Wintergreen Property Owner’s Association
88 Wintergreen Drive
Roseland, Virginia 22967
Attn: Jay Roberts/Executive Director

 

 

The Reeds Gap – Pond Hollow, 
Debris-Avalanche/Debris-Flow Collection Basin, 
Nelson County, Virginia

 

Some classic and very expensive induced landslide-failures in Virginia (e.g., along I-81 near Hollins, Roanoke Co.; along I-81 near Dixie Caverns, Montgomery Co.; and along I-64 near Afton Mountain, Albemarle,  Co.) should not have happened! Although geotechnical work may have been of high quality along the actual  right of ways, the geological mapping and broader assessment of the surrounding areas should have been one of  the required necessary and sufficient conditions needed to demonstrate that failure was likely. Thus, stretches  of these highways could have been relocated without disastrous results. 

On a recent visit to the Reeds Gap – Pond Hollow area in Nelson Co., it was apparent that some  geotechnical work (as indicated by cuttings at some shallow boreholes) had been done along a narrow proposed  pipeline route across the collection basin. This was near a debris-avalanche chute (Figure 1) that crossed VA  highway 664 near Reeds Gap. In 1969 I observed the 7-10m-high mud ring on trees that lined this chute. I also  observed that this debris avalanche stopped about 0.5 km down the mountain where the gradient flattened in  the catchment basin. I mapped the geology around Wintergreen (Bartholomew, 1971). I located and logged  some of the first water wells along the sheared granite/greenstone contact (Figure 1) drilled on top of the  mountain at Wintergreen (1971-1973). Later I published the Sherando and Greenfield quadrangles  (Bartholomew, 1977) where I mapped many of the debris avalanche chutes and later analyzed some of the  contributing factors that produced more than 1100 debris avalanches during Hurricane Camille (Gryta and  Bartholomew, 1987 and 1989). 

Being on the perimeter of the high rainfall area during Hurricane Camille, the Wintergreen area received  only a few debris-flows/debris-avalanches and only one occurred within the collection basin. Still that slide was  triggered along the contact (Figure 1) between Catoctin Greenstone and a weathered, thin phyllitic  metasediment with a gently dipping foliation. This contact is very similar to the contact between Catoctin  Greenstone and a thick, weathered phyllite that generated the Afton Mountain slide along I-64 near Royal  Orchards as well as similar contacts in the Wintergreen area.  

Thus, when I observe minimal geological and/or geotechnical work being done in an area where  repeated debris-flows/debris-avalanches are known to have occurred, I am concerned because I know that high rainfall events like Camille will happen again and again! Indeed, in a recent study (Soplata, Bartholomew, and  Wooten, 2016) along Hickory Nut Gorge near Chimney Rock, North Carolina, a Camille-type event killed seven  people and triggered about 300 debris avalanches in 1916. Major flooding occurred in 1994, 1996, 2008, and  2014. The 1996 rainfall event triggered a mudslide that pushed a house 150 feet down the slope of the gorge  (just 80 years after the 1916 event). Thus major rainfall events do not need a Camille-type storm to trigger  landslides. Even moderate rainfall and groundwater movement along faults and shear zones, bedding contacts,  foliation planes and joints can trigger landslides as witnessed by the tubing-park slope failure at Wintergreen  and the subsequent decision to move the water tank because of it. 

While Wintergreen was in its nascence, I recommended that the Pond Hollow access road not be used  as the principal access route to Wintergreen because of the high risk that the Reeds-Gap/Pond-Hollow collection  basin possesses from repeated debris-flows/debris-avalanches. Although the road was essential to gain access  to the mountain, Wintergreen did follow a policy that residential homes were not built along this roadway (Wintergreen Drive). By avoiding residential development in the basin, only people driving up or down the  mountain are at risk from major rainfall events. The Police Emergency and Command Center (Figure 1) was  placed at junction of VA Highway 664 and Wintergreen Drive to have a staging area for emergency deployment  to the mountain. The administration building for the Wintergreen Property Owners Association is located nearby  as well as several some maintenance buildings, but none of these are residences. 

