The laws of physics don’t stop at state boundaries: Challenges and accomplishments in documenting landslide activity in the Central and Southern Appalachians Witt, Anne C.1 and Wooten, Richard M.2

(1) Virginia Department of Mines, Minerals and Energy, Division of Geology and Mineral Resources, Charlottesville, VA; anne.witt@dmme.virginia.gov (2) North Carolina Geological Survey, Swannanoa, NC; Rick.Wooten@ncdenr.gov

ABSTRACT: Landslides, particularly debris flows and rockslides, are a recurring hazard in high-relief areas of the Blue Ridge and Valley and Ridge provinces of Virginia, and the Blue Ridge and adjacent Piedmont of North Carolina. Although neither state currently funds the mapping of various landslide hazards, the Virginia Division of Geology and Mineral Resources (VA DGMR) and North Carolina Geological Survey (NCGS) still actively report on landslide incidence and respond to landslide events when there is a threat to life or property. Virginia piloted a landslide hazard mapping project in Page County, Virginia in 2012 funded by a grant from the Federal Emergency Management Agency. A portion of these funds were used to establish a statewide GIS-based Virginia landslide database, structured to match a database originally developed by the NCGS from 2005-2011. Initial landslide location information has been compiled from aerial photography, digital elevation data, pre-existing geologic mapping, and various historical sources. Field mapping has added additional information about the geology, geomorphology, soil characteristics, and vegetation type at individual landslide sites. This information is stored in an ESRI ArcGIS geodatabase with similar attribute entries and fields, creating a paired dataset that is updated independently by each agency, but retaining the consistency of the input data. The NCGS geodatabase currently has over 3,400 landslide point locations and 3,200 landslide deposit polygons, primarily identified during landslide hazard mapping completed in four North Carolina counties. The VA DGMR geodatabase currently has over 5,200 landslide points and associated data. A majority of the features identified by the VA DGMR and the NCGS are debris slides and debris flows associated with known historic flood events that occurred between 1916 and 2013. At present, updates to the VA DGMR and NCGS geodatabases are made in conjunction with responses to requests for technical assistance during landslide events or by customer request. Our intent is to use these paired datasets for further statistical analysis to help quantify the frequency and severity of landslide events on the broader scale of the central Appalachians. Additionally, these datasets are useful tools for emergency management and regional planners as they update hazard mitigation plans and other ordinances, and serve to inform citizens of landslide hazards in their area.

Improving Field Mapping Efficiency VA DGMR is currently beta-testing the ESRI application ArcGIS Collector for data collection in the field. Results are generally positive. The application allows for the transfer of the original landslide geodatabase schema and pull-down menus onto the internet for use on a handheld device. Currently, there is no functionality for related tables and field note collection has been streamlined.

Known landslide locations in North Carolina and Virginia (as of Jan 2015). Most landslides occur in the steep areas of the Blue Ridge and Valley and Ridge, although a few also occur further east in the Piedmont and Coastal Plain.

REFERENCES: Carter, M.W., Berquist, C.R.(2005) A preliminary investigation of the Chimborazo Hill landslide of August 30, 2004. Virginia Minerals Vol 8, No 4, 25-36 p.

Witt, A.C., Heller, M.J. (2014) Landslide hazard mapping in Page County, Virginia: Processes, results and lessons learned. In: Abstracts with Programs, Geol Soc Am 46:23, Blacksburg, VA.

Wooten, R.M., Witt, A.C., Miniat, C.F., Hales, T.C., Aldred, J.L. (2015) Frequency and magnitude of selected historical landslide events in the Southern Appalachian Highlands of North Carolina and Virginia: Relationships to rainfall, geological and ecohydrological controls, and effects. In: Greenberg, C.H., Collins, B.S. (eds) Natural disturbances and range of variation: Type, frequency, severity, and post-disturbance structure in Central Hardwood Forests. Springer, New York (in press).

