Some Aspects of Linear Karst Depression Development in South Central Kentucky

This investigation attempts to analyze the spatial patterns of karst depression elongation and orientation relative to structural trends in a part of south central Kentucky. Depression elongation is defined by the ratio of the long axis of the depression to its short axis. Depression orientation is measured by the azimuth of the long axis in relation to the azimuth of an associated line of structural fracture. From these data the percentage of structurally aligned depressions was determined. The percentage of structurally aligned depressions was found to be highest where the following conditions prevailed: 1) in areas where limestones were characterized by low insoluble residue contents; 2) in areas where hydraulic gradients were high, as indicated by the existence of high karst relief ratios; 3) in areas where a high proportion of the surface runoff was concentrated in the subterranean drainage systems; and 4) in areas, which were located near the mouth of the subterranean drainage system. (Location in the subterranean drainage system was estimated by the mean distance to the drainage system mouth.) The percentage of structurally aligned depressions tended to decrease as the insoluble residue contents in the limestones increased, the karst relief ratios decreased, the percent area drained by subterranean streams decreased, and the mean distance from the drainage system mouth increased. Depression elongation ratios were highest in areas characterized by the following conditions: 1) low limestone insoluble residue contents; 2) high karst relief ratios, indicating high hydraulic gradients; 3) the presence of dense limestones; 4) proximity to the drainage system mouth; and 5) a high proportion of structurally aligned depressions (in this region this tended to be the most important factor influencing depression elongation). Depression elongation ratios decreased where any combination of the five previously described conditions did not occur in the optimum state. Regression analysis accounted for fifty-seven percent of the spatial variation of the distribution of structurally aligned depressions and eighty-eight percent of the variation of elongation ratios.