Relative-age relationships of debris flow deposits in the Southern Blue Ridge, North Carolina

Periods of increased landscape instability in the Southern Blue Ridge were assessed with relative ages of three sequences of debris flow deposits. The sequences consist of a series of lobate deposits that are expressed as step-like landforms on the floors of host valleys. Data were collected at three sites from soil pits on the toe and apex of debris flow deposits. Relative ages were obtained by qualitatively and statistically examining data on clast weathering, soil color, clay content, and iron species. Consistent results among the indicators of relative age demonstrate that they have utility in warm to temperate, humid environments. At each site, the topographically highest debris flow deposits are slightly older than those at lower elevations. One deposit at each of the three sites has a relative age that is very similar to that of one deposit at the other sites. This similarity in age indicates that an external factor, such as extreme precipitation, accounts for the formation of debris flows at approximately the same time in the geological past. One of the sites, however, also has deposits that are clearly younger than the deposits at the other sites, which indicates that intrinsic factors also affect the formation of debris flows in the region.