Feature Classes

Data Tables

Pull-down menus

Data is related between feature classes and data tables using a unique ID number. For example, a geologist takes a GPS location at a landslide headscarp (process point). Any field pictures are entered into the picture data table. A landslide track is drawn from aerial photography. All of that data is related together using the same unique ID.

Paired Statewide Geodatabases In North Carolina and Virginia, earlier landslide mapping (primarily paper mapping and data compiled in Microsoft Excel/Access) has been integrated into similar ArcGIS geodatabases for ease of data entry and future statistical analyses. This geodatabase design was originally developed by the NCGS between 2005-2011, and was adopted by DGMR with minimal changes. Several entries are preloaded into pull-down menus for content data collection in the field and the office. Currently, the NCGS and DGMR do not actively map landslides and landslide deposits, but landslide features are added to the geodatabases on an as needed basis.

Primary Feature Classes (points, lines and polygons) Landslide Processes (points)

Field Notes (points) – vary slightly between VA/NC

Group Ruptures (lines) – scarps and tension cracks

Landslide Tracks (polygons)

Landslide Deposits (polygons)

Non-spatial tables (Data Tables)

Rock Table – rock type/minerals

Structure Table – geological structure data and measurements

Soil Table – soil type and properties

Soil Test Table – holds info about soil testing at a location

Picture Table – photos taken in the field

All related to each other via

Feature ID/ Point ID

Intense rainfall occurring over a short time period (>125-250 mm in 24 hrs) is the primary trigger for debris flows in the Central Appalachians. From 1916-2006 seven major cyclonic storms have tracked over the area producing hundreds to thousands of landslides. Table showing major rainfall events/amounts

and the number of landslides reported in NC and VA (modified from Wooten et al, 2015).

A Shared Storm History

Common Landslide Processes Although many types of landslides occur in VA and NC, the debris flow is the dominant and most destructive landslide process. Rockslides and falls also occur in the crystalline metamorphic rocks of the Blue Ridge, often failing along intersecting bedrock discontinuities and areas of differential weathering.

Major Study Areas in Virginia The DGMR geodatabase currently has >5,200 landslide points, primarily associated with Hurricane Camille in 1969 (3,700+). Previous mapping by the USGS and DGMR was digitized into the database, while new mapping has taken place in Page County, VA (2013).

B1 B2

B. Headscarp (B1) and bouldery debris behind tree (B2) within a debris flow track mapped as part of a 2013 FEMA funded landslide hazard study in Page County, VA (Witt and Heller, 2013).

C. Debris flow boulders and destroyed house associated with Hurricane Camille (1969) in Nelson County, VA (DGMR photo archive).

C

A. Large, 11-acre debris slide mapped in Richmond, VA after Hurricane Gaston in 2004 (Carter and Berquist, 2005).

D

D. Debris flow along U.S. 421 in Watauga County, NC associated with an August 1940 storm.

E E. A debris flow that initiated from a failed retaining wall on the property of the Ghost Town in the Sky amusement park in Maggie Valley, NC.

F. Massive imbricated boulders along Peeks Creek in Macon County, NC. This 1.5 km-long debris flow occurred during Hurricane Ivan in 2004.

F

Major Study Areas in North Carolina The NCGS geodatabase currently has >3,400 landslide points and >3,200 landslide deposit polygons. Data is primarily concentrated in the four counties with completed landslide hazard maps and along the NC segment of the Blue Ridge Parkway (assessment completed in 2008).

Common Landslide Deposits The present Appalachian landscape includes many remnants of prehistoric (Pleistocene and older) debris flow deposits. These features are typically composite, recording multiple episodes of prehistoric and historic mass wasting in mountain coves and foot slopes.

Talus Slope Page County, VA

Boulder Stream Page County, VA

Composite debris deposit in Buncombe County, NC mapped on a

6-meter LIDAR base

Data is collected and edited using an iPhone 5.

