USE OF ELECTRICAL RESISTIVITY TO DISTINGUISH EARTH MATERIALS IN THE APPALACHIANS WITH SPECIAL APPLICATION TO DEBRIS FLOW DEPOSITS IN GRAVES MILL, VIRGINIA

Mapping and characterizing debris flows is important to obtain information useful in identifying locations and conditions prone to possible future hazardous debris flow events and identifying and characterizing actual debris flow deposit material. Two-dimensional electrical resistivity profiling was completed at 16 sites in Virginia and Northeast Tennessee to determine if this geophysical technique was useful in identifying debris flow deposits. Electrical characteristics of six different geological substrata were used to help distinguish debris flow deposits. The resistivity of debris flow materials was found to be dependent upon the clay content in the matrix and the void ratio; “young” debris flows with low clay contents and high void ratios have average resistivities exceeding 1,250 ohm-m. In the period between flow events residual soils with higher clay content developed. Therefore in areas of accumulation, debris flows are commonly seen as layers of high resistivity above soils of low resistivity. The Wenner array produced a more accurate model of the subsurface than the dipole-dipole array. This was due to the extremely high lateral and vertical variability of subsurface due to layering and large boulders.