposition
Blue Ridge Escarpment
Brevard
Fault
ZoneAsheville BasinAsheville Basin
6m LiDAR6m LiDAR
DEM HillshadeDEM Hillshade
Asheville Basin
Devonian Granodiorite
and Pegmatite
Spruce Pine Mining District
Ultra-High Purity Quartz
approx. scale
50cm
gneissic layering F2(?) fold axis F3(?) fold axes pegmatite and quartz intrusions fractures weathering
Earthquakes
Charleston Seismic Zone
Eastern Tennessee
Seismic Zone
New Madrid Seismic Zone
Earthquakes
Modified from Stover and Coffman, 1993
Magnitude: 3.7 Location: 5 mi west of Hot SpringsDate: August 24, 2005 11:09:41 EDT Intensity: IV – Slight Damage (?)Depth: 5.0 kmFelt: AL, GA, KY, NC, SC ,TN
Source: USGS National Earthquake Information Center http://neic.usgs.gov
Recent rockslide in Haywood County
RockslidesTropical Storm Cindy
July 6-7, 2005
Sulfidic BedrockAugust 18, 2006 Rockslide
Blue Ridge Parkway
Rebecca Latham
Wed. 10:45 A.M.
Session 17
Thurs. Field Trip
NNP values for rock in
previous slide.
5 mi
Bryson City Swain County
Fe Oxide Staining Typical on
Sulfidic Bedrock
Landslides in Weathered Rock
Toxaway River Slide
Gorges State Park
Big Slow Movers
Embankment Failure
Debris Slide-Flow x
Debris Flow – Debris Fan
Debris Fan Deposits
Areas of Past Debris Flow Activity
Recurring Weather Patterns
Landslide Triggering Storms in Western North Carolina
July 15-16, 1916French Broad WatershedTransylvania, Buncombe,
Henderson, McDowell CountiesFlooding and Landslide Fatalities
6.9 mi - N.C. / S.C. Line
Lake ToxawayDam Failure and Debris
Flow Aug. 13, 1916
“Approximately 5,376,548,571 gallons of water changed hands.”
Max. Outflow ~ 55 mph ~293,000 cfs
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
Sylva Herald Photo – Lynn Hotaling
August 28-31, 1940Tuckasegee – Pigeon River
Watersheds Jackson – Haywood Counties
200+ Landslides
6 Landslide Fatalities
• ~400 Landslides
• 5 Fatalities
• 27 Homes Destroyed or Condemned
Hurricanes Frances & IvanSeptember 2004
IvanIvan
NOAA
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
Damage and Deposits Peeks Creek Debris Flow
Peeks Creek Debris Flow
Initiation Zone
Fishhawk Mountain
Fishhawk Mtn.
T.L. Clingman
Sept. 16, 2004 Deposit
Younger Debris Flow Deposit (370-390) 14C
Older Debris Flow Deposit (~23,260) 14C
Pre-2004 Debris Flow Deposits in Peeks
Creek
Possible location of June 15, 1876 debris
flow on FishhawkMtn. described by
T.L Clingman in 1877
Stability Index Debris Flow Susceptibility Debris Flow Pathways
Statewide Database Statistical Information
Geologic Hazards Acid-Producing RockPotentially Unstable
Rock Slopes
Slope Movements – Slope Movement Deposits
Watauga County
NCGS Landslide Hazard Mapping GIS PRODUCTS
BooneBoone
Slope Movements and
Slope Movement Deposits Map
Asheville
Debris Fan
Deposits
I I -- 4040
Buncombe County
421BRP
2007
19401940
1940 Guy Carlton Debris Flow Then and Now - Watauga County
2007
2004 deposit
deposit
U.S.F.S. Photo
old fan
Wayah Debris Flow - Hurricane Ivan September 16, 2004 Macon County
5=2004 debris; 1-4=pre-2004 debris flow deposits; CDSR=saprolite
Landforms and Orographic Rainfall Enhancement
Macon CountyNantahala Mountains Escarpment
FrancesIvan
Stability Index Map (SINMAP*) Where Debris Flows are Likely to Start
Map Color Code
Predicted Stability Zone
Relative Debris/Earth Flow/Slide Hazard
Ranking 1Stability Index
Range2Factor of Safety
(FS) 3Probability 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% Range cannot model stability
Stabilizing factors required for stability
Upper Threshold of Instability 0 - 0.5 >50% of FS <1 >50% Optimistic half of range
required for stabilityStabilizing factors may be responsible for stability
Lower Threshold of Instability Moderate 0.5 - 1 >50% of FS >1 <50% Pessimistic half of range
required for instabilityDestabilizing factors are not required for stability
Nominally Stable 1 - 1.25 Minimum FS = 1 ___Cannot model instability with most conservative parameters specified
Minor destabilizing factors could lead to instability
Moderately Stable 1.25 - 1.5 Minimum FS = 1.25 ___Cannot model instability with most conservative parameters specified
Moderate destabilizing factors are required for instability
Stable >1.5 Minimum FS = 1.5 ___Cannot model instability with most conservative parameters specified
Significant destabilizing factors are required for instability
Low
High
Destabilizing factors not required for instability
• Debris Flow and Debris Slides
• Unmodified (“natural” or unaltered) slopes
• > 5 inches /24 hours Rainfall
*Pack and others, 1998
Initiation Zone
Stability Index Map Wayah Debris Flow Area
Macon County
Cross section showing bedrock structural control on catchment geometry in debris flow initiation zone.
Track
Macon County Lineaments, Landslides, & Structural Fabrics
Debris Flow
Pathways Map
Asheville
Rocky Branch Bent Creek
1977 Debris Flows
Mapped debris flow pathways
Potential debris flow pathways (using Arc Hydro)
Past debris flow activity (deposits)
No known past or potential debris flow activity
Relative Hazard
increasing
decreasing
Debris Flow Pathways Map
increasing
decreasing
Younger Debris Flow Deposits in Drainages
Older Debris Fan Deposits on Upland Surfaces of Drainage Divides
Relative Hazard
Bedrock Geologic Compilation Map of
Watauga County
Bedrock Geologic Compilation Map of
Watauga County
Zone of Potential Rock Slope Instability
L F S Z
LFSZ = Linville
Falls Shear Zone
Brittle Overprint on
Ductile Deformation
Fabrics
sliding surface = completely decomposed brecciated mylonite
release surfaces = fractures
Landslide Hazards Web Map Viewer -Watauga County
http://wfs.enr.state.nc.us/fist/
QUESTIONS ?
North Carolina Geological Surveyhttp://www.geology.enr.state.nc.us
828-296-4500 – Mountains (Asheville)
919-733-2433 –Raleigh Office
919-733-7353 – Raleigh Field Office (Piedmont and Coastal Plain)