Karst features (cavities and sinkholes) in south-central Missouri generally occur where the<br>Gasconade Dolomite and Roubidoux formations are exposed to a near-surface environment.<br>Karstic cavities develop as carbonic acid (derived from atmospheric carbon dioxide and rainwater)<br>percolates through these carbonate rocks along permeability pathways (e.g., fractures, faults, etc.)<br>from ground level to the water table. The carbonic acid gradually dissolves the carbonate country<br>rock and forms cavities. If the roof rock above a developing void becomes structurally unstable,<br>the cavity will collapse. Collapse features expressed at the surface are referred to as sinkholes. In<br>south-central Missouri, subsurface cavities and sinkholes are common and constitute a significant<br>engineering hazard.<br>To elucidate the internal structure of sinkholes in south-central Missouri, ground penetrating<br>radar surveys were conducted at eight sites on the Fort Leonard Wood Military Reservation. The<br>sinkholes studied developed in the upper Gasconade Dolomite and lower Roubidoux Formation.<br>Data were acquired with both a 500 MHZ antenna and a 120 MHZ antenna. The 500 MHZ data<br>proved to be most useful in terms of imaging the internal structure of the sinkholes. Depths of<br>investigation varied between one and four meters.<br>On the 500 MHZ radargrams, the internal collapse structure of the sinkholes is imaged by laterally<br>discontinuous events which reflect both the dip and dislocated nature of the collapsed strata.<br>These data are important because they demonstrate that ground-penetrating radar can be used to<br>map sinkhole features and potentially identify void space to a depth of 4m.


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