Rockslide of February 17-18, 2001
(courtesy of Richard M. Wooten & Timothy W. Clark, NCGS)

3. Weather conditions

Daily high and low temperature record for Eno River State Park (ER) and Raleigh-Durham Airport (RDU) showing freeze-thaw cycles during January and February 2001. Note: Constant high and low temperatures over 2-4 day periods for Eno River State Park reflect gaps in recorded data.

 Repetitive freeze-thaw cycles over decades can lead to frost-wedging along fractures and other discontinuities, contributing to the forces driving the rock mass down slope. A further destabilizing affect results from infiltrating rainfall that causes the build-up of water pressure along discontinuities. As can be seen in the charts, numerous freeze thaw cycles during January and February 2001 preceded a 0.98-inch rainfall on February 17, 2001. These recent weather patterns that reflect similar patterns over the decades may have been the short term triggering mechanism for the February 17-18, 2001 rockslide.

Daily precipitation data recorded for Eno River State Park (ER) and Raleigh-Durham Airport (RDU) during January and February 2001. Trace precipitation plotted at 0.01 inches. Note: Precipitation totals recorded over intervals greater than one day for Eno River State Park are plotted on the last day of the reported interval.

The slopes below the rockslide scarp remain hazardous. Loose rock, oversteepened slopes, and rock overhangs in the scarp area are unstable.  Park staff members reported audible rock fall in the quarry area about 9:00 p.m. on April 13, 2001. Both Park and NCGS staff observed dilation of fractures (J2) in the scarp area indicating that rock fall along with sliding and toppling of large blocks of rock will continue to occur in the months, and possibly years, to come.

Copyright © Jean-Michel Margot
Date: 2001/09/23