PRELIMINARY STUDY OF MASS WASTING OCCURRENCES ALONG THE MIDDLE SALUDA RIVER, JONES GAP STATE PARK AREA, GREENVILLE COUNTY, SOUTH CAROLINA

Mass wasting events occur regularly in the southern Appalachians, and efforts have been made to identify these potential hazard areas. Jones Gap State Park (JGSP) is in NW Greenville County, South Carolina. We re-examined two recent debris flows, both triggered by heavy rainfall, (1976 and 2006) in JGSP in order to help identify and characterize older mass wasting occurrences in the steep-sided Middle Saluda River valley (local relief of 1600 ft). The 2006 flow is different from the 1976 event in that its channel is longer, narrower, steeper, and has steeper walls. The 2006 event also has less accumulation of soil and sediment in the apron. The presence of favorably oriented joints and exfoliation surfaces at both localities increased the potential for mass wasting. At the top of the 2006 slide, the exfoliation surface is the slide surface and is oriented N83E 45SE.

Tree cores were measured from the 1976 debris flow to determine a lag time between event and vegetation repopulation. Cores observed from the older trees in the channel were as old as 26 years, leaving a 7 year lag time. Small, deciduous trees in the 2006 channel provide a 3.5-year lag time, which is close to the lag time provided by tree coring.

Pre-1976 mass wasting events were identified by ground observations and contour features visible on 1:24,000 scale topographic maps. Overlapping aprons of mass-wasted debris line the lower parts of the north- and south-facing slopes of the Middle Saluda River valley. Upper slopes are steeper and are typified by balds of exposed Table Rock gneiss. Data from the 1976 event indicate slopes above the balds are potential source areas for future mass wasting.

Using observations from recent, well characterized events, we defined a ranking system, which ranks how likely a site may be a historical mass wasting event based on factors such as boulder accumulation, debris accumulation, rock scarring, channel shape, and the occurrence of springs/streams and joints.