Abstract

Ground-penetrating radar (GPR) was used to explore alluvial-fan complexes on the piedmont slopes of higher mountains in the Blue Ridge province of North Carolina. On young fans with relatively unweathered surfaces, 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 internal structures revealed by GPR profiles are few. The typical profile has a chaotic appearance and is composed of numerous discontinuous reflectors with varying dips and diffraction hyperbolas produced by boulders. On old abandoned fans that have been subjected to intense weathering, boulders in the deposits have decomposed and structures subparallel to the surface are more likely to be seen. Continuous reflectors that may indicate contacts between depositional units, buried soils, or groundwater tables, however, are rare in both kinds of fans. Generally radar velocity and penetration are greatest on young fans, less on old fans, and least on saprolite.

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