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Groundpenetrating radar (GPR) data were collected over a 10year period on sites composed of loess overalluvium over Tertiary sands. During wet periods, radargrams exhibited ephemeral columnar patterns occurring in andaround the alluvium/Tertiary sand interface. Following prolonged dry periods, radargrams did not exhibit the columnarpatterns. Extracted soil cores contained vertical preferential flow paths and vertical macro pores. A trench excavationrevealed increased preferential flow paths in those areas that exhibited columnar patterns. Conductivity shifts and sharperdielectric contrasts of localized moisture ponded or drained at this interface may cause reverberation patterns beneath.
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Freeland et al. (2002) studied this question.
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