My concern was magnified many times over when I recently visited and walked the route of the  proposed pipeline and learned of the intention to put a large, high pressure gas pipeline across the funnel of the tracks of many debris-flows/debris-avalanches. Considering the size of many very large boulders in past debris  flows and the sheer weight and size of these debris flows, a gas pipeline is not safe a safe structure to install on  the surface of the ground nor within surficial debris-flow deposits in this catchment area. The debris flow/debris-avalanche deposits in the collection basin are relatively shallow and a Camille-type rainfall event  centered on this collection basin could literally “pull the plug” and all of the deposits could be swept down the  funnel scouring the base of the granite floor with debris tracks!  

A tunnel bored within the granite bedrock beneath the surficial colluvial deposits, would provide better  protection to a pipeline (Figure 1). But considerable care must be exercised because SE-dipping lithologic  contacts, SE-dipping faults and shear zones, and a strong SE-dipping foliation all favor weathering and  groundwater movement down-slope toward and into the collection basin. The proposed pipeline actually  crosses a SE-dipping thrust fault that places highly sheared granitic gneiss over top of highly sheared  metasediments of the Swift Run Formation. Foliation in this ~30m-thick shear zone dips SE and is likely to be a  major conduit along which groundwater moves. Additionally, downhill from the thrust fault, two high-angle  faults likely cross this proposed pipeline. Along one of these two faults, two water wells were drilled along the  contact between sheared granite and the greenstone to depths of ~200 feet (Figure 1). The shear zone in the  granite was ~50 feet wide. These fault zones are also groundwater conduits. As was the case with the tubing park slope failure at Wintergreen, enhanced groundwater along a lithologic contact toward a shear zone  promoted weathering and contributed to slope failure. Problems with construction of the water tank at  Wintergreen were also linked to deep weathering of the Catoctin Greenstone and joint-sets within the  greenstone that promoted oxidation and deeper weathering near the fault zone.  

I have spent many years studying the sequence and relationships among different fracture sets to aid in  the understanding how groundwater flows through fracture systems (Bartholomew and Rich, 2012;  Bartholomew and Van Arsdale, 2012; Bartholomew et al., 1994, 1998, 2000, 2002, 2007, 2009; Evans and  Bartholomew, 2010) in crystalline rocks of the Appalachian Piedmont, Mesozoic Basins, and Coastal Plain  sediments, in part related to multi-year studies around the DOE Savannah River site (Bartholomew et al., 1995,  1996, 1997) and the “North Carolina low-level radioactive waste disposal facility project” (Bartholomew and  Fleischmann, 1993; Wooten et al., 2001). Any tunnel across the collection basin needs to be concerned that  groundwater flow within shear zones, along lithological contacts and faults, and through fracture sets is not  altered or redirected in ways that might enhance slope failures. 

Detailed geological mapping around the Reeds Gap-Pond Hollow collection basin should follow standard  practices in the collection and analysis of data, such as was done by Law Engineering, Inc. and Harding Lawson 

Associates in the multi-year assessments of the “North Carolina low-level radioactive waste disposal facility  project” for Chem-Nuclear Systems, Inc. in the 1990s. The procedures for mapping, trenching, coring,  groundwater studies, and geophysical investigations need to be standardized and rigorously applied so that  concerns for human safety are constantly maintained. For this and other projects, I have coordinated teams of  2-9 people for geological work. The NC project required more than 4000 feet of trenching with careful mapping  of soils, bedrock lithology, and structural features and public walk-throughs of the trenches where people can  ask whatever questions they feel are relevant. Such procedures insure public confidence in the work. Future  studies near Reeds Gap should include such things as Lidar, coring, OSL and 14C dating, and geophysical work  coupled with mapping of surficial deposits. Using such techniques can help avoid costly mistakes. 

I recommend that the pipeline be relocated and not be placed across this collection basin where the  geologic factors indicate greater concern for public safety.

