Geoscience Reference
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Sand
Argillic
horizon
Limestone
Limestone
Paleo-
sinkhole
fIGURe 3.2 Ground-penetrating radar (GPR) data showing a paleo-sinkhole. The sand thickness is approx-
imately 1 m; underlying is an argillic horizon that drapes the limestone. Notice how the radar bands point
down. The limestone is shown by the hyperbolas.
low areas. These subsurface low areas are not obvious by viewing only the surface topography. A
conclusion one may arrive at after looking only at the surface diagram is that soil water and nutri-
ent movements would be toward the dolines. But by studying the subsurface topography of the clay
horizon and assuming it was acting as an aquatard, one can assess that solute movement would not
necessarily be in the direction of the dolines but may follow another pathway. This research would
not have been possible without the use of GPR.
Using GPR in karst environments has been one of the most successful applications of this
geophysical technology. Paleo-sinkholes can be identified by radar in optimum soil conditions
(Figure 3.2). Optimum conditions include relatively dry sands over a moist argillic horizon that
“drapes” the limestone. Breaks in the draping of the argillic horizon may indicate the existence of a
void or a cavity that has been filled in with collapsed material (Figure 3.3).
Gish et al. (2002) also did a study involving GPR to evaluate its use in identifying subsur-
face flow pathways in a 7.5 ha agricultural production field in Maryland. They commented that
understanding subsurface stratigraphy was critical to obtain accurate estimates of water fluxes in
Sand
Argillic
horizon
Limestone
fIGURe 3.3 An area showing the sands above the argillic horizon that drapes the limestone. The depth to
limestone varies greatly in short distances. This is located in an area in Florida known as “bare” karst.
 
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