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2008 annual meeting – Spruce Pine Mining District: Little Switzerland, North Carolina
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STOP No. 2 -- Crabtree Meadows Rock Slide – June 15, 1999 rock
slide in interlayered metagraywacke and schist of the Alligator
Back Formation near Crabtree Meadows.
By: Rick Wooten, Rebecca Latham, and Bart Cattanach.
Leaders: Rick Wooten, Bart Cattanach
Location: GPS latitude 35.81442 N, longitude 82.13971 W; approximately 0.2 mi (0.3 km) northeast of
Crabtree Meadows.
PURPOSE: To observe lithologic and structural features in bedrock related to rock slope instability in a
road cut through interlayered metasedimentary rocks of the Alligator Back formation.
WARNING: Be extremely careful around the rock cut. Rock slides and rock falls may occur
suddenly without warning.
Background. The June 15, 1999 rock slide at this location blocked the Blue Ridge
Parkway (the Parkway) for several days (Fig. 1). Rockslide debris included one intact
block estimated to have weighed about 800-1,000 tons (725-907 metric tons) (A.Glover,
personal communication). Periodic slope movements, primarily rock slides and
embankment failures that make the Parkway impassable are costly to repair, and
adversely affect communities that depend on income from tourism along the Parkway.
Figure 2 shows the stop location on the Parkway, and other mapped slope instability
features in the vicinity.
Identification and analysis of rock slope stability was a major part of the geologic and
geohazards studies recently completed by the North Carolina Geological Survey (NCGS)
along the North Carolina segment of the Parkway. That inventory identified 172 pastactive
or active slope movements including rock slides, rock falls, weathered-rock slides,
embankment failures, and debris flows, as well as 138 locations (57 of which are also
active or past active and 81 that have no known history of failure) that have the potential
for future rock slides and rock falls. Rock slope failures occur for the most part along
cut slopes and are generally confined to the Parkway corridor. Some of the inventoried
embankment failures are subsiding roadway segments marked by arcuate cracks in the
pavement. Other embankment failures, however, mobilized into debris flows triggered
by rainfall from the remnants of Hurricane Frances in September 2004. A number of
these roadway failures traveled down slope significant distances causing damage on land
administered by the U.S. Forest Service (Collins, 2007).
Description. Figure 3 shows the current slope configuration along with structural and
lithologic features that relate to the rock slope stability. Rock slope data were provided to
the National Park Service in this format with the image and explanatory data hot linked to
ArcGIS data layers showing point locations of observed instability features. Other
examples of these rock slope stability assessments along the Parkway are given in
Latham and Wooten (2005). Here, an undulatory dominant foliation parallels
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