Dr. Mervin J. Bartholomew 

North Carolina Licensed Geologist No. 583 (1987-2017)

 

  1. Bartholomew, M.J., 1971, Geology of the Humpback Mountain Area of the Blue Ridge in Nelson and Augusta Counties, Virginia: Ph.D.  dissertation, Virginia Polytechnic Institute & State University, Blacksburg, Virginia, 159p. 
  2. Bartholomew, M.J., 1977, Geology of the Greenfield and Sherando quadrangles, Virginia: Virginia Division of Mineral Resources, Publication  4, 43p. with 1:24,000-scale maps. 
  3. Bartholomew, M.J., Heath, R.D., Brodie, B., Evans, M.A., 1995, Year 1 Progress Report on the Structural Controls on the Groundwater Regime  of the Central Savannah River Area, South Carolina and Georgia: Earth Sciences & Resources Institute Report F128-95-01, 125 p.
  4. Bartholomew, M.J., Brodie, B.M., Lewis, S.E., Evans, M.A., Heath, R.D., Greenwell, R.A., Blanchard, J.S., Syms, F.H., 1996, Year 2 Progress  Report on the Structural Controls on the Groundwater Regime of the Central Savannah River Area, South Carolina and Georgia: Earth Sciences  & Resources Institute Report F128-96-01, 230 p. 
  5. Bartholomew, M.J., Lewis, S.E., Evans, M.A., Rich, F.J., Brodie, B.M., Heath, R.D., Greenwell, R.A., Pray, J.R., Whitaker, A.E., Blanchard,  J.S., Syms, F.H., 1997, Year 3 Final Report on the Structural Controls on the Groundwater Regime of the Central Savannah River Area, South  Carolina and Georgia: Earth Sciences & Resources Institute Report F128-97-01, 142 p.  
  6. Bartholomew, M.J., Brodie, B.M., Willoughby, R.H., Lewis, S.E., Syms, F.H., 2002, Mid-Tertiary paleoseismites: Syndepositional features and  section restoration used to indicate paleoseismicity, Atlantic Coastal Plain, South Carolina and Georgia, p. 63-74 in F.R. Ettensohn, N. Rast, C.E.  Brett, editors, Ancient Seismites: Geological Society of America, Special Paper 359, 190p. 
  7. Bartholomew, M.J., Evans, M.A., Rich, F.J., Brodie, B.M., Heath, R.D., 2009, Rifting and drifting in South Carolina: Fracture history in  Alleghanian granites and Coastal Plain strata. Carolina Geological Society 2009 Annual Field Trip: Georgia Southern University, Department of  Geology and Geography, Contribution Series no.2, 50p. 
  8. Bartholomew, M.J., Fleischmann, K.H., 1993, Structural characterization and analysis of the Wake/Chatham county potentially suitable site,  North Carolina: Earth Sciences & Resources Institute Report 93-04-432, 126 p. 
  9. Bartholomew, M.J., Fleischmann, K.H., Wilson, J.F., 1994, Structural features associated with the Jonesboro fault where it crosses U.S.  Highway 70, Wake County, North Carolina, p.69-74 in E.F. Stoddard, D.E. Blake, editors, Geology and Field Trip Guide, Western Flank of the  Raleigh Metamorphic Belt, North Carolina, Carolina Geological Society Field Trip Guidebook 1994: North Carolina Geological Survey, 110p. 
  10. Bartholomew, M.J., Rich, F.J., 2012, Pleistocene shorelines and coastal rivers: Potential sensitive indicators of Quaternary tectonism along the  Atlantic Coastal Plain of North America, p. 17-36 in Cox, R.T., Tuttle, M.P., Boyd, O.S., Locat, J., editors, Recent Advances in North American  Paleoseismology and Neotectonics East of the Rockies: Geological Society of America, Special Paper 275p. doi:10.1130/2013.2493(02). 