Data is first transferred and shared on the ArcGIS Online website. This allows multiple users to view and edit the data in the office and the field simultaneously.

• Eliminates the need for field camera, but requires special case

• Can take geologic measurements using the phone (maybe)

• Data is updated to the web automatically reducing the potential for data loss

• Requires careful monitoring of battery life

• Lots of useful preloaded maps through ESRI

Landslide debris deposit associated with Hurricane Camille (1969) in Nelson County, VA.

Conclusions Accomplishments: • We have a functional, adaptable geodatabase that works for our needs. The basic

schema can be shared with another state with only minor modifications.

• Together VA and NC have produced 5 county-wide landslide hazard studies and a number of local case studies. This has greatly broadened our understanding of landslide processes as well as the triggering mechanisms which cause them in the Central Appalachians.

• We have a workflow that is efficient and minimizes time in the office. ArcGIS Collector may improve that efficiency even more.

Challenges: • Funding Sources – Neither state actively funds landslide mapping, although

assistance can be provided at the request of Emergency Management.

• Distributing Data to the Public - NC and VA both have websites for distributing geologic data, but there should be a better interface for serving data to the public.

VA DGMR Flexviewer: http://dmme.virginia.gov/webmaps/DGMR/

NCGS Landslide Hazard Maps: http://portal.ncdenr.org/web/lr/landslides-information

D

F

E

A

B

C

Type of rainfall event

Rainfall total (mm)

Time of most

intense rainfall

Landslide dates

mm/day/yr

Landslides reported State

Tropical Cyclone (unnamed) 564 24h 7/15-16/1916 Many, >45 North Carolina

Storm 584 24h 8/13/1916 1 North Carolina

Tropical Cyclone (unnamed) 254 6h 8/13-14/1940 2,120 North Carolina/

Tennessee

Storm 330 2d 8/28-31/1940 >200 North Carolina

Cloudburst 400 1d 6/17-18/1949 466 Virginia/ West Virginia

Tropical Cyclone Camille 710-800 8h 8/19-20/1969 3,793 Virginia

Thunderstorms 196 1h 5/26-28/1973 Many - 8 documented North Carolina

Extratropical Cyclone (unnamed) 300 2d 11/5-7/1977 13 North Carolina

Extratropical Cyclone (unnamed) 150 2d 11/5-7/1977 83 North Carolina

TC Juan 350 3d 11/3-5/1985 3,000 Virginia/ West Virginia

Storm 770 14h 6/27/1995 629 Virginia

Storm 635 1d 6/27/1995 72 Virginia

TC Opal 274 1h 10/3-5/1995 2 North Carolina

Storm 187 1d 5/5-7/2003 10 North Carolina

Tropical Cyclone Isabel 513 1d 9/18-19/2003 6 Virginia

Tropical Cyclone Gaston 320 8h 8/30/2004 Several hundred Virginia

Tropical Cyclone Frances 599 2d 9/6-8/2004

400+ North Carolina Tropical Cyclone

Ivan 432 2d 9/16-17/2004

Tropical Cyclone Cindy 110 2d 7/7/2005 1 North Carolina

Tropical Cyclone Ernesto 168 12h 8/31/2006 1 North Carolina

Storm 152 24h 1/7/2009 2 North Carolina

Storm 35 4h 2/5/2010 1 North Carolina

Thunderstorm 125 4h 7/14-15/2011 21 North Carolina

Storm 388 2d 1/14-17/2013 Many - 268 confirmed North Carolina

Storm 168 2d 5/4-6/2013 Many -50 confirmed North Carolina

Storm 250 2d 7/2-9/2013 Many - 9 confirmed North Carolina

Wayah debris flow, Macon County, NC

Debris Slide

Wedge Failure Slow-moving

weathered rock slide

Debris Flow

Private Residence, Macon County, NC

Private Residence, Haywood County, NC

Interstate-40 Haywood County, NC

A