GROUND-PENETRATING RADAR EXPLORATION OF ALLUVIAL FANS IN THE SOUTHERNBLUE-RIDGE PROVINCE, NORTH-CAROLINA

Ground-penetrating radar (GPR) was used to explore alluvial-fan comple xes on the piedmont slopes of higher mountains in the Blue Ridge provi nce of North Carolina, On young fans with relatively unweathered surfa ces, GPR penetration reached 16 m with 100 MHz antennae and 25 m with 25 MHz antennae. Penetration appears to be deepest near fan apexes. As the fans are composed mainly of bouldery debris flow deposits, the in ternal structures revealed by GPR profiles are few,The typical profile has a chaotic appearance and is composed of numerous discontinuous re flectors with varying dips and diffraction hyperbolas produced by boul ders, On old abandoned fans that have been subjected to intense weathe ring, boulders in the deposits have decomposed and structures subparal lel to the surface are more likely to be seen. Continuous reflectors t hat may indicate contacts between depositional units, buried soils, or groundwater tables, however, are rare in both kinds of fans, Generall y radar velocity and penetration are greatest on young fans, less on o ld fans, and least on saprolite.