  11. Bartholomew, M.J., Rich, F.J., Lewis, S.E., Brodie, B.M., Heath, R.D., Slack, T.Z., Trupe, C.H., III, and Greenwell, R.A., 2007, Preliminary  interpretation of Mesozoic and Cenozoic fracture sets in Piedmont metamorphic rocks and in Coastal Plain strata near the Savannah River,  Georgia and South Carolina, p.7-37 in F.J. Rich, ed., Guide to Field Trips – 56th Annual Meeting, Southeastern Section Geological Society of  America: Georgia Southern University, Department of Geology and Geography, Contribution Series no.1, 198p.  
  12. Bartholomew, M.J., Rich, F. J., Whitaker, A. E., Lewis, S. E., Brodie, B. M., Hill, A. A., 2000, Preliminary interpretation of fracture sets in  Upper Pleistocene and Tertiary strata of the lower Coastal Plain in Georgia and South Carolina, p.19-27 in C. Abate, editor, A Compendium of  Field Trips of South Carolina Geology with Emphasis on the Charleston, South Carolina, Area; Conducted in Association with the Geological  Society of America – Southeastern Section Meeting, March 23-24, 2000 Charleston South Carolina: South Carolina Department of Natural  Resources, Geological Survey, Columbia, South Carolina, 65p. 
  13. Bartholomew, M.J., Van Arsdale, R., 2012, Structural controls on intraplate earthquakes, U.S.A., p. 165-189 in Cox, R.T., Tuttle, M.P., Boyd,  O.S., Locat, J., editors, Recent Advances in North American Paleoseismology and Neotectonics East of the Rockies: Geological Society of  America, Special Paper 493, 275p. doi:10.1130/2013.2493(08). 
  14. Bartholomew, M.J., Whitaker, A.E., Barker, C.A., 1998, Preliminary Mesozoic-Cenozoic brittle-deformation history of Eocambrian rocks (Ridgeway gold mine, SC), Carolina Terrane, p.19-27 in D.T. Secor, Jr., editor, 1998 Special Issue devoted to the 1998 Field Trip for the  Carolina Geological Society: South Carolina Geology, V.40, 83p.
  1. Evans, M.A., Bartholomew, M.J., 2010, Crustal fluid evolution during deformation, uplift, and exhumation of the southeastern Piedmont of the  southern Appalachians: Late Paleozoic through Mesozoic rifting, p. 553-577 in Tollo, R.P., Bartholomew, M.J., Hibbard, J.P., Karabinas, P.M.,  editors, 2010, From Rodinia to Pangea: The Lithotectonic Record of the Appalachian Region: Geological Society of America Memoir 206,  Boulder, Colorado, 956p. 
  2. Gryta, J.J., Bartholomew, M.J., 1989, Factors influencing the distribution of debris avalanches associated with the 1969 Hurricane Camile in  Nelson County, Virginia, p. 15-28 in A.P. Schultz, R.W. Jibson, editors, Landslide Processes of the Eastern United States and Puerto Rico:  Geological Society of America, Special Paper 236, 102p. 
  3. Gryta, J.J., Bartholomew, M.J., 1987, Frequency and susceptibility of debris avalanches induced by the 1969 Hurricane Camille in central  Virginia, p. 16-18 in A.P. Schultz, C.S. Southworth, editors, Appalachian Landslides: U.S. Geological Survey Circular 1008, 43p.
  4. Soplata, A., Bartholomew, M.J., Wooten, R.M., 2016, Historically destructive landslides of the Hickory Nut Gorge near Chimney Rock, North  Carolina: Geological Society of America, Abstracts with Programs, V.48, no.3, T7-poster 51. 
  5. Wooten, R.M., Bartholomew, M.J., Malin, P.E., 2001, Structural features exposed in Triassic sedimentary rocks near the proposed low-level  radioactive waste disposal site, southwestern Wake County, North Carolina, p.51-74 in Hoffman, W., editor, Guidebook for 2001 Geological  Society of America – Southeastern Section Meeting, April 5-6, 2001, North Carolina State University, Raleigh, North Carolina, 203p.