geology and geohazards in western north carolina

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)

Rick.Wooten@ncdenr.gov

919-733-2433 –Raleigh Office

919-733-7353 – Raleigh Field Office (Piedmont and Coastal Plain)